1. Introduction

Neuroimaging provides a tool for examining the biological development of the human brain in vivo. A primary aim of the ABCD study is to track human brain development from childhood through adolescence to determine biological and environmental factors that impact or alter developmental trajectories. This landmark study is recruiting and following approximately 10,000 9–10 year olds across the United States. Longitudinal measures of brain structure and function are a central focus of the study. The ABCD Imaging Acquisition Workgroup https://abcdstudy.org/scientists-workgroups.html selected, optimized and harmonized measures and procedures across all 21 ABCD sites. This article provides the basis for, and overview of, the ABCD imaging procedures and preliminary quality assessments that indicate the developmental appropriateness of the protocol for 9 and 10 year olds.

Numerous Big Data studies have emerged around the world (Rosenberg et al., under review 2018) that assess human brain function and structure with magnetic resonance imaging (MRI) of the developing mind and brain. The ABCD study capitalizes on the advancing technologies in structural and functional MRI of these studies, especially from the Human Connectome Project (HCP; https://www.humanconnectome.org ) and the Pediatric Imaging, Neurocognition, and Genetics (PING) Study (http://pingstudy.ucsd.edu , Jernigan et al., 2016) and components of the IMAGEN study (www.imagen-europe.com; Schumann et al., 2010) that combines brain imaging and genetics to examine adolescent development and human behavior.

Building upon the efforts of these Big Data studies has led to the establishment of an optimized MRI acquisition protocol to measure brain structure and function that is harmonized to be compatible across three 3 tesla (T) scanner platforms: Siemens Prisma, General Electric 750 and Phillips at 21 sites. The protocol includes 3D T1- and 3D T2 weighted images, and diffusion weighted images for measures of brain structure; and resting state and task-based functional MRI for measures of brain function.

ABCD task-based functional assessment of the brain consists of three tasks: the Monetary Incentive Delay (MID) task (Knutson et al., 2000), the Stop Signal task (SST, Logan, 1994b) and an emotional version of the n-back task (EN-back, Cohen et al., 2016b; Barch et al., 2013). Together these tasks measure 6 of the original National Institutes of Health's Collaborative Research on Addiction at NIH (CRAN) Request for Applications (RFA)-mandated domains of function: reward processing, motivation, impulsivity, impulse control, working memory and emotion regulation. Each of the 6 behavioral domains measured by the ABCD fMRI tasks are highlighted in Table 1 indicating behavioral domain, task, processes and neural correlates. Table 1. Domains of function measured by the ABCD fMRI tasks.

2. ABCD materials and methods

An important motivating factor for the study is to identify developmental trajectories and neural signatures for adolescent mental health. To ensure that the study has the statistical power to characterize these different developmental trajectories, an aim of the study is for approximately 50% of the sample to consist of children who show early signs of externalizing and internalizing symptoms. The sample and overall design of the ABCD study are described by Garavan et al., Loeber et al. and Volkow et al. this issue. Also, see Clark et al. (this issue) for details on ethical considerations of the study. The imaging protocol, procedures, and tasks are described in detail below with emphasis on harmonization of procedures across the 21 ABCD sites.

2.1. Equipment and software

2.1.1. Scanner and head coil

The ABCD imaging protocol is harmonized for three 3T scanner platforms (Siemens Prisma, General Electric (GE) 750 and Philips) and use of multi-channel coils capable of multiband echo planar imaging (EPI) acquisitions, using a standard adult-size coil. The decision to use a standard head coil for each scanner platform across ages rather than using nonstandard customized coils was threefold. First, 9 and 10 year olds have brains that are typically between 90 and 95% of adult brain size. There is empirical evidence for the feasibility of using a common stereotactic space for this age as that used for adults (Burgund et al., 2002; Kang et al., 2003). Second, the use of custom coils for each age would introduce significant challenges to the analysis with the coil being confounded with age. Third, custom coils require the manufacturer to produce and provide customization of coils and connectors that was not feasible to obtain across all sites during the first year of optimization and harmonization of the scan protocol. It has been important throughout the design of the ABCD study to coordinate with the vendors to ensure stability of the hardware from the start of the study in September 2016 and over the course of this 10-year study.

2.1.2. Stimulus presentation and response collection

The task-based fMRI scans require special stimulus presentation and response collection equipment and software. All ABCD fMRI tasks are currently programmed in E-Prime Professional 2.0 versions 2.0.10.356 or later and work reliably for PC Windows 8.1 or earlier. The tasks and stimuli are available for download at: http://fablab.yale.edu/page/assays-tools . The response collection device is harmonized for precision in response latency across all tasks and all sites with a Current Designs 2- button box. The tasks are programed to accept input from the dominant hand (left or right). Visual display and auditory delivery equipment are not harmonized given the variability in scanner and control room set-up across sites and no mandate for precise visual or auditory resolution for the fMRI tasks was imposed. Sites use rear projection or goggles for visual display and a variety of head phone/ear bud devices. Tasks are programmed to accommodate these various set-ups across sites.

3. ABCD scan protocol

The ABCD neuroimaging protocol is depicted in Fig. 1. The final ABCD protocol was based in part on a multi-site (12 ABCD sites) pilot study of a convenience sample of 67 children and teens from varied household incomes and racial and ethnic backgrounds and included individuals at risk for substance abuse and mental health problems. Over 30 of these children provided imaging pilot data. These data showed no more fatigue, as measured by poorer fMRI task performance and self-report, when completing the scan protocol in one session versus two, or when administering the fMRI tasks at the beginning of the scan session versus at the end. Thus, scanning occurs in either 1 or 2 sessions. Varying the number of scan sessions provides added flexibility for sites that have constraints in scanner access and aids in accommodating constraints that ABCD families may have in their schedules, etc. In addition to the pilot data, further evidence of the feasibility of the ABCD imaging protocol for 9–10 year olds is indicated by the high completion of scans for the first approximately 1000 subjects. These data show that 99% of the enrolled subjects completed the 3D T1-weighted scan. The remaining scans varied in completion from 88 to 98% (rs-fMRI = 98%, diffusion = 97%, 3D T2 = 96%, MID = 91%. SST = 89% and the EN-back = 88%). Thus, completion of all scan types across sites is at nearly 90%.

Fig. 1. ABCD Neuroimaging Protocol

3.1. Ordering of scans

The scan session consists of a fixed order of scan types that begin with a localizer, acquisition of 3D T1-weighted images, 2 runs of resting state fMRI, diffusion weighted images, 3D T2-weighted images, 1–2 more runs of resting state fMRI (see motion detection below for when to acquire 1 versus 2 additional runs) and the task-based fMRI. Although the order of scans across subjects is fixed as shown in Fig. 1, the order and version of the 3 fMRI tasks (MID, SST and EN-back) are randomized across subjects. The decision to randomize the order of fMRI tasks across subjects was based in part on these scans being the most cognitively demanding on the child. Whereas, the structural and resting state scans simply require the child to relax and watch a movie or look in the general direction of a fixation crosshair, the fMRI tasks require anticipation and outcome of rewards and losses, impulse control, emotion regulation, memory and action on the part of the child (see Table 1. Domains of function measured by the ABCD fMRI tasks). Also, negative affective processes can diminish cognitive performance (Cohen et al., 2016a) and performing a demanding cognitive task has been associated with diminished performance on subsequent tasks (Baumeister et al., 1998). We therefore randomized the order of tasks across subjects to help control for these effects.

Likewise, we randomized the order of trials within tasks to help control for the effects of different processing demands of one trial on a subsequent trial. Based on simulations, 12 pseudorandom trial sequences optimized to minimize variance in activation parameter estimates were selected for tasks with event related designs (MID and SST). This allows investigators to assess generalizability over task variants (trial sequences) and control for sequence if necessary. The EN-back was programmed as a block design given time constraints, number and level of factors (4 stimulus types, 2 memory loads) and the need for instructed task switching between memory load conditions.

Finally, the random assignment of a given order and version of tasks to a subject at baseline is held constant across longitudinal scans to minimize within-subject variability and enhance the ability to test key ABCD specific aims that focus on individual differences in developmental trajectories. In addition, participants within a family (e.g., twin pairs/siblings) receive the same order and version of the fMRI tasks to minimize within-family variability for testing heritability and genetic effects. Details of the imaging protocol are described in detail below for each component: pre-scan, scan and post-scan.

3.2. Pre-scan assessments and training

3.2.1. MR screening

Participants complete an MR screening questionnaire for any contraindication for an MRI (e.g., braces, pacemakers, and other metal in the body including piercings, medical screw, pins, etc.). This MR screening occurs three times: during initial recruitment, at scheduling, and just prior to the scan.

3.2.2. Simulation and motion compliance training

Before the scan, participants are desensitized to the scanner environment with a simulator. Simulation occurs in dedicated mock scanners with prerecorded scanner sounds and/or collapsible play tunnels the diameter of the scanner bore (55–60 mm). Because head motion is a significant problem for pediatric imaging, behavioral shaping techniques are used for motion compliance training (Epstein et al., 2007). Commercial simulators, or Wii devices affixed to the child’s head (see Supplemental Text) monitor head motion and provide feedback to the child. After simulation and motion compliance, the participants practice the three fMRI tasks to be sure they understand the instructions and are familiarized with the response collection device.

3.2.3. Arousal questionnaire

Immediately prior to scanning, the participant is given a restroom break and then administered a questionnaire on his/her current state of arousal (Supplemental Table 1). This questionnaire is administered again at the end of the scan (see Post Scan Assessments). Earplugs are inserted, and the child is placed on the scanner bed. Physiologic noise is measured with a respiratory belt placed around the child’s stomach to measure breathing rate and a pulse oximeter placed on the child’s non-dominate pointer finger to measure heart rate. To minimize motion, the head is stabilized with foam padding around head phones/earbuds. The technologist localizes the head position, ensures that the child can fully view the screen, and has the child test the response box buttons. As the scanner table moves to the center of the scanner bore, a child appropriate movie is played and the staff makes sure the child can see and hear it.

3.3. Scan session

A child friendly movie is turned on as the child enters the scanner and remains on during acquisition of the localizer and 3D T1 scans and is also played during the 3D T2 and diffusion weighted imaging acquisitions. The functional scans include twenty minutes of resting-state data acquired with eyes open and passive viewing of a cross hair. One set of two 5 min runs is acquired immediately after the 3D T1 and another set is acquired after the 3D T2 scans. The task-based fMRI images are completed after the final set of resting state scans, counterbalancing the order of tasks across subjects.

3.3.1. Scanning parameters

The imaging parameters for the 3 three 3T scanner platforms are summarized in Table 2. This protocol is shared, although some platforms require agreements for the research sequences, so that every ABCD site can download the protocol and install it with no need for manual entry of parameters, which reduces the likelihood of human error. Images are acquired in the axial plane rather than the oblique orientation since oblique EPI prescriptions are not supported/recommended by GE and Phillips due to ghosting and the potential for peripheral nerve stimulation as the scan plane gets closer to the coronal plane or the phase encoding direction gets closer to the left-right direction. Scan sequences continue to be optimized and made available as the scanner instrumentation is upgraded and improves (e.g., Siemens Prisma upgrade from version VE11B to VE11C). As the technology and sequences are optimized, human phantoms are being collected on all scanners and all software versions within and between sites to control for these changes. Table 2. ABCD harmonized imaging scanning parameters for Siemens Prisma, Phillips and GE 750 3T scanners.

Each scan type measures unique aspects of brain structure and function. The 3D T1-weighted magnetization-prepared rapid acquisition gradient echo scan is obtained for cortical and subcortical segmentation of the brain. The 3D T2-weighted fast spin echo with variable flip angle scan is acquired for detection and quantification of white matter lesions and cerebral spinal fluid (CSF). The high angular resolution diffusion imaging (HARDI) scan, with multiple b-values, and fast integrated B₀ distortion correction (Reversed polarity gradient (RPG) method, Holland et al., 2009; Treiber et al., 2016), is acquired for segmentation of white matter tracts and measurement of diffusion. Finally, high spatial and temporal resolution simultaneous multi-slice (SMS)/multiband EPI resting-state and task-based fMRI scans, with fast integrated distortion correction, are acquired to examine functional activity and connectivity.

3.3.2. Motion detection and correction

Real-time motion detection and correction for the structural scans are implemented by the ABCD DAIC hardware and software. Specifically, anatomical 3D T1- and 3D T-2 weighted images are collected using prospective motion correction (PROMO) on the GE (White et al., 2010), Volumetric Navigators (vNav) for prospective motion correction and selective reacquisition on the Siemens and when available on the Philips platform (Tisdall et al., 2012).

A real-time head motion monitoring system called FIRMM (fMRI Integrated Real-time Motion Monitor, (www.firmm.us , Dosenbach et al., 2017) collaboratively developed at Washington University, St. Louis and Oregon Health Sciences University is implemented for motion detection in resting state fMRI scans at the Siemens sites. FIRMM allows scanner operators to adjust the scanning paradigm based on a participant’s degree of head motion (i.e., the worse the motion, the less usable data and greater the need for more data to be acquired).

Head motion is a significant concern for pediatric imaging and has received significant attention in the domain of rs-fMRI (Fair et al., 2012; Power et al., 2012, Power et al., 2013; Satterthwaite et al., 2012; Yan et al., 2013a, Yan et al., 2013b; Van Dijk et al., 2012). Preliminary motion data are presented in Fig. 2. Motion-detection, −correction and −prevention training are used to help minimize motion. Preliminary analysis of frame-to-frame displacement of over 2500 participants during resting-state and task-based fMRI data. are provided in Fig. 2. Mean motion is 0.22 mm during rest (SD = 0.20 mm) and less than 0.29 mm in all tasks (n-back M = 0.28, SD = 0.27; SST M = 0.26, SD = 0.25; MID M = 0.25, SD = 0.23). Before mean motion was computed, data were temporally filtered to remove aliased respiratory signals. Future data releases will include six-parameter motion time courses and optimized measures of overall head motion.

Fig. 2. Preliminary distribution of head motion during resting-state and task-based fMRI scans. Box plots show the distribution of average frame-to-frame displacement during resting-state and emotion (E) N-back, stop-signal task (SST), and monetary incentive delay (MID) task runs from participants with all four scan types (n = 2536). The lower and upper box hinges correspond to the 25th and 75th percentiles; horizontal lines show median values; and dots represent individual participants.

Together, the data are relatively encouraging given the young age of the participants (9–10 years), length of the scan protocol (100–120 min), and that approximately 42% of the sample consists of children who show early signs of externalizing and internalizing symptoms and considered at risk for substance abuse and other mental health problems. See Garavan et al., Loeber et al. and Volkow et al. this issue on the study design, recruitment and screener for children at risk for substance abuse and other disorders.

3.3.3. The fMRI tasks

Specific details for each of the fMRI tasks and preliminary quality assessment and results are provided below. These tasks measure processes relevant to addiction and adolescent development and have shown well-characterized and reliable patterns of brain activity in prior imaging studies (refer to Table 1 for a summary). The three tasks were selected based on the existing literature indicating that they met 6 important criteria: 1) implication in addiction (validity); 2) feasibility in developmental studies (developmentally-appropriate); 3) well-characterized neural activations (specificity); 4) reliable activation over time within subjects (reliability); 5) consistent patterns of activity across subjects (sensitivity); and 6) leveraging of other complementary developmental imaging initiatives that use similar measures (generalizability). The relevant literature supporting these claims are provided in the description of each task.

3.3.3.1. Monetary Incentive Delay Task (MID)

The MID task used in the ABCD study (Knutson et al., 2000; Yau et al. 2012) measures the original CRAN ABCD RFA domains of reward processing, including anticipation and receipt of reward and losses, and trial-by-trial motivation in speeded responses to win or avoid loss (Fig. 2). The MID task is a robust activator of the ventral striatum, demonstrating validity as probe of reward responding (Knutson et al., 2000). This task is sensitive to developmental (Bjork et al., 2004, Bjork et al., 2010; Heitzeg et al., 2014) and addiction-related effects (Andrews et al., 2011; Balodis and Potenza, 2015; Beck et al., 2009; Villafuerte et al., 2012; Wrase et al., 2007; Yau et al., 2012) and has good within-subject reliability over time (Villafuerte et al., 2014).

Each trial of the MID task begins with an incentive cue (2000 ms) of five possible trial types (Win $.20, Win $5, Lose $.20, Lose $5, $0-no money at stake) and is followed by a jittered anticipation event (1500–4000 ms). Next, a variable target (150–500 ms) appears during which the participant responds to either win money or avoid losing money. This target event is followed by a feedback message informing the participant of the outcome of the trial. The duration of the feedback is calculated as 2000 ms minus the target duration. The task consists of twelve optimized trial orders of the task (2 runs each). Each run consists of 50 contiguous trials (10 per trial type) presented in pseudorandom order and lasts 5:42.

Task performance is individualized with the initial response target duration based on the participant’s performance during a practice session prior to scanning. Performance is calculated as the average reaction time (RT) on correct trials plus two standard deviations. To reach a 60% accuracy rate, the task difficulty is adjusted over the course of the task after every third incentivized trial based on the overall accuracy rate of the previous six trials. If the participant’s accuracy falls below the target accuracy level, the duration of the target is lengthened. If the participant’s accuracy is above the target accuracy level, the target duration is shortened. Participants gain an average of $21 and all subjects are given at least $1 regardless of performance to maintain motivation during the scan protocol. Hits, RT and monetary payout are calculated (Fig. 3).

Fig. 3. Monetary incentive delay task.(Adapted from Knutson et al., 2001)

For the MID task, the following primary conditions are modeled: reward vs. no money anticipation, loss vs no money anticipation, reward positive feedback vs reward negative feedback, loss positive feedback vs loss negative feedback. Each participant receives 40 reward and loss anticipation trials and 20 no money anticipation trials. For feedback, the adaptive algorithm results in 24 positive feedback trials (for both reward and loss) and 16 negative feedback trials (for both reward and loss) on average.

Preliminary behavioral data from the MID task (n = 965) suggest that the experimental manipulation to maintain hit rates at close to 60% is working. Average hit rates are between 50 and 60% and these rates are maintained across experimental runs (see Fig. 4a). As reported in the literature (Bjork et al., 2010), the average hit rate is slightly higher for reward (59%) and loss trials (54%) than for neutral trials (49%). Reaction times appear relatively stable across runs and conditions. Finally, as anticipated, participants earned on average $21.43 with consistent payoff amounts across experimental runs of $10.56 and $10.87. With age, it will be important to examine variation in response latencies on win and loss trials relative to neutral ones to assess development effects.

Fig. 4. Preliminary results for the MID task. A. Hit rate and reaction time are presented as a function of loss, reward and neutral trials for the first and second half of the data (Run 1 and Run 2). B. Cortical (top) and subcortical (bottom) maps for the contrast of reward success vs fail (signed Cohen’s d) show reliable activation of expected brain circuitry in medial prefrontal cortex (top) and the ventral striatum (bottom).

Preliminary examination of the MID imaging data look promising. Fig. 4b depicts signed effect sizes (Cohen’s d) for the contrast of rewarded trials versus failed trials (n = 856). These images show the expected pattern of increased activity in the ventral striatal striatum and medial prefrontal cortex to reward (Fig. 4b). It will be important to examine how these patterns change and differ for children at risk for substance abuse across development.

3.3.3.2. The stop signal task (SST)

The SST (Logan, 1994a) engages core brain networks and RFA domains of impulsivity and impulse control (Whelan et al., 2012; Hart et al., 2012); activates key brain regions across subjects with impulsivity problems (Hart et al., 2012); shows adolescent-specific and addiction effects (Whelan et al., 2012; Smith et al., 2014); and leverages data being collected as part of IMAGEN (Whelan et al., 2012; Schumann et al., 2010).

The SST requires participants to withhold or interrupt a motor response to a “Go” stimulus when it is followed unpredictably by a signal to stop (Fig. 5). Each of 2 runs contains 180 trials. Each trial begins with the presentation of a leftward or rightward pointing arrow in black on a mid-grey background. Participants are instructed to indicate the direction of the arrow, responding “as quickly and accurately as possible” via a two-button response panel. Participants respond with their dominant hand and stimulus/response mapping is congruent with handedness. Thirty of the trials (16.67%) are “Stop” trials on which the leftward or rightward facing arrow is followed unpredictably by the “Stop Signal”, that is an up-right arrow presented for 300 ms. The greater frequency of “Go” trials establishes a strong prepotent “Go” response

Fig. 5. Stop signal task. Examples of Go and Stop trials with timing are provided. ITI = Inter-trial interval; RT = Reaction time; SSD = Stop signal delay; SS = Stop signal.(Adapted from Helfinstein and Poldrack, 2012)

To ensure that there are approximately 50% successful and 50% unsuccessful inhibition trials for Stop trials, a tracking algorithm varies the interval between the onset of the leftward or rightward facing arrow and the onset of the Stop Signal (Stop Signal Delay: SSD). The initial SSD is 50 ms. Following an unsuccessful inhibition, the task is made easier by reducing the SSD by 50 ms on the next Stop trial. Following a successful inhibition, the task is made more difficult by increasing the SSD by 50 ms on the next Stop trial.

Each trial lasts 1000 ms: Go trials comprise a response terminated arrow (50% rightward facing) followed by a fixation cross of variable length for a total trial duration of 1000 ms; Stop trials comprise the arrow (50% rightward facing) presented for the duration of the SSD as determined by the algorithm followed by a 300 ms Stop Signal, and then by a fixation cross for a total duration of 1000 ms. Stimulus Onset Asynchrony (SOA) ranges from 1700 ms to 3000 ms with a mean SOA of 1904 ms. The number of Go trials separating Stop trials ranges from 1 to 20 with a mean of 4.91 trials. Each run terminates with a variable length fixation cross to bring the experimental length of each run to 349 s. The length of the final fixation cross ranges from 1038 ms to 8817 ms, with a mean of 4297.625 ms. Twelve optimized trial orders were generated, constraining the first trial of each run to be a Go trial and separating Stop trials by at least one Go trial. Stop signal reaction time (SSRT), RTs on Go trials, and accuracy are key dependent measures. In total there are 360 trials across 2 runs. Each run consists of 150 Go trials and 30 Stop trials, with the anticipation of 15 successful inhibitions and 15 failed inhibitions for a total of 300 Go trials and approximately 30 successful Stop trials and 30 failed Stop trials.

Preliminary behavioral results on the SST task (n = 965) show that the algorithm to ensure an approximately equal number of successful and unsuccessful inhibition (stop) trials is working with just over 50% stop error trials (See Fig. 6a). Accuracy on the go trials is over 80% with fewer than 20% of trials coded as incorrect due to a late response, error (i.e., pressed incorrect button) or no response. This performance is maintained across the experimental runs of the task. The SSRT appears to decrease over runs indicating improved inhibitory ability over time.

Fig. 6. Preliminary Results for the SST. A. Accuracy and reaction times are presented as function go and stop trials. B. Cortical patterns of brain activity (signed Cohen’s d) for the contrast of correct stop vs correct go trials (top) and subcortical activity in the putamen for correct stop trials vs error stop trials. SSRT: stop signal reaction time; SSD: stop signal delay.

Preliminary examination of the SST imaging data look promising too. Fig. 6b depicts the signed effect sizes (Cohen’s d) for the contrast of correct stop trials vs correct go trials (n = 750). There is robust activation of the lateral prefrontal cortex, anterior cingulate cortex and striatum when participants correctly inhibit a response (Fig. 6b). A key objective for the ABCD study will be to examine how behavioral and neural correlates of impulse control and impulsivity change as a function of development and substance use and abuse.

3.3.3.3. The EN-back task

The EN-back task (Fig. 6, Cohen et al., 2016a, Cohen et al., 2016b) engages memory and emotion regulation processes and is a variant the HCP n-back task (Barch et al., 2013). The memory component of the n-back activates core brain networks relevant for working memory (Barch et al., 2013; Owen et al., 2005), providing evidence for its validity as a measure of working memory. It contains both high and a low memory load conditions (2 back and 0 back – see below) and the comparison of the two allows for the assessment of activation that is specifically associated with working memory as opposed to cognitive function more generally. This task shows reliable brain activations across subjects (Drobyshevsky et al., 2006) and time (Caceres et al., 2009). The task is sensitive to marijuana and alcohol use (Caldwell et al., 2005; Schweinsburg et al., 2005, Schweinsburg et al., 2008, Schweinsburg et al., 2010; Squeglia et al., 2011; Tapert et al., 2001, Tapert et al., 2004) is developmentally appropriate (Barch et al., 2013; Casey et al., 1995) and has been widely used in the field (Owen et al., 2005), providing generalizability to other studies. Finally, this task directly builds upon data collected as part of the lifespan pilot of the Human Connectome Project (Barch et al., 2013). The stimuli, unlike the traditional or HCP versions of the n-back task, include a set of happy, fearful and neutral facial expressions (Conley et al., 2017; Tottenham et al., 2009). Cognitive processing of these stimuli taps fronto-amygdala circuitry and functions involved in emotion reactivity and regulation (Hare et al., 2008; Gee et al., 2013), and taps ventral fronto-striatal circuitry implicated in reward (Somerville et al., 2011), providing evidence of its validity as a measure of emotion reactivity. Further, the ability to contrast neural faces to the happy and fearful faces allows for an assessment of the specificity of activation to emotionally evocative stimuli. These circuits have been implicated in addiction (Koob, 2003) and show adolescent-specific brain activations (Hare et al., 2008; Dreyfuss et al., 2014). The use of place stimuli as a non-emotional and non-social set of stimuli has been shown to produce highly reliable patterns of brain activity across subjects and time (Peelen and Downing, 2005). The facial stimuli are drawn from the NimStim emotional stimulus set (Tottenham et al., 2009) and the Racially Diverse Affective Expressions (RADIATE) set of stimuli (Conley et al., 2017) to adequately address the diversity among ABCD participants. The place stimuli are drawn from previous visual perception studies (Kanwisher, 2001; O'Craven and Kanwisher, 2000; Park and Chun, 2009).

The task includes two runs of eight blocks each. On each trial, participants are asked to respond as to whether the picture is a “Match” or “No Match.” Participants are told to make a response on every trial. In each run, four blocks are 2-back conditions for which participants are instructed to respond “match” when the current stimulus is the same as the one shown two trials back. There are also four blocks of the 0-back condition for which participants are instructed to respond “match” when the current stimulus is the same as the target presented at the beginning of the block. At the start of each block, a 2.5 s cue indicates the task type (“2-back” or “target=” and a photo of the target stimulus). A 500 ms colored fixation precedes each block instruction, to alert the child of a switch in the task condition. In this emotional variant of the task, blocks of trials consist of happy, fearful, and neutral facial expressions as well as places. Accuracy for the two memory load conditions (0- and 2-back) for each stimulus type (emotional faces, neutral faces, places) and across stimulus types, are the primary dependent measures.

Each block consists of 10 trials (2.5 s each) and 4 fixation blocks (15 s each). Each trial consists of a stimulus presented for 2 s, followed immediately by a 500 ms fixation cross. Of the 10 trials in each block, 2 are targets, 2–3 are non-target lures, and the remainder are non-lures (i.e., stimuli only presented once). There are 160 trials total with 96 unique stimuli of 4 different stimulus types (24 unique stimuli per type) are presented in separate blocks in each run. For the working memory component, the main contrast is a block design analyses contrasting 2-back and 0-back (8 blocks each). For secondary event-related analyses of target trials, there are 16 targets in the 2-back and 16 in the 0-back. In sum, there are 80 trials for each of the two memory load conditions, and 20 trials for each stimulus type in each of the two memory load conditions. Thus, 40 trials of each stimulus types (Fig. 7).

Fig. 7. Emotional N-Back Task. (Adapted from Barch et al.2013; Cohen et al., 2016a, Cohen et al., 2016b)

Preliminary behavioral data from the EN-back task (n = 965) indicate that most participants understood and could perform the task. The median accuracy is 0.82 and this level of performance is maintained across the two experimental runs (0.81 and 0.84, respectively, Fig. 8a) showing reliability in performance across the task. Accuracy was slightly better for the no memory load (0-back) condition than the memory load (2-back) condition with the median accuracy of 0.88 and 0.78, respectively. The relatively high level of mean accuracy for this age group on a difficult task is encouraging, since unlike the MID and SST, the Emotional n-back task does not individualize task difficulty.

Fig. 8. Preliminary results for the Emotional n-back task. A. Behavioral results. Boxplots provide the median, first and third quartiles for accuracy on the 0-back and 2-back conditions and for each experimental run of the task. B. fMRI results. Cortical (top) and subcortical (bottom) functional maps (signed Cohen’s d) for the contrast 2-back vs 0-back.

The preliminary imaging results (n = 517) on this task are consistent with the working memory literature (Fig. 8b). Specifically, fronto-parietal and fronto-thalamic activity previously associated with manipulation and maintenance of information in memory is observed for the main contrast of the 2-back vs the 0-back condition. A key question of the ABCD study will be how memory processes and the underlying neurocircuitry are impacted by chronic substance use during adolescence.

3.4. Post-scan assessments

3.4.1. Arousal questionnaire

Immediately following scanning, participants are administered the ABCD arousal state questionnaire again (see Supplemental Table 1), followed by an Emotional n-back Recognition Memory task (Supplemental Fig. 1) and a brief MID task questionnaire (Supplemental Table 2).

3.4.2. The EN-back recognition memory task

This task is a recognition memory test and a variant of the lifespan HCP task (http://www.humanconnectome.org/; Barch et al., 2013; Cohen et al., 2016a, Cohen et al., 2016b; Supplemental Fig. 1A). It measures short-term memory processes that tap hippocampal functioning (Stark and Okado 2003) implicated in substance use and abuse (De Bellis et al., 2000; Medina et al., 2007). The task includes 48 old stimuli presented during the emotional n-back task and 48 new stimuli, with equal numbers of each stimulus type in the old and new stimulus sets (12 each of happy, fearful, and neutral facial expressions as well as places in each set). A total of 96 pictures are presented during the recognition memory test. Participants are asked to rate each picture as either “Old” or “New.” Each picture is presented for 2 s followed immediately by a 1 s presentation of a fixation cross. Instructions and a 2-trial practice (one “Old” from the task practice and one new stimulus) precede the memory test. The task assesses memory for stimuli presented during the emotional n-back and takes approximately 5–10 min. Preliminary results (n = 868), suggest relatively low immediate recognition of specific stimuli, especially face stimuli at this age (Supplemental Fig. 1B).

3.4.3. The monetary incentive delay task post-scan questionnaire

This questionnaire asks the participant to rate how they felt when viewing the different cues and receiving the different outcomes during the MID task to determine the effectiveness and value of wins and losses (Supplemental Table 2). This questionnaire takes approximately 1–2 min. Previous reports of ventral striatal activation by reward anticipation on the MID task have correlated with individual differences in self-reported happiness about high-reward cues (Knutson et al., 2001).

4. Conclusions

The primary objective of the ABCD study is to create a unique data resource for tracking human brain development from childhood through adolescence to determine biological and environmental factors that impact or alter developmental trajectories. This article provides an overview of imaging procedures, instrumentation and protocol that have been harmonized across all 21 ABCD sites. Preliminary examination of behavioral and imaging data demonstrate feasibility and the developmental appropriateness of the procedures and protocol as well as generalizability of the findings to the existent literature.

The ABCD Study is based on an open science model. In partnership with the NIMH Data Archive (NDA), fast-track data containing unprocessed neuroimaging data and basic participant demographics (age, sex) has been released monthly since June 2017. The ABCD Study will release curated, anonymized data including all assessment domains annually, beginning February 2018 to the research community. Information on how to access ABCD data through the NIMH Data Archive (NDA) is available on the ABCD study data sharing webpage: https://abcdstudy.org/scientists_data_sharing.html . This open science model will allow scientists from all over the world to access and analyze the data with the goal of more rapid scientific discoveries that can enhance the well-being of youth and society.

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Introduction Neuroimaging facilitates the in vivo study of the developing human brain. The Adolescent Brain Cognitive Development (ABCD) study leverages this technology to investigate brain development from childhood to adolescence, aiming to identify biological and environmental influences on developmental trajectories. This large-scale study is tracking approximately 10,000 children aged 9–10 years across the United States, with a central focus on longitudinal measurements of brain structure and function. The ABCD Imaging Acquisition Workgroup has meticulously standardized measures and procedures across all 21 study sites to ensure data harmonization. This article outlines the rationale, overview, and preliminary quality assessments of the ABCD imaging protocol, highlighting its suitability for studying 9- and 10-year-old children. The ABCD study draws inspiration from numerous large-scale neuroimaging studies globally, which employ MRI to investigate brain structure and function in the developing brain. Notably, it builds upon advancements made by the Human Connectome Project (HCP), the Pediatric Imaging, Neurocognition, and Genetics (PING) Study, and aspects of the IMAGEN study, all of which have significantly contributed to our understanding of adolescent development. By integrating the knowledge gained from these pioneering studies, the ABCD study has established an optimized MRI acquisition protocol for measuring brain structure and function, harmonized across three 3T scanner platforms: Siemens Prisma, General Electric 750, and Philips. The protocol encompasses 3D T1- and 3D T2-weighted images, and diffusion-weighted images for assessing brain structure, as well as resting-state and task-based functional MRI for examining brain function. Task-based fMRI in the ABCD study employs three tasks: the Monetary Incentive Delay (MID) task, the Stop Signal Task (SST), and an emotional variant of the n-back task (EN-back). These tasks collectively assess six key functional domains: reward processing, motivation, impulsivity, impulse control, working memory, and emotion regulation, aligning with the original National Institutes of Health's (NIH) Collaborative Research on Addiction (CRAN) Request for Applications (RFA) guidelines. Table 1 provides a comprehensive overview of these domains, the corresponding tasks, cognitive processes involved, and associated neural correlates.

ABCD Materials and Methods A key objective of the study is to characterize developmental trajectories and neural signatures associated with adolescent mental health. To achieve this, the study aims for approximately 50% of the sample to exhibit early signs of externalizing and internalizing symptoms, enhancing statistical power to differentiate developmental pathways. Further details regarding the sample composition and overall design of the ABCD study are available in companion articles within this issue by Garavan et al., Loeber et al., and Volkow et al. Ethical considerations related to the study are thoroughly discussed in Clark et al. (this issue). This section details the imaging protocol, procedures, and tasks, with an emphasis on harmonization across all 21 ABCD sites.

Equipment and Software Scanner and Head Coil The ABCD imaging protocol is harmonized for use with three 3T scanner platforms (Siemens Prisma, General Electric (GE) 750, and Philips) equipped with multi-channel coils capable of multiband echo planar imaging (EPI) acquisitions. A standard adult-size head coil is employed across all sites and age groups for several reasons. First, the brain size of 9- and 10-year-olds is typically 90–95% of adult brain size, supporting the feasibility of using a standard stereotactic space. Second, employing age-specific coils would introduce significant analytical challenges by confounding coil type with age. Finally, custom coils necessitate manufacturer-specific customization, presenting logistical obstacles given the multi-site nature of the study and the importance of maintaining hardware stability throughout the 10-year duration. Stimulus Presentation and Response Collection Task-based fMRI necessitates specialized equipment and software for stimulus presentation and response collection. All ABCD fMRI tasks are programmed using E-Prime Professional 2.0 (version 2.0.10.356 or later) and are compatible with PC Windows 8.1 or earlier operating systems. Response collection is standardized across all tasks and sites using a Current Designs two-button response box, enabling precise measurement of response latency. Task instructions accommodate both left and right-hand dominance. Visual and auditory presentation equipment is not strictly standardized due to variability in scanner and control room configurations across sites and the absence of stringent visual or auditory resolution requirements for the fMRI tasks.

ABCD Scan Protocol Figure 1 depicts the ABCD neuroimaging protocol. The protocol was refined based on a multi-site pilot study involving 67 children and adolescents from diverse socioeconomic, racial, and ethnic backgrounds, including individuals considered at risk for substance abuse and mental health issues. Pilot data from over 30 participants revealed no significant differences in fatigue, as measured by fMRI task performance and self-report, between single-session and two-session scanning protocols, or between administering fMRI tasks at the beginning versus the end of the session. Consequently, scanning is conducted in either one or two sessions, providing flexibility for sites with limited scanner availability and accommodating the scheduling needs of participating families. Further supporting the feasibility of the protocol for 9–10 year olds, initial data from approximately 1000 participants indicate high scan completion rates (99% for the 3D T1-weighted scan; 88–98% for other scan types), with nearly 90% of participants completing all scan types across sites. Ordering of Scans The scan session follows a fixed order: localizer, 3D T1-weighted images, two runs of resting-state fMRI, diffusion-weighted images, 3D T2-weighted images, one or two additional runs of resting-state fMRI (depending on motion levels), and finally, task-based fMRI. Although the overall scan order is fixed, the order and version of the three fMRI tasks (MID, SST, and EN-back) are randomized across participants. This randomization mitigates potential order effects arising from the cognitively demanding nature of the fMRI tasks. Unlike the structural and resting-state scans, which require minimal participant engagement, the fMRI tasks demand sustained attention, response inhibition, working memory, and emotional reactivity. Randomizing task order helps control for potential performance fluctuations due to fatigue or carry-over effects of negative emotional processing. Furthermore, trial order within each task is pseudorandomized to minimize the impact of trial-by-trial processing demands. For the event-related MID and SST tasks, 12 optimized trial sequences were selected based on simulations to minimize variance in activation parameter estimates. This approach allows for assessing the generalizability of findings across task variants and controlling for sequence effects if necessary. Due to time constraints, the EN-back task employs a block design, given the number and level of factors and the requirement for instructed task switching between memory load conditions. Importantly, the randomly assigned task order and version at baseline are maintained for each participant's longitudinal scans, reducing within-subject variability and enhancing the ability to examine individual differences in developmental trajectories. To minimize within-family variability and facilitate the study of heritability and genetic effects, participants within a family receive the same task order and version.

Pre-scan Assessments and Training MR Screening Participants undergo a three-stage MR safety screening process: during initial recruitment, at scheduling, and immediately prior to the scan. The screening questionnaire assesses for contraindications to MRI, including braces, pacemakers, and other metallic implants or objects.

1. Future Directions and Challenges

While the ABCD study has made significant strides in understanding brain development during adolescence, several avenues for future research and challenges remain.

5.1. Longitudinal Follow-Up

Longitudinal data collection is crucial for elucidating developmental trajectories and identifying predictive biomarkers of mental health outcomes. The ABCD study plans to follow participants longitudinally through adolescence and into young adulthood, capturing critical periods of brain development and behavioral maturation. Longitudinal analyses will allow for the examination of individual differences in developmental trajectories, the impact of environmental exposures on brain structure and function, and the emergence of psychopathology.

5.2. Integration of Multimodal Data

The integration of multimodal data, including neuroimaging, genetics, cognitive assessments, and environmental measures, offers a comprehensive understanding of brain-behavior relationships. The ABCD study is well-positioned to leverage these data streams to unravel the complex interplay between genetic predispositions, environmental factors, and brain development. Integrated analyses will provide insights into the mechanisms underlying resilience or vulnerability to mental health disorders and inform targeted interventions.

5.3. Addressing Ethical and Privacy Considerations

As with any large-scale longitudinal study involving sensitive data, the ABCD study prioritizes ethical considerations and participant privacy. Robust data security measures are in place to protect participant confidentiality and ensure compliance with ethical guidelines. Moreover, transparent communication with participants and their families regarding data usage and privacy protections fosters trust and engagement in the study.

5.4. Enhancing Diversity and Representation

Efforts to enhance diversity and representation within the ABCD study are ongoing. By recruiting participants from diverse socioeconomic, racial, and ethnic backgrounds, the study aims to capture the heterogeneity of adolescent experiences and reduce disparities in mental health research. Culturally sensitive recruitment strategies and community engagement initiatives play a vital role in fostering inclusivity and equitable representation.

5.5. Advancing Computational Approaches

Advances in computational methods hold promise for extracting meaningful insights from large-scale neuroimaging datasets. Machine learning algorithms, network analysis techniques, and deep learning approaches enable the identification of complex patterns in brain structure and function. Integrating computational tools with neuroimaging data facilitates hypothesis generation, biomarker discovery, and personalized interventions tailored to individual risk profiles.

In summary, the ABCD study represents a pioneering effort to unravel the neurobiological underpinnings of adolescent development and mental health. Through rigorous methodology, collaborative partnerships, and a commitment to open science principles, the study aims to accelerate scientific discoveries and improve outcomes for youth worldwide. Continued investment in longitudinal research, interdisciplinary collaboration, and data sharing initiatives will pave the way for transformative discoveries in developmental neuroscience.

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Examining Brain Development: The ABCD Study Imaging Protocol

1. Introduction

Neuroimaging gives us a powerful way to look inside the living, developing human brain. The ABCD study uses this tool to follow about 10,000 children across the United States, starting from ages 9-10, to understand how their brains change throughout adolescence. This massive project aims to identify both biological and environmental factors that influence these changes. To ensure consistent and high-quality data across its 21 research sites, the ABCD Imaging Acquisition Workgroup carefully selected and standardized the brain imaging techniques and procedures. This article explains the rationale behind these decisions and provides an overview of the imaging protocol, along with early quality checks that confirm its suitability for studying brains in this age group.

Large-scale brain imaging studies are transforming our understanding of the developing brain. The ABCD study builds upon pioneering work done by projects like the Human Connectome Project (HCP), the Pediatric Imaging, Neurocognition, and Genetics (PING) Study, and the IMAGEN study. These projects have laid the groundwork for the advanced brain imaging techniques used in the ABCD study.

Learning from these earlier studies, the ABCD team created an optimized protocol for measuring brain structure and function. This protocol is designed to work seamlessly across three major MRI scanner brands (Siemens, General Electric, and Philips) at all 21 ABCD sites. The protocol includes:

• Structural MRI: 3D T1-weighted and T2-weighted images, and diffusion-weighted images to map the brain's physical components and connections.

• Functional MRI (fMRI): Resting-state and task-based fMRI to observe brain activity patterns, both at rest and during specific cognitive challenges.

Three tasks are used during fMRI to assess how different brain regions work together:

1. Monetary Incentive Delay (MID) Task: Investigates reward processing, motivation, and decision-making in the context of potential gains and losses.

2. Stop Signal Task (SST): Measures impulsivity and the brain's ability to control impulsive actions.

3. Emotional N-back (EN-back) Task: Assesses working memory (the ability to hold and manipulate information in mind) and how emotions influence this capacity.

These tasks were chosen because they target six key areas of brain function relevant to adolescent development and the potential for addiction. Table 1 summarizes the tasks and the specific brain functions they measure.

Table 1. Domains of function measured by the ABCD fMRI tasks.

2. ABCD materials and methods

A crucial goal of this research is to map typical developmental pathways and identify patterns in the brain that signal vulnerability to mental health challenges during adolescence. To do this effectively, about half of the participants were selected because they showed early signs of difficulties with emotional regulation or behavioral control, placing them at higher risk for substance use and other mental health issues. This article focuses specifically on the imaging protocol and procedures, but other articles in this issue provide more details about the study design and ethical considerations.

2.1. Equipment and software

2.1.1. Scanner and head coil

The ABCD imaging protocol was carefully harmonized for use with three 3T MRI scanner models: Siemens Prisma, General Electric (GE) 750, and Philips. All scanners use specialized head coils that allow for faster imaging, particularly for fMRI. A standard adult-sized coil is used for all participants, even though their brains are still developing. This decision was based on several factors:

• Brain size in 9- and 10-year-olds is typically 90-95% of adult size, and research supports the use of a common spatial reference frame for this age range.

• Using different coils for different ages would make data analysis much more complex, as the type of coil would be directly related to age.

• Custom coils require significant manufacturer involvement, which would have been challenging to coordinate across all 21 sites, especially considering the need for stable hardware throughout this 10-year study.

2.1.2. Stimulus presentation and response collection

The task-based fMRI scans rely on specific equipment and software to present stimuli to participants and record their responses. All tasks are programmed using E-Prime Professional software and are compatible with Windows computers. The tasks and stimuli themselves are publicly available for other researchers to use. To ensure consistent measurement of response times across tasks and sites, a standardized two-button response box from Current Designs is used. Participants respond with their dominant hand. While visual and auditory presentation systems are not strictly standardized, the software is designed to accommodate variations in equipment setups across sites.

3. ABCD scan protocol

Figure 1 illustrates the sequence of scans within the ABCD imaging protocol.

[Image of ABCD Neuroimaging Protocol: Localizer, 3D T1, rs-fMRI (2 runs), Diffusion, 3D T2, rs-fMRI (1-2 runs), Task fMRI (Randomized order: MID, SST, EN-back)]

Fig. 1. ABCD Neuroimaging Protocol.

3.1. Ordering of scans

The scan session follows a fixed order:

1. Localizer: A quick scan to help position the brain for subsequent images.

2. 3D T1-weighted Images: Provides detailed anatomical information.

3. Resting-state fMRI (2 runs): Measures brain activity while the participant rests quietly.

4. Diffusion-weighted Images: Maps the brain's white matter connections.

5. 3D T2-weighted Images: Complementary to T1, useful for detecting abnormalities.

6. Resting-state fMRI (1-2 runs): More resting-state data, with the number of runs determined by head motion during the first set.

7. Task-based fMRI: The order of the three fMRI tasks (MID, SST, EN-back) is randomized for each participant to prevent order effects.

This fixed order helps ensure consistency across sites, but the protocol can be split into two sessions if needed. Flexibility in scheduling makes it easier for families to participate. The high scan completion rates from the first 1000 participants (nearly 90% completed all scan types) suggest that this approach has been successful.

3.2. Pre-scan assessments and training

3.2.1. MR screening

Participants are screened for MRI contraindications (e.g., metal implants, pacemakers, braces) at three points: during initial recruitment, when scheduling the scan, and again right before the scan session.

3.2.2. Simulation and motion compliance training

Before entering the actual MRI scanner, participants go through a simulation to familiarize themselves with the environment and practice staying still. Mock scanners, recordings of scanner sounds, or play tunnels mimicking the scanner bore help reduce anxiety. Motion is a major challenge in pediatric imaging, so behavioral training techniques and motion-tracking devices (e.g., simulators, modified gaming systems) are used to teach children how to minimize head movement during the scan.

3.2.3. Arousal questionnaire

Right before the scan, participants complete a questionnaire about their current state of alertness and mood. This questionnaire is repeated after the scan to track any changes. The participant then receives earplugs, lies down on the scanner bed, and is fitted with a breathing belt and a pulse oximeter to monitor physiological signals. Foam padding around the headphones helps further stabilize the head.

3.3. Scan session

A child-friendly movie plays as the participant enters the scanner and continues during the localizer, T1, T2, and diffusion scans. During resting-state fMRI, participants keep their eyes open and focus on a crosshair on the screen. For the task-based fMRI, the movie is replaced with the specific instructions and stimuli for each task.

3.3.1. Scanning parameters

The imaging parameters are optimized for each scanner model and are summarized in Table 2. This ensures that every ABCD site can use the same standardized protocol, reducing the chance of errors. Images are acquired in a specific orientation to minimize image artifacts and potential discomfort for the participant.

Table 2. ABCD harmonized imaging scanning parameters for Siemens Prisma, Phillips, and GE 750 3T scanners.

[Table with detailed scanning parameters for each scanner model and scan type]

Each type of scan provides unique information about the brain:

• 3D T1-weighted Images: Used to define the brain's structure, including the cortex (outer layer) and subcortical regions (deeper structures).

• 3D T2-weighted Images: Useful for detecting white matter lesions (areas of damage) and measuring cerebrospinal fluid.

• Diffusion-weighted Images: Map the brain's white matter tracts, which act like communication pathways between different brain regions.

• Resting-state fMRI: Reveals how brain activity is organized and synchronized across different regions while at rest.

• Task-based fMRI: Shows how brain activity changes in response to specific cognitive demands.

3.3.2. Motion detection and correction

Minimizing head motion during scanning is crucial, especially for fMRI. The ABCD study uses real-time motion detection and correction techniques whenever possible. For anatomical scans (T1 and T2), these techniques involve tracking the participant's head position and adjusting the scan parameters on the fly. For resting-state fMRI, a system called FIRMM helps monitor motion and allows technologists to collect additional data if needed.

Preliminary data from over 2500 participants are encouraging:

• Mean head motion during resting-state fMRI is 0.22 mm.

• Mean motion during task-based fMRI is even lower, ranging from 0.25 to 0.28 mm depending on the task.

These low motion levels are impressive given the young age of the participants and the length of the scans. It's important to note that a significant portion of the participants have risk factors that might make it harder for them to lie still, highlighting the effectiveness of the training procedures.

3.3.3. The fMRI tasks

Each fMRI task is designed to activate specific brain networks and provide insights into how those networks function in this age group.

3.3.3.1. Monetary Incentive Delay Task (MID)

The MID task (Figure 2) measures brain activity related to:

• Anticipating and Receiving Rewards/Losses: How does the brain respond when there's a chance to win or lose money?

• Motivation: How much effort will participants put in to succeed?

[Image of the MID task: Cue (e.g., +$1.00), Anticipation, Target, Feedback (e.g., You Won!)]

Fig. 2. Monetary Incentive Delay task. (Adapted from Knutson et al., 2001)

Key features of the MID task:

• Participants see cues indicating potential wins or losses, followed by a brief period of anticipation.

• They then need to respond quickly to a target to try to win money or avoid losing money.

• The difficulty of the task adjusts based on performance to ensure everyone succeeds about 60% of the time. This keeps motivation levels consistent.

Preliminary data from 965 participants show that this approach is working as intended, with hit rates hovering around 60%. The imaging data are also promising, with robust activation observed in the ventral striatum and medial prefrontal cortex—regions known to be involved in reward processing—when participants experience a win.

3.3.3.2. The Stop Signal Task (SST)

The SST (Figure 3) assesses the brain's ability to inhibit impulsive actions, a crucial skill that develops throughout adolescence:

• Go Trials: Participants respond as quickly as possible to an arrow pointing left or right.

• Stop Trials: On a subset of trials, a "Stop Signal" appears after the arrow, instructing the participant to try to withhold their response.

[Image of the SST: Go Trial (arrow, fixation), Stop Trial (arrow, Stop Signal, fixation)]

Fig. 3. Stop Signal task. (Adapted from Helfinstein and Poldrack, 2012)

Key features of the SST:

• The timing of the "Stop Signal" adjusts based on performance, ensuring participants successfully stop themselves on about half of the "Stop" trials.

• This individualized difficulty level allows researchers to estimate each participant's stop signal reaction time (SSRT), a measure of their inhibitory control ability.

Early behavioral results suggest that the task is working as expected, with stop-error rates close to 50%. Initial analyses of the imaging data show strong activation in the lateral prefrontal cortex, anterior cingulate cortex, and striatum—regions linked to cognitive control and response inhibition—during successful stops.

3.3.3.3. The EN-back Task

The EN-back task (Figure 4) taps into two key aspects of cognitive function:

• Working Memory: The ability to hold and manipulate information in mind.

• Emotion Regulation: How well we can control our thoughts and actions in the face of emotional distractions.

[Image of the EN-back task: Instruction (e.g., "2-Back: Faces"), Target (face), Trial sequence (different faces), Response options ("Match", "No Match")]

Fig. 4. Emotional N-Back Task. (Adapted from Barch et al., 2013; Cohen et al., 2016a, Cohen et al., 2016b)

Key features of the EN-back:

• Participants see a series of images (faces and places) and are instructed to indicate whether the current image matches one presented earlier in the sequence.

• The task has two difficulty levels:

  • 0-back (easy): The match is always the image presented at the beginning of the block.

  • 2-back (hard): The match is the image shown two trials back, requiring more working memory.

This task is particularly interesting because it uses emotionally evocative stimuli (happy, fearful, and neutral faces). This allows researchers to examine how emotional content influences working memory performance and the brain regions involved.

Preliminary data from the EN-back show that participants are generally successful on this challenging task, with a median accuracy of 82%. As expected, the 0-back condition was slightly easier than the 2-back condition. The imaging data are also consistent with previous research, showing increased activity in frontoparietal and frontothalamic networks—critical for working memory—during the more demanding 2-back condition.

3.4. Post-scan assessments

After completing the scans, participants engage in a few final activities:

3.4.1. Arousal questionnaire

The arousal questionnaire, administered before the scan, is given again to assess any changes in alertness or mood after the scanning session.

3.4.2. The EN-back recognition memory task

To further probe memory processes, participants complete a recognition memory test for the images presented during the EN-back task. This task involves distinguishing between images seen during the task (old) and new images. This helps researchers understand how well participants encoded the images into memory during the task itself.

3.4.3. The MID post-scan questionnaire

Participants are asked to rate how they felt during different parts of the MID task, specifically when they saw the cues signaling potential wins and losses and when they received feedback about their performance. This helps measure the subjective experience of reward and loss, complementing the brain activity data from the MID task.

4. Conclusions

The ABCD study aims to create a valuable resource for understanding brain development and the factors that shape it. This article described the standardized imaging protocol used across all 21 ABCD sites. Early analysis of behavioral and imaging data indicates that the procedures are appropriate for this age group and produce reliable results.

The ABCD study embraces open science principles, meaning that data are regularly shared with the scientific community. This open access allows researchers worldwide to explore this rich dataset, accelerating discoveries that could benefit children and adolescents everywhere.

Link to Article

1. Introduction

Scientists use brain scans to see how the brain grows and changes. The ABCD study is trying to learn how our brains grow from childhood to adulthood and what things can affect that. They are studying about 10,000 kids in the US, all aged 9–10 at the start, and taking brain scans each year to see how their brains change. This article talks about how they take those scans and how well it’s working so far.

Lots of other studies have used brain scans to study how our brains work. The ABCD study is learning from these past studies, especially the Human Connectome Project, the Pediatric Imaging, Neurocognition, and Genetics (PING) Study, and the IMAGEN study. By building on these past studies, they created a plan to study the brain that works across all 21 ABCD locations and three different brands of brain scanners (Siemens, General Electric, and Phillips). The plan includes different types of scans: some show the parts of the brain (like the cortex, which is the outer layer, and deeper parts), and others show how the brain works when it’s resting or doing a task.

The ABCD study uses three tasks during their brain scans to see how the brain works: the Monetary Incentive Delay (MID) task, the Stop Signal task (SST), and the Emotion n-back task (EN-back). These tasks let scientists look at six important ways our brains work, all of which are affected by drugs and alcohol:

• How we respond to rewards

• What motivates us

• How impulsive we are

• How good we are at controlling our impulses

• Working memory

• How we control our emotions

2. Materials and methods of the ABCD study

One important goal of the ABCD study is to figure out how the brain changes during adolescence, especially in a way that leads to mental health problems. To do this, they are making sure that about half of the kids in the study have some early signs of problems controlling their emotions or behavior. You can find out more about how the ABCD study chose the kids for their study in the articles by Garavan, Loeber, and Volkow.

2.1. Equipment and software

2.1.1. Scanner and head coil

The brain scanner has a big magnet and a piece that fits over the head, called a coil. The ABCD study decided to use the same size coil on all of their scanners, even though kids’ heads are smaller than adults. They did this for three reasons. First, the brains of 9- and 10- year olds are almost the same size as adult brains. Second, if they used different coils for kids of different ages, the coil would affect the scan, making it harder to see how the brain changes as kids grow. Third, getting different coils for each scanner would have been too difficult.

2.1.2. Stimulus presentation and response collection

The brain scans that involve tasks need a way to show things to the kids in the scanner and record their answers. All of the ABCD tasks are programmed using special software called E-Prime. Kids press buttons to answer the questions during the tasks. The buttons are all from the same company to make sure that the timing of their answers is correct. What kids see and hear during the tasks is different at each site, but all sites make sure that kids can clearly see and hear everything.

3. The ABCD scan protocol

Figure 1 shows the steps involved in the ABCD brain scan. Researchers tested out this process with a smaller group of kids first and found that it worked well to do all the scans in one day. But, to be flexible, kids can do the scans in one or two sessions.

3.1. Ordering of scans

Each scan session starts by taking pictures of the brain at rest and then having the kids do the tasks. Although every kid does the same types of scans, the order of the tasks is different for each kid. The researchers decided to do this because the tasks require a lot of brainpower, and they wanted to make sure that doing one task didn’t make the kids tired and affect how they did on the next task. This helps to control for something called “order effects.” They also change the order of the questions within each task. This helps to make sure that the way kids answer one question doesn’t affect how they answer the next question.

The specific order of tasks and questions is the same each time a kid gets scanned. This reduces the chances that differences in the brain scans over time are due to differences in the tasks or questions. It also makes it easier to see how a kid’s brain changes over time. Finally, kids in the same family do the tasks and questions in the same order so that the researchers can study how genes affect the brain.

3.2. What happens before the scan

3.2.1. MR screening

Before the scan, kids fill out a questionnaire to make sure that it’s safe for them to be in the MRI machine. For example, kids with braces, pacemakers, or certain types of metal in their body can’t get an MRI. Kids actually fill out this safety questionnaire three times: when they first sign up for the study, when they schedule the scan, and right before the scan.

3.2.2. Simulation and motion compliance training

Since the scanner is like a small tunnel, kids get a chance to try out a pretend scanner first. This helps them get used to what it looks and sounds like when they’re in the real scanner. Kids also learn how to keep their heads still while they’re in the scanner because even small movements can affect the scan.

3.2.3. Arousal questionnaire

Right before going into the scanner, kids use the bathroom and then answer questions about how alert they’re feeling. They will answer these questions again after the scan. Once in the scanner, kids get earplugs, a breathing monitor, and a heart rate monitor. The researchers also put foam pads around the headphones to help keep their heads still. Then, they watch a movie while they get their brain scanned.

3.3. Scan session

Kids continue to watch a movie while the first few brain scans are taken. Then, they do the tasks.

3.3.1. Scanning parameters

Each type of scan provides different information about the brain. Some scans measure the size and shape of the brain, while others measure how active different parts of the brain are.

3.3.2. Motion detection and correction

It is really important for kids to hold their heads as still as possible during the scan. The ABCD scientists use special techniques to minimize and correct for any head movements.

Scientists are especially worried about head movements during the resting state scan. Preliminary data from over 2,500 kids show that the average head movement during this scan is very small, less than ¼ of an inch! This is really good, especially given that the scans take a long time, and many kids in the study have problems with attention or behavior.

3.3.3. The fMRI tasks

Now let's dive deeper into the three tasks that kids do during the brain scan!

3.3.3.1. Monetary Incentive Delay Task (MID)

In the MID task, kids can win or lose money depending on how fast they press a button after seeing a target. This helps researchers see which parts of the brain are involved in reward, motivation, and quick thinking (Figure 2). [Important: Do not include Figure 2, as it is redundant with Figure 3]. A lot of research has shown that the MID task is a good way to study the brain, and these studies have shown that:

• This task activates the reward center of the brain.

• The brain responds differently to this task at different ages.

• People who use drugs and alcohol respond differently to this task.

• People respond similarly to the task each time they do it.

In the MID task, kids see a picture that tells them how much money they could win or lose and then have to press a button quickly when they see a target. The amount of time they have to press the button changes depending on whether they responded quickly enough on the previous trial. This helps to make sure that kids are successful on about 60% of the trials.

Early results from the ABCD study suggest that this method of adjusting the task difficulty is working well! Most kids are successful on about 60% of trials, and they earn about $21 on average. These results are similar to what other researchers have found.

3.3.3.2. The stop signal task (SST)

The SST requires kids to press a button when they see an arrow but to stop pressing the button if they hear a beep after the arrow (Figure 5). [Important: Do not include Figure 5, as it is redundant with Figure 6]. This task helps researchers study self-control and impulsivity.

The SST is a good way to study the brain. Here's what we know based on past research:

• This task activates parts of the brain involved in controlling our behavior.

• Kids, teenagers, and adults respond differently to this task.

• People who use drugs and alcohol respond differently to this task.

The time between the arrow and the beep changes throughout the task. The time gets longer if the child successfully stops after the beep and shorter if they aren’t able to stop. This helps to make sure that kids are successful on about 50% of the trials.

Early results from the ABCD study show that this method of adjusting the task difficulty is working because most kids can stop about half the time. The results also show that kids get better at stopping their response over time, and they are very accurate at pressing the button when there isn’t a beep.

3.3.3.3. The EN-back task

The EN-back task requires kids to remember whether they’ve seen a picture before. The task has two parts: in the first part (0-back), they have to remember whether the picture is the same as one they just saw. In the second part (2-back), they have to remember whether the picture is the same as one they saw two pictures ago (Figure 6). This helps researchers study working memory and how we process emotions.

The EN-back task is another good way to study the brain, and it builds upon tasks used in previous studies. Here's why it's so useful:

• This task activates parts of the brain involved in working memory.

• Kids, teenagers, and adults respond differently to this task.

• People who use drugs and alcohol respond differently to this task.

• This task is similar to one used by the Human Connectome Project.

Early results from the ABCD study show that kids can do the task, remembering about 82% of the pictures, on average, and that their memory is a bit worse when they have to remember what they saw two pictures ago.

3.4. What happens after the scan

3.4.1. Arousal questionnaire

Right after the scan, kids answer the same questions about how alert they are feeling as they did before the scan. Then, they do two short tasks to test their memory.

3.4.2. The EN-back recognition memory task

In this task, kids see pictures of faces and places and have to decide whether they saw each picture during the EN-back task. This task takes about 5–10 min, and it helps researchers study a part of the brain called the hippocampus, which is involved in memory and is affected by drug use.

3.4.3. The monetary incentive delay task post-scan questionnaire

This questionnaire asks kids to rate how they felt when they were doing the MID task, like how happy or sad they felt when they won or lost money.

4. Conclusions

The ABCD study is trying to learn how our brains grow and change during adolescence. This article describes the procedures and tasks used in the study, and early results suggest that it’s working well! The scientists are sharing their results with other researchers, which will help everyone learn more about the brain!

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Scientists use special pictures of the brain to learn how it grows and changes. The ABCD study is a big research project that is looking at the brains of kids! The goal of the study is to see how their brains change as they grow up and figure out what helps brains grow in the best way. Around 10,000 kids from all over the United States are in this study.

Lots of scientists are working together to learn from these brain pictures. One group, called the ABCD Imaging Acquisition Workgroup, decided how to take the pictures and what to look for. They make sure that all the scientists are studying the same things. This article explains what happens when they get their brain pictures taken for the ABCD study. How do they look at brains? Scientists use a special machine called an MRI to take pictures of the brain. It's a little bit like a giant camera that can see through their head!

Lots of other studies are using MRIs to learn about how children's brains work, like the Human Connectome Project (HCP) and the Pediatric Imaging, Neurocognition, and Genetics (PING) Study. The ABCD study uses three different types of MRI machines. No matter which machine is used, it takes special pictures that show different parts of the brain. Some pictures show the brain's shape, and others show how it works.

The ABCD study also wants to know how their brain works when they do different things. To do this, they'll play some fun games while they're in the MRI machine! These games will test how they think, how they control themselves, and how they feel.

Getting Their Brain Pictures Taken

Before they get their brain pictures taken, they'll get to see what the MRI machine looks like and hear what it sounds like. This will help them feel comfortable when it's time for their real brain pictures. They'll also practice the games they will play during the scan. When they're ready, they'll lie down on a comfy bed that slides into the MRI machine. The machine will make some noises, but don't worry, it's just doing its job! They can wear earplugs if they want. The most important thing is to hold very still while the machine is taking pictures of their brain. The scientists want to see how their brain works when they're resting and when they're doing the games. First, they'll get to relax and watch a movie while the machine takes pictures. Then, they'll play the games.

Playing Games in the MRI Machine

Here are the games they'll play while they're in the MRI machine:

The Money Game: In this game, they can win or lose money by pressing a button when they see a target.

The Stop Game: They will see arrows pointing left and right, and they need to press the button that matches the direction. Sometimes, though, they'll need to stop themselves from pressing the button. This game helps scientists see how well they can control themselves.

The Memory Game: They will see pictures of faces and places. They have to remember if they've seen the picture before. This game helps scientists see how well they can remember things.

What Happens After the Scan?

After their brain pictures are taken, they'll take a quick test to see how well they remember the pictures from the Memory Game. They'll also answer some questions about how they felt while they were playing the games.

Conclusion

The ABCD study is helping scientists learn so much about how children's brains grow and change. By taking pictures of their brain and seeing how they play games, scientists can learn what helps brains grow in the best way possible. This will help keep kids' brains healthy and strong as they grow up. All of the pictures and information from the study will be shared with other scientists so that everyone can learn from it.

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