Introduction

Adolescence is the period of physical, cognitive, and social maturation between childhood and adulthood [Lerner and Steinberg, 2004; Sisk and Foster, 2004]. The beginning of adolescence occurs around the onset of puberty and is therefore marked by dramatic changes in hormone levels and in physical appearance (including rapid physical growth, changes in facial structure, and the appearance of secondary sexual characteristics). Over the same interval, adolescents experience numerous changes in social, academic, and other environmental influences, and typically enter a stage of profound psychological transition. The end of adolescence is said to occur when an individual has attained a stable adult role, by which time the majority of pubertal transitions will have reached completion, at least in industrialized nations [Choudhury, 2010; Lerner and Steinberg, 2004]. Throughout adolescence, there are changes in the structure and function of the brain. Sexual dimorphisms in many of these changes suggest possible relationships to puberty.

Relatively little is known about the relationship between puberty and neural development in humans. However, a wealth of evidence from nonhuman animal studies indicates that the hormonal events of puberty exert profound effects on brain maturation and behavior [Cahill, 2006; Sisk and Foster, 2004; Spear, 2000]. These changes mould the perceptions, motivations, and behavioral repertoire of an individual, enabling reproductive behavior and independence [Sato et al., 2008]. In recent years, a small but growing number of human behavioral and neuroimaging studies, including in populations with endocrine disruptions, have provided tentative evidence that pubertal hormones might influence the structure and function of the developing human brain.

Puberty: The Beginning Of Adolescence

Early adolescence is characterized by changes to the body as a result of puberty, which comprises three endocrine events: adrenarche, gonadarche, and activation of the growth axis [Dorn, 2006; Spear, 2000]. Gonadarche, which is often taken to constitute puberty per se, is a biological process beginning with activation of the hypothalamic-pituitary-gonadal axis and ending with the attainment of reproductive competence. This process usually begins between ages 8 and 14 years in females (mean age 11), and between ages 9 and 15 in males (mean age 12), in response to pulsatile release of gonadotropin-releasing hormone (GnRH) from the hypothalamus, which stimulates pituitary production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). LH and FSH activate maturational changes in the gonads (ovaries or testes), which respond by attaining reproductive capacity (producing gametes). The maturing ovaries and testes also secrete the gonadal steroids estrogen and testosterone, respectively. These increases in gonadal steroids in turn trigger additional changes in the reproductive organs, and the appearance of secondary sexual characteristics [Susman and Rogol, 2004].

Adrenache, or activation of the hypothalamic-pituitary-adrenal axis, often begins earlier than gonadarche, typically between ages six and nine in females, and a year later in males [Dorn, 2006; Grumbach and Styne, 2003]. Adrenal androgens (weaker forms of gonadal testosterone) begin to rise at the start of adrenarche and continue to increase until they reach a peak in the early 20s [Worthman and Stallings, 1997]. These increases in adrenal androgens contribute to the development of secondary sexual characteristics such as axillary and pubic hair and changes in sweat glands/body odor. It is possible that adrenarche also gives rise to maturational effects that begin prior to the period usually considered as adolescence; however, these effects are not well understood [Dorn, 2006].

The third hormonal event that occurs during puberty is activation of the growth axis, resulting in a linear growth spurt at around age 12 in girls and age 14 in boys, as well as changes in body size and composition [Marshall and Tanner, 1969, 1970].

Hormonal Effects On Brain And Behavior

The gonadal steroid hormones estrogen and testosterone, as well as their weaker adrenal counterparts, influence the physical appearance of the body. They also affect the brain and behavior. These effects are hypothesized to occur via two relatively distinct processes: organization and activation [Schulz et al., 2009; Sisk and Foster, 2004]. Organizational effects occur pre- and perinatally, with waves of testosterone masculinizing and defeminizing neural circuits in males, and the absence of testosterone resulting in a female neural phenotype. Activational effects occur at puberty, as gonadal steroid hormones act on dormant neural circuits to elicit adult reproductive behaviors in context; a recent modernization of this dichotomy suggests that the hormonal events of puberty also organize neural circuits for adult social and reproductive behaviors [Schulz et al., 2009; Sisk and Foster, 2004]. Indeed, based on findings from nonhuman animal studies, it is suggested that the hormonal events of puberty trigger a second period of structural reorganization and plasticity in the brain [Sisk and Foster, 2004]. In humans, however, there is very little understanding of the specific relationships between puberty and adolescent brain development.

Animal studies indicate that sex steroid hormones exert three main effects on behavior at puberty, via specific brain structures. The first effect is the facilitation of directly reproductive behaviors, which occurs mainly via the hypothalamus. The second effect is via the reorganization of sensory and association regions of the brain, including visual cortex [Nunez et al., 2002], amygdala, and hippocampus [Hebbard et al., 2003; Romeo and Sisk, 2001; see also Shen et al., 2010]. This results in altered sensory associations, e.g. to the smell or sight of potential sexual partners or competitors [Sisk and Foster, 2004], which may facilitate some attentional and motivational changes at puberty. The third effect of puberty hormones occurs via reward-related brain structures such as the nucleus accumbens, and dopaminergic pathways to the prefrontal cortex. These effects are necessary for establishing strong motivation to seek out reproductive opportunities. For example, in the rodent nucleus accumbens, pubertal increases in testosterone remodel neural circuits influencing motivation toward reward-seeking behaviors, including sexual behavior [Sato et al., 2008]. It is possible that adrenarchel hormones (DHEA and DHEAS) begin to exert similar effects on brain and behavior prior to the onset of gonadarche, but these effects are poorly understood. There is clearly a need for more research focusing on the earliest stages of puberty/adrenarche to advance understanding of these aspects of puberty and adolescent brain development and behavior [see Dorn, 2006; for discussion].

Measuring Puberty In Studies Of Adolescent Brain Development

Relatively little is known about puberty-specific changes in human brain development. Advancing understanding in these areas will require careful attention at two levels: conceptually and methodologically. Conceptually, this will require the development and refinement of models of adolescent brain development that address specific aspects of pubertal maturation (e.g. specific hormones) that are causally linked to specific aspects of brain and behavioral changes. Methodologically, it will require studies that are designed with the selection of samples and measures of puberty that permit testing of these specific hypotheses. Because age and pubertal maturation are often correlated (and age is easily measured with great precision and validity, while puberty is often estimated with rough categorical measures that are not easily validated), there is a need for studies with designs that explicitly disentangle puberty and age effects (e.g. recruiting samples that are the same age and grade level but differ on pubertal maturation, and then restudying longitudinally).

These goals raise a number of issues regarding how to measure specific aspects of pubertal maturation in human studies. For a start, puberty is neither a brief event nor a unitary phenomenon, but instead, comprises several distinct but temporally-overlapping processes that extend over several years [Dorn, 2006]. As described earlier, these processes include activation of adrenal, gonadal, and growth hormone systems, and in addition a variety of direct and indirect effects, from growth spurts to changing self-image. The most appropriate measure of puberty will therefore depend in part on the specific research question in each study.

A commonly used measure of puberty is Tanner Stage. Tanner staging categorizes individuals along an ordinal puberty scale from 1 to 5, on the basis of pubic hair and breast development in females, and pubic hair and genital development in males [Tanner, 1971; Tanner and Whitehouse, 1976]. Tanner staging by physical exam should be carried out by a trained clinician. There are several limitations to Tanner staging. The scale was developed with reference to a single ethnic group (there may be cross-ethnic differences) and in a relatively small sample of 200 children. Overweight girls will tend to be inaccurately staged, due to the reliance of the staging on breast development, which can be erroneously over-estimated in a purely visual examination. Despite these limitations, Tanner staging has historically been considered the gold standard for puberty measurement [Dorn, 2006].

In light of the above-mentioned concerns, it might be expected that Tanner staging by physical examination could be usefully supplemented by hormonal assays, since these measure adrenal and gonadal (or adrenal/gonadal-releasing) hormones upstream from their external physical effects. Hormone assays may be increasingly useful for measuring pubertal stage in the future; however, at the present time it is unclear how hormone measurements should be combined with (or used in conjunction with) other measures such as Tanner stages [see Shirtcliffe et al., 2009]. There are also other practical issues regarding hormonal measures, including cost, subject burden, and the fact that levels of different puberty hormones fluctuate in monthly and circadian cycles. Little research has been done comparing hormone levels in different biological samples (saliva, blood, urine) with clinician-assessed Tanner stages [see Dorn, 2006; Shirtcliffe et al., 2009], so it is unclear how much weight should be given to hormone levels. At a conceptual level, for example, some neurobehavioral changes at puberty may be the direct result of increasing hormone levels on specific neural systems during adolescent brain development (and thus best quantified by hormone measures) while other neurobehavioral changes may reflect more complex influences (e.g. changes in social experience that are more directly tied to the physical changes and social roles, and better linked to Tanner stages than any specific hormone change).

Tanner staging by physical examination by a qualified clinician can raise practical issues regarding appropriateness and convenience. Often this is best accomplished in the context of doing a brief “health” exam. That is, Tanner staging can be part of a normal physical health exam and therefore should not be associated with any stigma or ethical concerns (beyond a normal physical health check). However, the cost (clinician time, special room and equipment for a physical exam, and explaining the procedures to the adolescent and family) can make this impractical for many research studies. Therefore, it is valuable to consider alternative ways to quantify pubertal maturation, such as assessments by self-report questionnaire. A relatively large number of studies have assessed self-rated (or parent-rated) Tanner stage using the Petersen Development Scale [PDS; Petersen et al., 1988]. This is a questionnaire that includes items assessing hair growth, skin changes, and growth spurt, with sex-specific items i.e. menarche and breast development in females, and genital growth and facial hair in males. As such, the PDS measures a composite puberty score that includes the effects of adrenal and growth hormones, as well as gonadal hormones. Correlations with clinician-assessed Tanner stage are not especially high: one study found correlations between 0.61 and 0.67 in 11- to 13-year-old girls for the self-report PDS [Brooks-Gunn et al., 1987; correlations are even lower for parent-report PDS; see Shirtcliffe et al. 2009]. The extent to which these relatively low correlations are due to inaccurate self-rating, or to distinct constructs, such as the distinct effects of adrenal/growth versus gonadal hormones, needs to be evaluated. The PDS can be used with caution to estimate Tanner stage when a physical examination is not possible. However, if the research question does not concern hormone levels and Tanner stage, but instead relates to self-image and self-consciousness, or to puberty stage relative to peers, it can be argued that the PDS is the most relevant measure [see Dorn, 2006 for discussion]. In summary, researchers should give ample consideration to which aspect of puberty is most relevant to their research question and select their measures of puberty (and overall design of the study) accordingly.

Puberty And Structural Brain Development As Measured By MRI

The advent of noninvasive brain imaging techniques, in particular magnetic resonance imaging (MRI), has enabled investigation of the development of the living human brain. Developmental changes that have been delineated using MRI include alterations in the amount of gray and white matter, and changes in white matter microstructure.

Adolescent Gray Matter Development

The amount of cortical gray matter (its density, volume, and thickness) changes during childhood and adolescence in a region-specific and predominantly nonlinear manner [Giedd et al., 1999; Shaw et al., 2008; Sowell et al., 1999; Tamnes et al., 2009; see e.g. Blakemore, 2008 for review]. Across much of the cortical surface, gray matter development conforms to an inverted-U shaped developmental trajectory, initially increasing in volume during childhood, reaching a peak in adolescence, and declining steadily into adulthood. Gray matter is composed of the cell bodies, dendrites and nonmyelinated axons of neurons, as well as glial cells and capillaries. Therefore, and based on evidence from histological samples [e.g. Huttenlocher, 1979], it has been suggested that the inverted-U shaped developmental trajectory of gray matter volume seen in human MR scans is due to dendritic outgrowth and synaptogenesis, followed by synaptic pruning [e.g. Giedd et al., 1999]. An early paper by Giedd et al. [1999] showed this inverted-U shaped pattern of gray matter development across the frontal, temporal, and parietal cortical lobes, although not all subsequent studies have provided clear replication of this pattern (e.g. Shaw et al., 2008; Tamnes et al., 2009). In Giedd et al., the frontal and parietal lobes attained peak gray matter volume at age 11 in girls and 12 in boys, before undergoing an extended sequence of thinning into adulthood. The ages at which these peaks in gray matter volume were observed correspond to the sexually dimorphic ages of gonadarche onset, which suggests possible interactions between puberty hormones and grey matter development. Other MRI studies have shown the gradual emergence of sexual dimorphisms across puberty, with increases in amygdala volume during puberty in males only, and increases in hippocampus volume in females only [Lenroot et al., 2007; Neufang et al., 2009]. Thus, it is possible that neuroanatomical development in certain brain regions is more tightly linked to puberty than it is in other brain regions. However, no direct measures of puberty were acquired in these studies.

The Role of Puberty in Gray Matter Development

In recent years, a number of adolescent MRI studies have investigated in more detail the relationships among structural brain development, gender, and puberty. An adolescent structural MRI study by Peper et al. [2009b] showed evidence for a positive association between testosterone levels and global gray matter density in males (and not in females), while females showed a negative association between estradiol levels and both global and regional gray matter density. Whether these gender differences can be replicated, and whether they are indeed region-specific, remains to be seen. Elsewhere, evidence has been shown for region- and gender-specific effects of pubertal measures on structural brain measures. For example, Neufang et al. [2009] investigated relationships between gray matter volume, gender and pubertal measures in participants aged 8–15. The pubertal measures were physician-assessed Tanner stage and plasma concentrations of gonadotropic (LH, FSH) and gonadal (testosterone, estrogen) hormones. Irrespective of gender, there was a positive relationship between pubertal measures (Tanner stage and testosterone) and gray matter volume in the amygdala, and a negative relationship between these measures and hippocampal volume. In addition, there were gender-specific effects: females showed a positive relationship between estrogen levels and limbic gray matter, and males showed a negative relationship between testosterone and parietal cortex gray matter. All of these findings are preliminary and require replication, but they represent an important first step in this new area of research.

Adolescent White Matter Development

Many MRI studies show a steady linear increase in global white matter volume between childhood and adolescence, with this increase slowing and stabilizing into adulthood [Giedd et al., 1999; Tamnes et al., 2009]. This increase differs between the sexes across adolescence, with males showing considerably steeper age-related increases in white matter volume than do females [e.g. Perrin et al., 2008, 2009]. The increase in white matter volume has been attributed to progressive age-related axonal myelination observed in histological samples [Benes et al., 1994; Yakovlev and Lecours, 1967], or alternatively, to increasing axonal calibre [Paus et al., 2008].

In addition to changes in white matter volume, studies have shown concurrent changes in white matter microstructure. Fractional anisotropy (FA) is an MRI measure describing the extent to which the diffusion of water molecules in the brain is anisotropic (not equal in all directions). High FA values shown in diffusion tensor imaging (DTI)-MRI studies are thought to reflect increasing organization of white matter tracts, due to processes including myelination. Studies consistently show an increase in FA during adolescence, for example, in the frontal lobes [Barnea-Goraly et al., 2005]. To date, studies have not shown evidence for sexually dimorphic developmental trajectories of FA.

Another MRI measure that has been used developmentally is the myelin-transfer ratio [MTR: Perrin et al., 2008, 2009]. MTR provides information on the macromolecular content (e.g. myelin content) of white matter tissue. Unlike for FA, there is evidence for sexually-dimorphic developmental trajectories of MTR. Specifically, MTR has been shown to decrease with age across adolescence in males only [Perrin et al., 2008, 2009]. It has been suggested that this decrease in MTR reflects increasing axonal caliber, since the larger the caliber, the fewer axons will fit into the same unit of imaged volume and this will result in a relative decrease in the amount of myelin [Paus et al., 2008]. Questions remain regarding these intriguing findings using MTR: for example, whether these sex differences emerge prior to, or exclusively during, adolescence.

The Role of Puberty in White Matter Development

Developmental white matter trajectories differ as a function of pubertal measures. One study reported a positive relationship between LH concentration and white matter density at age nine; this relationship did not differ between the sexes [Peper et al., 2009a]. However, it has been shown that during adolescence, developmental trajectories of white matter volume, as well as the MTR, differ between the sexes. Recent studies by Perrin et al. [2008, 2009] have investigated whether this difference may be due to puberty hormones downstream from LH. Perrin et al. [2008] investigated the relationship between expression levels of a gene encoding the androgen (testosterone) receptor, and white matter development, in males. The results showed that variance in trajectories of white matter development in males was indeed related to gene expression levels, suggesting that effects of testosterone may be responsible for the sexually dimorphic relationship between age and white matter volume. In Perrin et al. [2009], evidence was presented for sexual dimorphism in the mechanism underlying adolescent increases in white matter volume.

In summary, a number of studies have shown evidence that gonadotropic and gonadal puberty hormones influence structural brain development. Further work is needed to investigate mechanisms underlying region-specificity and sexual dimorphism in the relationship between puberty hormones and brain development. Finally, studies thus far have not investigated possible interactions between the timing of pubertal events and structural brain development; this is an area for future investigation.

The Role Of Puberty In Cognitive Development

Only a small number of empirical behavioral studies have focused on the effect of puberty on a particular cognitive process. Some of the earliest studies focused on face processing. A study by Carey et al. [1980] showed that, while performance in a facial identity recognition task improved steadily during the first decade of life, this was followed by a decline in performance at approximately age 12. This decline may be due to puberty, rather than to age per se, as a later study showed that females at mid-puberty performed worse those at pre- or post puberty, when these groups were matched for age. More recently, evidence for a pubertal “dip” in facial emotion processing was shown [McGivern et al., 2002]. In this study, male and female participants aged 10–17 performed a match-to-sample task in which faces showing emotional expressions were matched with emotion words. An increase in reaction time of around 10–20% was shown at an age corresponding roughly to puberty onset (age 10–11 years in females, 11–12 in males), which then declined during adolescence to reach prepuberty levels at age 16–17. However, this study did not assess puberty stage. These results should now be replicated, for example with more accurate hormonal measures of puberty, and using longitudinally assessed cohorts. Further studies should also investigate whether these results are specific to face processing, or are a more domain-general effect of adolescent cognitive development.

The Effect of Sex Hormones on Cognitive Function

There is evidence that hormones can have different influences on behavior during puberty than in adulthood. For example, the challenge model of testosterone-aggression associations suggests that while testosterone levels increase during puberty, aggressive behavior does not show any simple relationship with testosterone during adolescence [Archer, 2006]. Rather, there is emerging evidence from both human and nonhuman primate studies that testosterone increases motivation to attain higher status, but the specific effects on behavior are dependent on the social and developmental context. It is important to emphasize the complexity of these issues-that is, we are at a very early point in integrating animal research (where experiments can be designed to elucidate specific hormonal effects on specific neural systems) and human studies, to address the important but complex issues regarding cognitive, emotional, and motivational changes directly linked to puberty [see Dahl and Gunnar, 2009, for further discussion of some of the clinical and public health implications].

However, there are a few areas of convergence emerging from research in this area that highlight promising areas of progress. For example, there is increasing evidence that adolescent changes in sensation-seeking may include some puberty-specific changes, and may provide new insights into adolescent risk taking. Sensation-seeking is one of the developmental contributors to risk behaviors and is more likely to emerge during adolescence than any other time period [e.g. Arnett and Balle-Jensen, 1993]. Sensation-seeking tendencies appear to be more strongly linked to puberty than to age [Spear, 2000]. One of the first studies to demonstrate the specific link between sensation-seeking and puberty focused on adolescents within the narrow age range of 11–14 years. Boys and girls with more advanced pubertal development had higher ratings of sensation seeking and greater drug use [Martin et al., 2002]. More recently, Steinberg and Monahan [2007] have found evidence that parsing sensation-seeking from the broader construct of impulsivity (which is sometimes experimentally confounded with sensation-seeking) shows an inverted U-shaped developmental trajectory, peaking at the time of pubertal maturation, and significantly linked to measures of puberty in boys. Dahl and Gunnar [2009, for further discussion] have reported a broader range of affective changes linked to puberty, for example emotions in response to social situations.

In summary, few studies as yet have investigated the link between puberty and cognitive development, and this area will be an interesting focus for future research.

The Role Of Puberty In Functional Brain Development As Measured By fMRI

A very small number of functional neuroimaging studies conducted thus far have included measures of puberty. However, a number of adult and adolescent functional MRI (fMRI) studies show gender differences in neural activity in a range of cognitive paradigms (a full review of these findings it is beyond the scope of this article). Some gender differences may be due to prenatal sex hormone effects, to puberty-independent effects of genes encoded on the sex chromosomes, or to gender-specific environmental effects across the lifetime. However, certain of these effects may be attributable to puberty. These effects could be mediated by effects on neural-to-hemodynamic coupling, via organizational or activational effects on neural responsiveness, influences on cognitive processing, or via indirect influences of pubertal transitions on cognitive processing via stereotypes and identity. Further studies are needed to elucidate these possible relationships.

Several fMRI studies have been conducted in populations with endocrine disruptions. Although the results are difficult to interpret with regards typical puberty and adolescence (these populations are hormonally abnormal prior to puberty onset), they provide converging evidence that determinants or correlates of puberty influence functional brain activity. For example, an fMRI study by Mueller et al. [2009] compared brain activity during a facial emotion-processing task between adolescent males with familial hyperandrogenism (causing excess testosterone from an early age). Relative to controls, the group with excess testosterone showed elevated hippocampal activity during fear processing, as well as faster behavioral responses to faces showing fearful expressions. In an fMRI study by Ernst et al. [2007], seven male and seven female adolescents with congenital adrenal hyperplasia (resulting in excess testosterone in utero) were compared with age- and gender-matched controls in a similar facial emotion-processing task. In contrast to the study by Mueller et al., no group differences were reported in the hippocampus. However, in the female clinical group, there was enhanced amygdala activity during fear and anger processing, relative to female controls. The enhanced amygdala activity in the female clinical group was similar to that in male controls, which suggests a mediating effect of testosterone.

Conclusion

Puberty represents a period of profound transition in terms of drives, emotions, motivations, psychology and social life. Recent preliminary evidence from developmental MRI studies has suggested that stage of puberty might play an important role in adolescent brain development, perhaps more so than chronological age. Further behavioral and neuroimaging studies are needed in which accurate and reliable measures of puberty are taken, to shed light on how puberty hormones influence the development of brain structure and function. Clearly, there is great value in achieving a better understanding of the relationships between the brain, cognition, behavior, and puberty. However, these goals will require conceptual and methodological advances focusing on how best to integrate different pubertal measures within developmental studies of adolescent brain and behavioral maturation.

Link to Article

Introduction.

Adolescence is a time of change, when children grow into adults. This period is marked by changes in the body, how the brain works, and how people interact with others. hese changes are influenced by hormones, which are chemicals that send messages throughout the body. Puberty is the time when these hormonal changes happen.

Puberty: The Beginning Of Adolescence

Puberty is a process that starts in early adolescence. It involves changes in the body as a result of three hormonal events: adrenarche, gonadarche, and activation of the growth axis. Gonadarche is often considered puberty. This process involves the release of hormones from the brain, which signal the body to start developing. These changes include the development of sexual characteristics, such as breasts in girls and facial hair in boys.

Hormonal Effects On Brain And Behavior

Hormones play a big role in how the brain develops and how people behave. Some of these effects happen early in life, but they can also continue into adolescence. These effects can change how people perceive things, how motivated they are, and how they behave. For example, hormones can make people more interested in romantic relationships.

Measuring Puberty In Studies Of Adolescent Brain Development

Scientists are trying to understand how puberty affects the brain. This is a tricky task because puberty is not a single event but a series of changes that happen over time. Scientists need to measure these changes carefully in order to understand their effects.

One common way to measure puberty is through a system called Tanner staging. This system looks at physical changes in the body, such as breast development in girls and genital development in boys. However, Tanner staging is not perfect and can be influenced by factors like weight.

Scientists can also measure hormones directly in blood or saliva, but this can be expensive and time consuming. It's also important to note that hormone levels can change throughout the day and month.

Puberty And Structural Brain Development As Measured By MRI

Scientists use MRI to look at the structure of the brain. MRI studies have shown that the brain continues to develop throughout adolescence, with changes in both gray matter and white matter. Gray matter is important for thinking and learning, while white matter helps different parts of the brain communicate with each other.

Studies show that both gray and white matter change in a predictable way as people get older, but these changes can also be influenced by puberty. For example, hormones can affect the growth of gray matter in certain parts of the brain, such as the amygdala, which is involved in emotions.

The Role Of Puberty In Cognitive Development

Puberty can affect how people think and learn. For example, some studies have shown that teenagers may experience a temporary decline in their ability to recognize faces during puberty. This could be due to hormonal changes in the brain.

The Role Of Puberty In Functional Brain Development As Measured By fMRI

fMRI is another imaging technique that can be used to study the brain. It allows scientists to see which parts of the brain are active during different tasks. Studies have shown that puberty can affect brain activity, especially in areas related to emotions.

Conclusion

Puberty is a crucial time for development. Hormones play a big role in how the brain and body change during this time. Scientists are continuing to learn about how puberty affects the brain and behavior, and these findings can help us understand the challenges and opportunities that teenagers face.

Link to Article

Introduction

Adolescence is the period of time when children transition into adults. During this time, teenagers experience major changes in their bodies, brains, and social lives. This time period is marked by the onset of puberty, a process of physical and hormonal changes that ultimately leads to sexual maturity. Puberty is a complex process that involves multiple hormone systems and has a significant impact on brain development and behavior.

Puberty: The Beginning Of Adolescence

Puberty is characterized by three major endocrine events: adrenarche, gonadarche, and the activation of the growth axis. Gonadarche is the most well-known aspect of puberty, and it refers to the activation of the hypothalamic-pituitary-gonadal (HPG) axis, which leads to the production of sex hormones and the development of reproductive capability. Adrenarche, or the activation of the hypothalamic-pituitary-adrenal (HPA) axis, occurs earlier than gonadarche and is characterized by the production of adrenal androgens. The third hormonal event, the activation of the growth axis, results in a growth spurt and changes in body size and composition.

Hormonal Effects On Brain And Behavior

The sex hormones estrogen and testosterone, as well as their weaker adrenal counterparts, have significant effects on the brain and behavior. These effects are believed to occur through two processes: organization and activation. Organizational effects occur during prenatal development and early childhood, when sex hormones permanently shape the brain's structure and function. Activational effects occur during puberty, when sex hormones act on established neural circuits to influence behavior. Puberty may trigger a second wave of brain reorganization and plasticity, with sex hormones influencing the development of brain structures involved in reproductive behavior, sensory processing, and reward seeking.

Measuring Puberty

Studying the effects of puberty on the brain requires careful consideration of how to measure pubertal maturation. The most commonly used measure of puberty is Tanner staging, a system that categorizes individuals along an ordinal scale based on physical characteristics such as pubic hair and breast development in females and pubic hair and genital development in males. While Tanner staging is considered the gold standard, it has limitations, including its reliance on visual assessments and its development on a relatively small sample of children. Hormone assays, which measure the levels of sex hormones in the body, are increasingly being used to measure pubertal stage, but they also have limitations, such as fluctuations in hormone levels and the lack of standardization in the use of different biological samples.

Puberty And Structural Brain Development As Measured By MRI

Magnetic resonance imaging (MRI) has revolutionized our understanding of brain development, allowing researchers to track changes in brain structure, including gray and white matter, throughout adolescence.

Adolescent Gray Matter Development

Gray matter, which contains the cell bodies of neurons, undergoes significant changes during childhood and adolescence. In many brain regions, gray matter volume follows an inverted-U shaped trajectory, initially increasing during childhood, reaching a peak during adolescence, and then declining steadily into adulthood. This pattern is thought to reflect dendritic outgrowth, synaptogenesis, and subsequent synaptic pruning.

The Role of Puberty in Gray Matter Development

Emerging evidence suggests that puberty hormones may play a role in gray matter development. Studies have shown associations between testosterone levels and gray matter density in males, and between estradiol levels and gray matter density in females. These associations may be region-specific, with different brain regions showing different patterns of development in response to puberty hormones.

Adolescent White Matter Development

White matter, which contains the axons that connect neurons, also undergoes significant changes during adolescence. MRI studies show a steady increase in white matter volume during this time, with the increase slowing and stabilizing into adulthood. This increase is thought to reflect myelination, the process by which axons are coated in a fatty substance called myelin.

The Role of Puberty in White Matter Development

Studies have shown that the development of white matter, particularly in terms of myelination, may be influenced by puberty hormones. For example, the expression levels of the androgen receptor have been linked to white matter development in males, suggesting that testosterone plays a role in the sexually dimorphic development of white matter during adolescence.

The Role Of Puberty In Cognitive Development

Puberty has been linked to changes in cognitive development, particularly in areas such as face processing and sensation-seeking.

The Effect of Sex Hormones on Cognitive Function

Sex hormones have complex effects on cognitive function, and these effects may vary depending on the developmental stage. For example, testosterone is associated with increased motivation to attain higher status, but its specific effects on behavior depend on the social and developmental context.

The Role Of Puberty In Functional Brain Development As Measured By fMRI

Functional magnetic resonance imaging (fMRI) studies have revealed gender differences in brain activity during a range of cognitive tasks. While some of these differences may be due to prenatal influences or genetic factors, others may be attributable to the effects of puberty.

Conclusion

Puberty is a critical period for brain development and behavior. Studies are beginning to unravel the complex interplay between puberty hormones and brain structure and function. Further research is needed to understand how these relationships influence cognitive development, sensation-seeking, and social behavior.

Link to Article

Introduction

Adolescence is the time when a person grows up from being a child to being an adult. This time is marked by big changes in the body, brain, and how a person interacts with the world. These changes start around the time puberty begins and involve hormones, physical growth, and how a person thinks and acts. Puberty is a time of big hormonal changes that make the body grow and develop. The end of adolescence happens when a person has taken on a grown-up role in life, like a job or starting a family.

Scientists are still learning about how puberty affects the brain, but studies on animals show that hormones during puberty have a big impact on how the brain works and how a person behaves. In recent years, more studies on humans are showing that puberty might be important for how the brain develops.

Puberty: The Beginning Of Adolescence

Early adolescence is when a person goes through puberty, a time when their body goes through a lot of changes. Puberty involves three main changes in hormones:

1. Adrenarche: This happens first, starting around ages 6 to 9 in girls and a year later in boys. It involves changes in hormones from the adrenal glands, which are small glands near the kidneys. These hormones make body hair grow and cause changes in sweat glands.

2. Gonadarche: This is what people usually think of as puberty. It starts with the brain telling the ovaries (girls) or testes (boys) to start working properly. This happens around ages 8 to 14 in girls and 9 to 15 in boys. The ovaries and testes make the hormones estrogen (girls) and testosterone (boys), which cause the body to develop in ways that make a person able to have children.

3. Growth Axis Activation: This involves a big growth spurt in height and changes in body size and shape. This happens around age 12 for girls and 14 for boys.

Hormonal Effects On Brain And Behavior

Puberty hormones not only change the body but also affect the brain and how a person acts. These effects are often thought to happen in two ways:

1. Organization: These effects happen before birth and in early childhood. Hormones during these times help to shape the brain in ways that make it "male" or "female."

2. Activation: These effects happen during puberty and make the brain respond to hormones in ways that prepare a person for adult life and for having children.

Scientists think that puberty also causes a second wave of brain changes that make the brain more flexible and able to learn new things. While animal studies show these changes, we're still learning about how puberty changes the brain in humans.

Measuring Puberty

Scientists who study adolescent brains need to carefully measure puberty to understand how it affects brain development.

Puberty isn't just one thing, but a series of changes that happen over several years. Scientists need to measure these changes accurately to see how they link to changes in the brain.

One common way to measure puberty is through the Tanner stages, which look at physical signs like body hair growth, breast development (girls), or genital development (boys). While these stages are helpful, they are not perfect. There are some problems with them, like the fact that they were developed using a small group of people and might not work the same way for everyone.

Another way to measure puberty is by testing hormone levels in blood, saliva, or urine. This can be very helpful, but it can also be expensive and time-consuming. Also, hormone levels change a lot throughout the day and month.

Scientists also use self-reported measures of puberty, like questionnaires, but these are not always accurate.

Puberty And Structural Brain Development As Measured By MRI

Scientists use special imaging techniques like MRI to see what the brain looks like and how it changes. MRI shows us things like:

• Gray matter: This is where most of the brain's cells are. Gray matter changes a lot during adolescence, with more growing and then shrinking as the brain gets more efficient. Scientists think that puberty might be important for how gray matter changes.

• White matter: This is like the brain's "wires," connecting different parts of the brain. White matter keeps growing during adolescence, but boys' white matter grows faster than girls'. Scientists think that this difference might be related to puberty hormones.

The Role Of Puberty In Cognitive Development

While we're still learning about how puberty affects cognition (thinking, memory, and learning), some early studies show that puberty might be linked to changes in how people process faces and emotions.

• Face processing: Some studies show that people get worse at recognizing faces around the time of puberty.

• Emotion processing: Some studies suggest that people might have a harder time recognizing emotions on faces during puberty.

Scientists are now trying to see if puberty affects other kinds of thinking and learning, and if these changes are tied to specific hormones.

The Role Of Puberty In Functional Brain Development As Measured By fMRI

fMRI is another type of brain imaging that shows how different parts of the brain work. While few fMRI studies have looked at puberty, those that have show that puberty might play a role in how different parts of the brain respond to tasks.

Conclusion

Puberty is a big deal for the brain and how a person acts. Scientists are learning more about the link between puberty and brain development. Future studies are needed to understand this link better. This knowledge will help us understand the brain and behavior of adolescents and how to help them during this important time of life.

Link to Article

Introduction

Puberty is a time when our bodies grow and change a lot. It's like a bridge between being a kid and being a grown-up. When we go through puberty, our bodies make lots of new hormones, which are like messages that tell our bodies how to grow and change. Puberty also makes our brains change and grow, and these changes can affect how we think, feel, and act.

Puberty: The Beginning Of Adolescence

Puberty is the time when our bodies start to become able to have babies. It starts when a part of our brain called the hypothalamus sends a message to another part of our brain called the pituitary gland. The pituitary gland then sends a message to our ovaries (girls) or testes (boys). This message tells them to start making eggs (girls) or sperm (boys).

Hormonal Effects On Brain And Behavior

The hormones our bodies make during puberty affect our brains and how we behave. Hormones like estrogen and testosterone can make our bodies grow, and they can also affect our brains. These hormones can also change how we feel about things. For example, they can make us feel more attracted to other people.

Measuring Puberty In Studies Of Adolescent Brain Development

It's hard to study how puberty affects our brains because puberty is a long process, not just one event. Scientists need to figure out the best ways to measure puberty so they can study how it affects our brains. One way to measure puberty is to look at how developed our bodies are. Another way is to measure the amount of hormones in our blood.

Puberty And Structural Brain Development As Measured By MRI

MRI is like a special camera that can take pictures of our brains. Scientists use MRI to see how our brains change as we grow up. MRI shows that our brains keep growing and changing even after puberty. It also shows that different parts of our brains grow at different times. Scientists are trying to figure out if puberty hormones might affect how our brains grow.

The Role Of Puberty In Cognitive Development

Puberty can affect how we think and learn. For example, puberty might affect how well we can remember things. Scientists are still learning about how puberty affects our brains and how we learn.

The Role Of Puberty In Functional Brain Development As Measured By fMRI

fMRI is another kind of special camera that can show how our brains work. Scientists are using fMRI to see how puberty might affect how different parts of our brains work together. It's a new area of research, and scientists are still learning a lot.

Conclusion

Puberty is a very important time. It's a time when our bodies, brains, and minds change a lot. It can be confusing and exciting, all at the same time. Scientists are still learning about how puberty affects us, but we know that it is a time of growth and change.

Link to Article