In 2010, a sixteen-year-old boy named Kalief Browder was arrested in New York City for allegedly stealing a backpack. Unable to afford bail, he was sent to Rikers Island where he spent almost two years in solitary confinement. During that time, he became floridly psychotic. Browder maintained his innocence throughout his incarceration, and in 2013 the charges against him were dropped. But the damage was done. Though he completed his GED and started college, he continued to struggle with paranoia and depression, requiring multiple hospitalizations. In June 2015, he died by suicide.

Unfortunately, stories like Browder’s are appallingly common. Almost 2 million people are behind bars in the United States – of those, more than 20% have not been convicted of any crime. Approximately 1 in 5 inmates has spent time in solitary confinement within the past year, including a disproportionately high percentage of Black individuals (above and beyond the already disproportionately high rate of detainment). Symptoms of “serious psychological distress” occur in approximately 25% of individuals (a term used to connote severe psychiatric illness). The practice is rampant: how can we understand its biological impact??

200 years ago, Charles Bonnet, a naturalist and philosopher, was studying entomology and botany when something personal caught his attention. Bonnet’s grandfather was losing his vision due to bilateral cataracts and began to experience hallucinations of people, animals, and even buildings. Bonnet became the first to describe this phenomenon and, in a stroke of insight, postulated that the hallucinations originated from the visual cortex rather than the eyes themselves.

Bonnet’s work echoed earlier discoveries. Ambroise Pare, a “barber” in the 1500s, described the peculiar experience of a man complaining of leg pain – peculiar because the leg had been amputated months prior (a phenomenon later termed “phantom limb pain”). Multiple physicians, including the famed neurologist, Oliver Sacks, described musical hallucinations emerging in elderly adults experiencing hearing loss. Common to these stories was the idea that losing sensory input could cause perceptual disturbances within the same domain.

Of course, establishing causation requires more than retrospective accounts. Enter Donald Hebb, already famous for his foundational work on synaptic plasticity. Hebb was studying the impact of boredom (!) when he designed what seemed like a simple enough experiment. He recruited college students and placed them into small cubicles. He blocked their vision with goggles, played a low frequency hum to suppress outside sound, and prevented tactile input by placing their arms and legs within tubes. Hebb expected that subjects would remain in this space for weeks. Not a single subject lasted more than seven days. Some experienced intense delusions, others cognitive impairment, some frank hallucinations. The effect was so profound that it became part of the CIA’s MK Ultra Project and was ultimately incorporated into “enhanced interrogation” practices. It was clear that depriving people of sensory and social input could induce psychotic symptoms. But it wasn’t clear how.

One early insight came from a model known as signal detection theory. The basic idea is that the brain is never silent – even at rest, neurons fire intermittently. A task of the cortex, at any moment, is to determine whether a signal from the periphery reflects a novel stimulus or is just random firing. Critically, in the absence of external input, the brain may lower its threshold for what it interprets as a stimulus and be more likely to misinterpret background noise as “real."

More recently, the predictive coding model builds on this using a Bayesian approach: the task of the cortex is not just to receive sensory data, but to interpret them based on prior probabilities. Thus, even if an incoming signal is low (or absent), a person may still have a perceptual experience – a hallucination – if they have strong prior expectations. For example, if subjects are repeatedly presented with a paired light and soft sound, they will be more likely to report hearing the sound when they see a light. This phenomenon has been reliably shown in numerous experiments across sensory modalities.

Signal detection and Bayesian theories offer a compelling model for how sensory deprivation could lead to hallucinatory experiences. But what about more complex neurobiological systems, like those responsible for social perception and behavior?

Harry Harlow was studying rhesus macaques at his lab in Madison, Wisconsin when an outbreak of tuberculosis precipitated an unexpected discovery. To prevent the spread of disease, Harlow was forced to separate infant monkeys from their mothers. In the aftermath, he observed a curious behavior: when someone tried to take away an infant’s dirty diaper, they would become upset and cling to it. Harlow took this to mean that they craved physical contact. The observation prompted what became one of the most famous experiments in the history of psychology, in which he showed that infant monkeys preferred an inanimate monkey covered in soft cloth to a wire monkey with a bottle of milk. The need for physical contact seemed even greater than the need for food. But this was only a small part of what happened.

Rarely discussed was that all of the infant monkeys showed significant long-term harm. They lacked basic social skills, sexual behavior with peers was absent, and when the females did get pregnant, they abused their young. While they preferred a soft monkey to a wire monkey, what they needed was an actual mother.

But Harlow wasn’t done. He became fixated on the impact of early social relationships. In the wire monkey study, the animals had contact with the experimenters and indirect contact with other animals. To more rigorously test his ideas, he created what he called total social isolation. He raised infant monkeys in a cage surrounded by steel walls, with no outside contact. Then, after up to a year, he released them back into a space with other animals. The results were devastating. The monkeys emerged in a “state of emotional shock.” Some refused to eat and died from starvation. The autopsy identified the cause of death as “emotional anorexia." Harlow’s work, along with notable others’, formed the foundation of what we now call attachment.

Decades later, another researcher, Ralph Hoffman, became fascinated by peoples’ social relationships and their connection to psychosis. Clinical dogma at the time was that social deficits were a consequence of schizophrenia. But Hoffman was struck by data that social isolation frequently preceded the first experience of a hallucination. In the same way that sensory deprivation could cause auditory and visual disturbances, Hoffman wondered whether the absence of social input could cause hallucinations or delusions with “compelling, aberrant social meaning.” He spent years studying this and ultimately brought these ideas together into the Social Deafferentation Hypothesis.

Tragically, Hoffman died before he could test the model. Nevertheless, the relationship between loneliness and the incidence of hallucinations has been demonstrated multiple times since, including one recent study that showed a specific increase in hallucinations with social meaning. Others have documented additional pathways through which social isolation can cause profound neurobiological harm.

This begs the question: if the absence of social stimulation can lead to psychosis, can enhancing social connectivity help to treat psychosis?

Early data are promising. A 2012 meta-analysis of 19 studies found evidence of benefit for social cognitive training in people with schizophrenia. A more recent study found improved global function over antipsychotic medication alone when individuals with schizophrenia had their social support bolstered through participation in a community club.

Yet somehow, social interventions do not resonate with clinicians or the public as being “real” in the same way as clozapine or ECT. This is despite the fact that psychosocial interventions like family psychoeducation, supportive employment, and supportive housing often show larger effect sizes than medications.

These findings force us to reconsider the false dichotomy of biologic vs psychosocial factors. Social isolation is a biological insult. And social treatments are biological treatments.

It is hard to confront the truth of Kalief Browder’s story: that an innocent child was imprisoned, subjected to what many would consider torture, and died soon after. The work of Hebb, Harlow, and Hoffman offer a stark perspective: whether we attribute Browder’s death to “emotional anorexia” or “psychosis” or “depression” the cause is the same. We now know that social isolation can cause irreparable biological harm.

And still: hundreds of thousands of Americans are subjected to this each year. Many of these are individuals who have never been convicted of a crime; many are adolescents, in the age of maximum vulnerability to developing psychosis; many are people with severe mental illness who, due to the history of transinstitutionalization, have de facto had their care relegated to the carceral system.

Researchers often focus on the importance of translating their work from basic science into clinical settings. Sometimes, the need is more acute: to reach beyond the bedside, to engage in broader public dialogue, and to advocate for social justice.

Summary

The case of Kalief Browder, a teenager arrested in New York City in 2010 for alleged backpack theft, illustrates the severe consequences of extended incarceration and solitary confinement. Unable to afford bail, Browder spent nearly two years in solitary on Rikers Island, during which time he developed severe psychological distress, including psychosis. Despite the charges being dropped in 2013, he continued to experience paranoia and depression, ultimately dying by suicide in 2015. Such experiences are unfortunately common, with nearly 2 million individuals incarcerated in the United States, over 20% of whom await conviction. A significant proportion, approximately one in five, has endured solitary confinement within the past year, with a disproportionately high representation of Black individuals. This practice is linked to severe psychiatric illness, affecting about 25% of individuals experiencing "serious psychological distress."

Historical observations and experimental research have shed light on the neurobiological impact of deprivation. Charles Bonnet's 18th-century description of visual hallucinations in his vision-impaired grandfather, along with earlier accounts of phantom limb pain and musical hallucinations in individuals with hearing loss, suggested that a loss of sensory input could induce perceptual disturbances. This concept was rigorously tested by Donald Hebb in the mid-20th century. Hebb's sensory deprivation experiments, which isolated college students from all external stimuli, demonstrated that a lack of sensory and social input could induce profound psychological effects, including delusions, cognitive impairment, and hallucinations. These findings were so impactful they were later incorporated into "enhanced interrogation" practices. Mechanisms explaining these effects include signal detection theory, where the brain lowers its threshold for interpreting internal noise as external stimuli in the absence of input, and predictive coding models, where strong prior expectations can lead to perceptual experiences even without incoming sensory data.

The impact of social deprivation on psychological well-being has also been extensively studied. Harry Harlow's seminal research on rhesus macaques in the mid-20th century revealed the critical need for physical and social contact, showing that infant monkeys preferred a cloth surrogate mother over a wire mother providing food. Crucially, all socially deprived infant monkeys exhibited significant long-term harm, including impaired social skills, absence of sexual behavior, and abusive parenting. Harlow's "total social isolation" experiments, where infant monkeys were raised without any contact, resulted in severe emotional shock, refusal to eat, and even death from "emotional anorexia." This body of work formed the foundation of attachment theory. Later, Ralph Hoffman proposed the Social Deafferentation Hypothesis, suggesting that chronic social isolation could similarly cause hallucinations or delusions with social meaning, much like sensory deprivation causes perceptual disturbances. Subsequent research has consistently supported the link between loneliness and the incidence of hallucinations.

These insights into the neurobiological effects of isolation have important implications for the treatment of psychosis. Early evidence suggests that social interventions, such as social cognitive training and community-based social support, can improve global function in individuals with schizophrenia, sometimes more effectively than antipsychotic medication alone. Despite these promising results and the observation that psychosocial interventions often yield larger effect sizes than pharmacological treatments, they frequently receive less recognition from clinicians and the public. This disparity highlights a false dichotomy between biological and psychosocial factors, as social isolation represents a profound biological insult, and social treatments are, in essence, biological treatments that impact brain function and well-being.

The tragic story of Kalief Browder underscores a critical societal issue. The research by Hebb, Harlow, and Hoffman provides a stark reminder that severe social isolation can inflict irreparable biological harm. Hundreds of thousands of individuals in the United States, including many who have not been convicted of a crime, adolescents in vulnerable developmental stages, and those with severe mental illness, are subjected to such conditions annually within the carceral system. Addressing this issue requires more than translating basic science into clinical practice; it demands a broader public dialogue and advocacy for social justice to prevent further harm.

Summary

In 2010, a sixteen-year-old named Kalief Browder was arrested in New York City, accused of stealing a backpack. Because his family could not afford bail, he was sent to Rikers Island. He spent nearly two years there in solitary confinement, during which time he developed severe mental health issues. Browder maintained his innocence, and the charges against him were eventually dropped in 2013. Despite earning his GED and starting college, he continued to struggle with paranoia and depression, requiring multiple hospitalizations. He died by suicide in June 2015. Sadly, cases like Browder's are not rare. Approximately 2 million people are incarcerated in the United States, with over 20% not yet convicted of any crime. Around one in five inmates has experienced solitary confinement in the past year, with a disproportionately high number of Black individuals affected. Many of these individuals, about 25%, experience severe psychological distress. The widespread use of solitary confinement raises serious questions about its biological impact on individuals.

The understanding of how sensory deprivation affects the mind has a long history. Two hundred years ago, naturalist Charles Bonnet observed his grandfather, who was losing his vision, begin to hallucinate people, animals, and buildings. Bonnet was the first to document this phenomenon, known as Charles Bonnet Syndrome, and correctly suggested that these hallucinations came from the visual cortex, not the eyes. Earlier observations, such as Ambroise Pare's description of "phantom limb pain" in the 1500s and Oliver Sacks' accounts of musical hallucinations in adults with hearing loss, also highlighted how the loss of sensory input could lead to perceptual disturbances. To establish a clearer cause-and-effect relationship, psychologist Donald Hebb conducted an experiment. He placed college students in cubicles, blocking their vision and hearing and limiting their sense of touch. Hebb expected them to tolerate this for weeks, but none lasted more than seven days. Subjects experienced intense delusions, cognitive impairment, and hallucinations. This profound effect demonstrated that depriving individuals of sensory and social input could induce psychotic symptoms, raising questions about the underlying mechanisms. Early explanations included signal detection theory, which suggests the brain may lower its threshold for interpreting background noise as real when external input is absent. More recent predictive coding models build on this, proposing that the brain interprets sensory data based on prior expectations, potentially leading to hallucinations even with minimal external signals.

Beyond sensory input, social interaction plays a critical role in neurobiological systems. Harry Harlow's research with rhesus macaques in the mid-20th century provided groundbreaking insights. When infant monkeys were separated from their mothers due to a tuberculosis outbreak, Harlow observed they craved physical contact, even clinging to dirty diapers. His famous experiment showed that infant monkeys preferred a soft, cloth "mother" over a wire "mother" that provided milk, suggesting that the need for physical comfort was greater than the need for food. However, all the isolated infant monkeys suffered long-term harm, exhibiting poor social skills, a lack of sexual behavior, and, if they became mothers, abusing their own young. This highlighted that while physical contact was important, an actual mother was essential for healthy development. Harlow's subsequent experiments on "total social isolation," where infant monkeys were raised without any contact, produced devastating results. Monkeys released after a year displayed "emotional shock," some refusing to eat and dying from what was termed "emotional anorexia." This work significantly contributed to the understanding of attachment theory. Decades later, researcher Ralph Hoffman explored the link between social relationships and psychosis. While clinical thinking at the time suggested social deficits were a result of schizophrenia, Hoffman noted that social isolation often preceded the first psychotic episode. He proposed the Social Deafferentation Hypothesis, suggesting that the absence of social input could directly cause hallucinations or delusions with social meaning, similar to how sensory deprivation causes visual or auditory disturbances. Though Hoffman died before fully testing his model, subsequent studies have repeatedly demonstrated a link between loneliness and the incidence of hallucinations, particularly those with social content, and confirmed other neurobiological harms caused by social isolation.

Given that a lack of social stimulation can lead to psychosis, a critical question emerges: can enhancing social connectivity help treat psychosis? Early findings show promise. A 2012 meta-analysis of nineteen studies indicated benefits for social cognitive training in individuals with schizophrenia. A more recent study demonstrated that individuals with schizophrenia who received bolstered social support through community club participation experienced improved global function, outperforming those receiving antipsychotic medication alone. Despite these positive results, social interventions often do not receive the same recognition or perceived legitimacy from clinicians or the public as pharmacological treatments or procedures like ECT. This perception persists even though psychosocial interventions—such as family psychoeducation, supportive employment, and supportive housing—frequently demonstrate larger positive effects than medications. These findings compel a reevaluation of the artificial separation between biological and psychosocial factors. The evidence suggests that social isolation acts as a biological insult, and, conversely, social treatments function as biological treatments, influencing brain chemistry and function.

It is difficult to fully grasp the truth of Kalief Browder’s story: an innocent adolescent imprisoned, subjected to conditions many would consider torture, and whose life ended soon after his release. The research of Hebb, Harlow, and Hoffman provides a stark perspective, showing that whether one attributes Browder’s death to "emotional anorexia," "psychosis," or "depression," the underlying cause is consistent: social isolation can inflict irreparable biological harm. Disturbingly, hundreds of thousands of Americans endure such conditions each year. Many of these individuals have never been convicted of a crime. Many are adolescents, a period of maximum vulnerability for the development of psychosis. And many are people with severe mental illness whose care has been effectively relegated to the carceral system due to a history of institutional neglect. Researchers often emphasize translating their work from basic science into clinical practice. However, sometimes the need is more urgent: to extend understanding beyond the healthcare setting, engage in broader public dialogue, and advocate for social justice.

Summary

In 2010, a 16-year-old named Kalief Browder was arrested in New York City for allegedly stealing a backpack. Because his family could not afford bail, he was sent to Rikers Island, where he spent nearly two years in solitary confinement. During this time, his mental health severely declined. Though charges were dropped and he attempted to move forward, he continued to struggle with paranoia and depression, eventually dying by suicide in 2015. Sadly, stories like Browder's are common. Of the almost 2 million people in jail or prison in the United States, more than 20% have not been convicted of a crime. Approximately one in five inmates has spent time in solitary confinement recently, including a high number of Black individuals. Many experience severe mental distress, highlighting the urgent need to understand the biological effects of such practices.

Over 200 years ago, Charles Bonnet described how his grandfather, losing his vision, began to see people, animals, and buildings that were not there. Bonnet suggested these visions came from the brain's visual center, not the eyes. Other observations supported this idea: a man with an amputated leg still felt pain in it (phantom limb pain), and elderly adults with hearing loss experienced musical hallucinations. These stories shared a common theme: losing sensory input could cause the brain to create perceptions in that same sensory area. Psychologist Donald Hebb further demonstrated this with an experiment where college students, deprived of sight, sound, and touch, developed delusions and hallucinations within days. This showed that severe sensory deprivation could indeed induce psychotic symptoms.

Scientists have since developed models to explain how the brain reacts to a lack of input. One idea, called signal detection theory, suggests that the brain is always active. When there's no external information, the brain might lower its guard and misinterpret its own background activity as real signals. Another model, predictive coding, suggests the brain uses past experiences to predict and interpret sensory data. If someone strongly expects to experience something, their brain might create that perception even if there's no actual input, like hearing a sound when seeing a light they've been taught to associate. These theories offer strong explanations for how sensory deprivation can lead to hallucinations.

Building on the understanding of sensory deprivation, researchers also explored the impact of social isolation. Harry Harlow's famous experiments with rhesus monkeys showed that infant monkeys deeply needed physical contact, preferring a soft, cloth "mother" over a wire one that provided food. Importantly, all the isolated monkeys suffered severe long-term harm, lacking basic social skills and abusing their own offspring. Harlow's most extreme experiment involved raising infant monkeys in total social isolation, leading to emotional shock, starvation, and even death from "emotional anorexia." This work formed the basis of attachment theory. Later, researcher Ralph Hoffman proposed that social isolation, like sensory deprivation, could cause "socially meaningful" hallucinations or delusions, a concept he called the Social Deafferentation Hypothesis. Research has since confirmed the link between loneliness and the occurrence of hallucinations.

These findings raise a crucial question: if a lack of social connection can cause psychosis, can improving social connectivity help treat it? Early research suggests yes. Studies have shown benefits from social cognitive training and community support groups for individuals with schizophrenia, sometimes even outperforming medication alone in improving overall functioning. Despite strong evidence, social interventions are often not seen as "real" treatments in the same way as medications or other medical procedures. This ignores the fact that social isolation causes significant biological harm, meaning social treatments are also, in effect, biological treatments. Kalief Browder's tragic story highlights this truth: his suffering and death were a direct result of the profound, irreparable biological damage caused by social isolation. Hundreds of thousands of Americans, including many who have not been convicted of crimes, adolescents, and those with severe mental illness, continue to be subjected to similar conditions each year. Therefore, addressing this issue requires not just clinical efforts, but also broader public discussion and advocacy for social justice.

Summary

In 2010, a teenage boy named Kalief Browder was arrested. He was sent to Rikers Island because his family could not pay for his release. He spent nearly two years there, much of it alone in a small room. During that time, he became very mentally ill. The police dropped the charges against him in 2013, but the harm was done. He continued to struggle with sadness and fear, needing to go to the hospital many times. In 2015, he died by suicide. Sadly, stories like Kalief's are common. Many people in jail have not been found guilty of a crime, and many spend time alone in small rooms. This practice often leads to serious mental health problems.

Over 200 years ago, a scientist named Charles Bonnet noticed that his grandfather, who was losing his eyesight, began to see things that were not there. Bonnet thought these visions came from the brain, not the eyes. Other doctors also saw similar things. For example, a person whose leg was cut off still felt pain in that leg, and older people losing their hearing started hearing music. These stories showed that when a person loses input from their senses, the brain can create its own experiences. Later, a scientist named Donald Hebb kept students in quiet rooms with no sights, sounds, or touch. They quickly began to see and hear things that were not real, and their minds became confused.

How does this happen? The brain is always a bit busy. When there are no outside messages, the brain might think its own small signals are real things. Also, the brain uses past experiences to guess what it "sees" or "hears." If it strongly expects something, it might "see" or "hear" it even if it's not truly there. This means that when a person is kept from seeing, hearing, or touching things, their brain can start making up its own reality, leading to seeing or hearing things that are not real.

Another scientist, Harry Harlow, studied baby monkeys. He found that baby monkeys needed touch and comfort more than food. When they were kept away from their mothers, even if they had food, they grew up unable to act normally with other monkeys. They often hurt their own babies later in life. Harlow even raised some baby monkeys completely alone in cages. Many of these monkeys became very sick, and some died from sadness because they had no contact with others. This work showed how important early social contact is for proper development.

Later, a researcher named Ralph Hoffman wondered if being lonely could also make people very sick in the mind, causing them to see or hear things that weren't real. Studies have since shown that being alone can indeed harm the brain deeply. Yet, social help like joining community groups is often not seen as truly treating mental illness, even though it can work better than medicines. It is important to know that being alone deeply hurts a person's body and mind. Kalief Browder's sad story shows that being held apart from others caused him great harm. Many people are still kept alone in jails today, including young people and those with serious mental illness. It is important to speak up and work for a fairer system that understands the deep harm caused by social isolation.