Heavy-set, with a soft-jowled face, King has a distinctly ursine air about him. We first meet at a Wendy’s in downtown Brooklyn, his teddy-bearishness rounded out by a plushy layer of cocoa-coloured velour tracksuit with a matching hoodie, T-shirt, and beanie hat. He is a garrulous, flirty raconteur. He leans in close over the small white plastic table in the corner and shares, in a gravelly voice, his penchant for Dominican women (‘I’ll take one as my next wife’), his distaste for Indian shop-owners (‘They look at you like you in a zoo. Or the bottom of they shoe’), and his love for his two-year-old grandbaby Vanny. But when he talks about his three-decade long ‘bid’ in various upstate correctional facilities, punctuated by periods of isolation in ‘the Box’ – a solitary confinement cell – he gets quieter, and stares away, distracted and angry.

‘I was in the Box a number of times,’ he says, ‘for dirty urine – when they find weed in your urine – and for arguing with the police over dumb shit. I was never there for stabbin’ or nothin’.’ He produces a long, thin Chick-O-Stick from his pocket and begins to chew on the bright orange flesh. ‘I seen some people, they go into the Box with 30 days, and they in that motherfucker for three years because they went off on a police officer; took some shit or piss and slung it on ’em because they had nothin’ better to do. Once they been there a minute, that’s when they start to see shit, harm themselves, harm others. I wasn’t in there banging my head on the wall, screaming and carrying on. I was chillin’, readin’, I ain’t bother no people.’

In the summer of 2007, King spent 75 days in the Special Housing Unit (SHU) of Fishkill Correctional Facility, a 19th-century asylum-turned-prison in Dutchess County in upstate New York. ‘Some rat told a correctional officer I was selling weed,’ he recalls. ‘So they gave me a Tier 3 ticket [a disciplinary hearing for violating prison rules], and 75 days in the Box.’ He found himself inside a 7ft x 10ft concrete cell with a small bed and toilet. It had a solid metal door with a small window made of hard plastic, out of which he could see a catwalk. A few times a day he saw correctional officers walking past, and once a day, a nurse dispensing medication.

Every morning, for an hour’s recreation, a door at the back opened out on to a ‘recreation cage’: a slightly bigger Box with a tiny, barred window. King wasn’t enamoured of the view: ‘A highway, some grass and trees, and sea gulls flyin’, shittin’ all over the place, eatin’ garbage that other inmates threw out.’ He had been in the Box a couple of times before, but these 75 days were the longest he’d ever been stuck there. After a few days, he found himself double-bunked – penned in with another inmate.

Nobody liked being double-bunked. It felt like being in a cash-strapped zoo, caged in with a restive animal that might turn on you unprovoked. ‘You could get beat up by your bunkmate, or by the police,’ says King. ‘Anything can happen. You ain’t got no wins in there.’

King’s first cellmate was a young Blood (affiliated with the street-gang founded in Rikers Island prison in 1993), who tried to intimidate him and order him around. Then came an ‘ugly-ass motherfucker’ whom King could barely resist throttling after he caught him ‘sneak-thieving’ – rifling his bag for stamps, jealously hoarded prison-currency, in the dead of night. King had no visitors, no classes, no yard-time smoking weed with his friends. The hours stretched on, with a corroding undertow of tension. It was like hanging around in a kennel-sized doctor’s waiting room for an appointment that never came. Worse, he was deprived of the small income he made outside from dealing marijuana and salami smuggled from the kosher kitchen, and his twice-weekly treat of cigarettes, condiments and canned fish from the commissary. All he had was Box food – ‘nasty chicken-soup slop’ – and the relentless, maddening soundtrack of ‘people buggin’ out’.

‘All day, every day in the Box,’ he recalls, staring down at the table, ‘people go off. They yell, they scream, they talk to they-self. They cuss the police out, call them all types of names: “Cracker!” “Incest baby!” At two or three in the morning, somebody starts screaming “Aaaaaa!” You don’t do nothin’, you shake your head sayin’, “Another one”.’

He longed for some communication from the outside world. Every day, during his first month, he wrote increasingly torrid letters to a young woman named Mercedes, whom he addressed as Babygirl. ‘She lived in New York,’ he says. ‘She worked in the corporate world, in one of those big-ass buildings downtown.’ He was pleased to receive her replies several times a week, even though he had to write them himself. ‘I sent them out without a stamp so they’d come back,’ he says. ‘It was make-believe. To have something to do.’

King has been out of prison for four years. But he’s travelling within a lonely Box wherever he goes. ‘I still don’t meet people. I’m alone,’ he says. ‘I got my back to the door when I take the train. I can’t have anyone behind me. I hate being in crowds. That’s why in four years I ain’t gone to see that ball drop [in Times Square on New Year’s Eve]. Fuck that ball! I see that shit on TV.’

He struggles with paranoid fears – of being cut in the face by an assailant, of a policeman spotting him and deciding, for some occult reason, to beat him up. The first year of his release, he went on antidepressants – ‘the doctors said I was mentally unstable.’ He’s since gone off them because they had an irksome diuretic sideeffect.

King says he hates talking about his time in the Box. ‘I don’t want to think about that shit and go back there, when things were critical,’ he says, his voice rising. ‘I didn’t have an all-right bid. It’s hard to talk about. The last thing I want to talk about. You want to wipe that shit from your memory.’

But the shit that went down in the Box happens to be the most indelible kind of shit there is. The sound of a metal door sliding shut – a high-pitched whirring that ends in a kh-khaat! of existential finality – reverberates in the ear years after leaving prison. The perpetual hyper-adrenalised wait for unknown adversaries. The feeling of being so alone that everything and everybody becomes distant and unreal. The unrelieved boredom that thickens into frustration, then anger, then fear and rage. The unabating dread and apprehension that pens you in your bedroom day after day. The horrors of the Box grow out of ordinary-seeming experiences: stress, boredom, tension. In the absence of family or friends or someone to call Babygirl, these pressures intensify and wear down one’s increasingly precarious sanity.

In 2005, there were an estimated 81,600 prisoners in solitary in the US; this month’s Senate Subcommittee Hearing puts the numbers at about the same. That’s 3.6 per cent of the 2.2 million presently incarcerated, many of whom, like King, were put in there for random acts of non-violent rule-breaking. Some, like him, shuttle in and out of solitary; others remain locked up for decades. Prison authorities in every state are running a massive uncontrolled experiment on all of them. And every day, the products of these trials trickle out on to the streets, with their prospects of rehabilitation professionally, socially, even physiologically diminished. The Box, as psychologists and psychiatrists have been saying for decades, damages the mind. But evidence from neuroscience increasingly suggests that it is irrevocably harming the brain, too.

In the fall of 1982, the forensic psychiatrist Stuart Grassian visited Walpole State Penitentiary, Massachusetts’s only maximum-security prison at the time. He went there at the behest of a legal aid attorney, who wanted him to evaluate the mental health of the inmates in the prison’s segregation unit. He spoke to 14 young men who’d been in isolation for several months, each in a 6ft x 9ft cell with a barred inside gate, and a steel door with a voice box and a dirt-stippled glass panel the width of his face. Grassian expected to hear fantastically exaggerated claims from prisoners looking to dupe their way out of the unit, but each vociferously denied that anything was the matter. ‘Solitary doesn’t bother me,’ one told him. ‘Some of the guys can’t take it, I can,’ said another. With close questioning, Grassian wrote later in the American Journal of Psychiatry, the second prisoner ‘came to describe panic, fears of suffocation, and paranoid distortions while he had been in isolation’, while the first had recently slashed his wrists because he ‘figured it was the only way to get out of here’.

They suffered a range of symptoms: stupor, delirium, hallucination, and a loss of ‘perceptual constancy’ – the ability to recognise the sameness of things when viewed from different distances and angles. Many had painfully sharpened senses. One lived in dread of prisoners on the tier above turning on the faucet, sending water clinking and whooshing down the pipes. ‘It’s too loud, gets on your nerves. I can’t stand it – I start to holler,’ he told Gassian. ‘Are they doing it on purpose?’

Half of them hallucinated constantly. They heard whispers and muttered sounds, which took on menacing meanings: prison guards conferring about amputating a prisoner’s leg, someone getting beaten up with sticks. One prisoner – the disconsolate historian of Sartre’s Nausea brought to life – was haunted by the inconstancy of objects. ‘Melting, everything in the cell starts moving,’ he told Grassian. ‘Everything gets darker, you feel you are losing your vision.’ Another had Alice in Wonderland-like visions, featuring pancakes of diminishing sizes delivered to his gate. Four had extended bouts of amnesia. They said they felt narcotised, and couldn’t concentrate on anything.

‘These people were very sick,’ recalls Grassian. He thought it resembled anoxic brain injury – the result of an oxygen-starved brain – or delirium tremens, suffered by dipsomaniacs in the throes of alcohol withdrawal. But the symptoms also recalled a curious set of Cold War-era experiments that Grassian had read about years before.

Through the 1950s and ’60s, researchers in America and Canada were investigating the effects of ‘sensory deprivation’ or ‘perceptual isolation’, both analogues of solitary. This work was largely bankrolled by the CIA, which was interested in developing more efficient techniques of interrogation and ‘mind control’. The Canadian neuropsychologist Donald O Hebb proposed that dramatically reduced stimuli – such as in narrow windowless cells with single beds – might be one way to impair a prisoner’s alertness, and lay the ground for ‘the implantation of new or different ideas’.

To test this hypothesis, Hebb’s colleagues at McGill University confined college students to isolation units, where ear pillows muffled their hearing, and plastic visors restricted their sight. Within 24 hours, they couldn’t think or concentrate, and experienced powerful sensorial hallucinations: they had strange visions of rocks, eyeglasses, babies, their skin crawled, and they heard choirs trilling in ‘full stereophonic sound’. They experienced spatial disorientation whenever they left their cell.

Meanwhile, researchers on a Californian army base confined soldiers to soundproof isolation chambers for four days, after which they observed that their test subjects became hyper-attentive to stimuli. ‘After the dearth of sensory experience imposed by isolation,’ they wrote, ‘[the prisoner] seems to become more responsive to any dynamic stimulus energy in his environment, actively seeking and better tolerating stimuli that are normally inadequate to attract and maintain attention.’

With this research at the back of his mind, Grassian headed to the library to search for clinical parallels of what he’d just seen, and also to research the history of solitary – something he hadn’t encountered before. ‘I saw that similar symptoms had first been seen in poliomyelitis patients in iron lungs, in spinal traction patients, or those who’d had eye-patch surgery, polar explorers…’ he told me. All these situations were analogous to solitary confinement, by reducing sensory inputs or creating isolating circumstances. But what Grassian found most staggering was his discovery that America was the earliest adopter of solitary confinement, despite its reputation as ‘the world leader in social progress’. The English philosopher Jeremy Bentham might have been the first to design the ‘Panopticon’ – a structure of remotely observed solitary cells that enforced discipline through the threat of being watched – at the tail end of the 18th century. But these ideas first found shape in stone and mortar with the opening of the Eastern State Penitentiary in Philadelphia in 1829.

Charles Dickens visited the prison in 1841, and thought its ‘slow and daily tampering with the mysteries of the brain… immeasurably worse than any torture of the body’

The ‘separate system’ was regarded a rational, humane replacement for the dark legacies of colonial law: punishments that consigned offenders to the gallows, the stock, or the public cage, which used pain and shame as deterrence. As its name and its vaulted, sky-lit cells suggested, the Philadelphia penitentiary intended to reform prisoners by enforced monkish solitude, repentance and rehabilitation. Inmates ate, slept, and worked in individual cells. They exercised in a private yard once a day, and were given a single book to read: the Bible.

The ‘separate system,’ as it became known, had impassioned admirers and critics, who battled it out in pamphlets (the message boards of the day). Charles Dickens visited the prison in 1841, and thought its ‘slow and daily tampering with the mysteries of the brain… immeasurably worse than any torture of the body’. In the same year, Reich, a clinician in southwest Germany, observed a distinct psychic malady developing among some isolated prisoners awaiting trial. ‘The prisoner becomes silent, chary of words, lost in brooding,’ he wrote in 1871. ‘He observes little of what goes on about him and remains motionless in one spot. His face takes on an astonished expression, the gaze is vacant and indefinite.’ With prolonged isolation, the condition worsened. ‘Consciousness becomes more and more clouded, soon illusions, hallucinations, and delusions appear… Simultaneously [the patients] complain about all kinds of bodily sensations.’ Reich called this twilit fugue state ‘prison paranoia’.

In 1890, the testimony of James J Medley, an isolated prisoner on death row in Colorado, inspired a landmark decision by Supreme Court Justice Samuel Freeman Miller, who subsequently released the prisoner. In his judgment, Justice Miller observed: ‘A considerable number of the prisoners fell, after even a short confinement, into a semi-fatuous condition, from which it was next to impossible to arouse them, and others became violently insane; others still, committed suicide; while those who stood the ordeal better were not generally reformed, and in most cases did not recover sufficient mental activity to be of any subsequent service to the community.’

Yet, just as Grassian was researching the history of solitary and its associated ills, the US prison system was strengthening its faith in this form of incarceration, building, in every state, multimillion-dollar citadels composed of single-cell ‘control units’: super-maximum-security prisons, or supermaxes, for short.

Supermaxes are high-tech panopticons built to fulfil the Benthamite objectives of ‘punishing the incorrigible’ and ‘reforming the vicious’ or, in contemporary policy-speak, ‘managing risks efficiently’. Constructed after a decade of riots and prison-guard slayings, these free-standing facilities entirely composed of single-cell units are designed to minimise contact between prison guards and inmates. Of the 81,600 prisoners in solitary today, approximately 25,000 are in supermaxes. While the majority of America’s isolated prisoners are routinely moved in and out of the solitary confinement wards of regular prisons, supermaxes are entirely given over to the long-term containment of a specific set of prisoners: those on death row, and those deemed violent, disruptive or given to escape attempts. In the press, such prisoners are typically described as ‘untameable’ (by popular conservative commentator George Will in 1997), ‘predatory, problematic and influential’ (by three prison wardens in the Wisconsin State Journal), and ‘the most devious and manipulative’ violent offenders (by Gerald Berge, a supermax warden, for the journal Corrections Today in 2001).

Supermaxes embody a transition in prison policy over the past 30 years, from rehabilitation to a punitive ideology that emphasises stricter regulations, harsher punishment, and tougher sentences. They are carceral citadels that recall army bases with their remote locations and soaring electrified perimeter fences, and they star in a kind of security theatre intended to make the public feel safer. Inside, cells are typically laid out in narrow rows radiating from a central tower. From these eyries, correctional officers control the doors, lights, and temperatures of every unit. Prisoners spend 22.5 hours a day in 8ft x 10ft windowless isolation units, with 1.5 hours’ recess by themselves in a small concrete pen. Verbal communication takes place over an intercom system, and moments of contact are fleeting and often brutal: prisoners are put in security restraints or subjected to ‘cell extractions’, forced out of their cells by officers in riot gear and shock shields, armed with tasers and pepper spray.

America got its first proto-supermax in 1934. This was Alcatraz Federal Penitentiary, a military prison-turned-maximum security facility on an island in the San Francisco Bay, intended to house ‘the worst of the worst’. In 1941, the warden designated Block D, an isolation unit, for troublemakers inside the prison, the worst of the worst of the worst. When ‘the Rock’ shut shop in 1963, United States Penitentiary Marion was opened in southern Illinois to ‘confine not only some of the incorrigibles from Alcatraz but several hundred other difficult, escape-minded young inmates’. In 1973, ‘control units’ were built for the most violent of these ‘incorrigibles’. After two inmates stabbed and killed two prison guards on 22 October 1983, the prison was put on ‘lockdown’ for 23 years. Prisoners were isolated in their cells for 23 hours a day, and they were denied exercise and communal dining. This sparked off the ‘Marionisation’ of prisons around the country, and effectively turned USP Marion into the country’s first supermax facility.

In 1989, a sprawling concrete bunker started to take shape in California, amid a stand of redwoods near the state’s coastal border with Oregon. Bounded by an electric perimeter fence, Pelican Bay State Prison was the country’s first official supermax, intended for California’s ‘most serious criminal offenders’. States across the country followed suit. Between 1995 and 2000, the number of prisoners in supermax beds soared by 40 per cent nationally, to 20,000 – almost 1.8 per cent of the number of prisoners serving more than a year’s sentence in both state and federal prisons. This upward tick was mirrored in the number of prisoners being consigned to solitary. Between 1995 and 2000, according to a report by the Bureau of Justice Statistics, the number of prisoners in ‘restrictive housing’ also soared by 40 per cent nationally, outstripping the overall growth rate of the prison population, which increased by 28 per cent in the same period. By 2004, 44 states had some form of supermax housing, and the number of inmates in them had risen to its present-day tally of 25,000.

The numbers are notoriously difficult to track. Not all supermax-type facilities are classified as such, and in prisons and jails, solitary confinement goes by various appellations. Inmates can be sent to ‘disciplinary segregation’, which is incurred whenever a hearing officer from the Department of Corrections judges that an inmate has committed a disciplinary infraction. ‘Administrative segregation’ is the prison official’s destination of choice for gang members and the politically active. ‘Protective custody’ is ostensibly for prisoners’ protection, but it’s otherwise indistinguishable from the other categories. ‘Suicide watch’ can be worse than other types of isolation, because prisoners are stripped down to their shorts and put in a kind of padded mini-Box (known in California as the ‘rubber room’). ‘Keep-lock’ is confinement that takes place amid the general population, usually before being consigned to the Box for a rule violation, or before a transfer to another correctional facility.

In the public imagination, these sentences are handed to ruthless mass-murderers on death row, not a humble stoner such as King, or the perpetrators of the kinds of offences enumerated in inmate misbehaviour reports: collecting too many stamps; possessing ‘contraband’ such as phone cards or nail varnish, or condiments such as pepper or curry powder; refusing to return a food tray; declining to submit to a urine analysis test; spitting on a correctional officer; erecting a makeshift ‘privacy curtain’ in order to perform ablutions out of a bunkmate’s sight; inflicting self-harm.

They hallucinated, threw faeces at the guards, and howled through the night; in response, they received punishment, not treatment

As heterogeneous as supermax facilities are, they have a few things in common. They all cost two or three times as much to construct and maintain as maximum-security prisons, and prisoners released directly from them – and restricted housing circumstances in general – are found to have an elevated chance of finding their way back, particularly through violent recidivism. One judicial report in 2012 quoted the University of Albany criminologist Hans Toch, who said that prisoners ‘may become the “worst of the worst” because they have been dealt with as such’.

In recent years, supermaxes have incited a number of lawsuits for being dirty, dangerous, and for having inadequate mental health services. Terry Kupers, an Oakland-based forensic psychiatrist, has evaluated the psychological conditions of hundreds of isolated prisoners for several such lawsuits filed by the American Civil Liberties Union (ACLU) against prison authorities. A recent case involving death row inmates in Unit 32, a supermax facility in Mississippi State Penitentiary at Parchman, sparked off a change of heart among prison officials, and something of a national trend. When Kupers evaluated the residents in Unit 32 in 2002, which reeked of malfunctioning toilets, he found that about 100 of them had severe undiagnosed or misdiagnosed mental illnesses. They hallucinated, threw faeces at the guards, and howled through the night; in response, they received punishment, not treatment. After listening to the accounts of inmates who described the facility as a hellhole and insane asylum, the prison authorities gradually reduced the segregated population from 1,000 to 150, upon which violence plummeted by 70 per cent.

The Mississippi experience led to a re-examination of the rationale behind solitary confinement in Colorado, Illinois, Maine, Ohio and Washington. Maine cut its segregated population by almost 60 per cent, and made it onerous to keep a prisoner in confinement for more than 72 hours. The Colorado prison authorities reviewed their segregation practices and, in 2012, announced the closure of a 316-bed administrative segregation unit that will save the state $13.6 million this year. This January, prison authorities in Illinois closed down its notoriously repressive supermax, Tamms Correctional Center, which cost the state $26 million annually, or about $64,800 per inmate per year to run.

Half the successful suicides in prison happen in solitary

In June 2012, in a packed hearing held before the Senate Subcommittee on the Constitution, Civil Rights and Human Rights, Senator Richard Durbin of Illinois spoke out against solitary confinement, and engaged in a fiery debate with the director of the Federal Bureau of Prisons. The Senate was shown a life-size replica of a 7ft x 10ft SHU, and heard the testimony of former isolated inmates and prison officials in Mississippi. In February 2013, the Federal Bureau of Prisons announced that it was undertaking an audit of the practice; by November, it had announced it would visit 13 isolation units during 2014. This February, following a lawsuit by the New York Civil Liberties Union on behalf of three inmates who’d been in solitary, New York state agreed to curb the widespread use of isolation in the case of prisoners who were pregnant, or developmentally disabled, or under the age of 18. As this essay is published a second Senate Committee Hearing on solitary confinement is in motion.

‘Half the successful suicides in prison happen in solitary,’ Kupers told me over a Skype interview, despite only 3 to 6 per cent of the prison population being held in isolation. ‘It is such a stunning correlation that it is difficult to not conclude that there’s something about solitary confinement that exacerbates suicidal tendencies.’ This finding was replicated in a study published in the American Journal of Public Health this month, in which the correctional psychiatrist Fatos Kaba and colleagues analysed about 244,699 jail admissions New York City between 2010 and 2013, and found that although 7.3 per cent of prisoners admitted during this period were consigned to solitary, this group accounted for 53.3 per cent of acts of self-harm, and 45 per cent of potentially fatal acts of self-harm.

In a 2008 study in Psychiatric Services, the psychiatrists Raymond Patterson and Kerry Hughes analysed admissions between 1999 and 2004 in the California state prison system – the largest in the country – and found that nearly half of successful suicides occurred in single cells in administrative segregation or ‘secure housing units’, while another 12 per cent took place in mental health crisis beds. That chimes with a 1997 study by psychologists Holly Miller and Glenn Young which found that prisoners’ symptoms of mental distress rose in concert with the severity of their segregation. It also echoes a 2008 study in Criminal Justice and Behavior by David Lovell, who found that nearly half of all isolated prisoners in a Washington State supermax prison had serious mental illness or brain damage.

Such studies still leave important questions unanswered: does solitary draw in an especially vulnerable subgroup of prisoners? Does isolation damage or transform the brain? Or both?

Grassian is convinced that both are true – the first, from his research, and the second, from his experiences visiting hundreds of prisoners in isolation units across the country. ‘Punish him, punish him, punish him: that’s the only thing the correctional system knows to do,’ he told me. But the kind of prisoners who tend to be in solitary don’t respond to a rational calculus of means and ends and ‘that paradigm holds valid for an exceedingly small fraction of the prison population.’ His research and observations have lent strength to several important federal court decisions, including the landmark 1995 case Madrid v Gomez, in which the court called for the removal of prisoners with psychiatric problems from isolation, and the judge conceded that the conditions in SHUs ‘may well hover on the edge of what is humanly tolerable for those with normal resilience’.

In 1999, Grassian went on a tour through the SHU of Attica, a maximum-security prison in upstate New York, which brought that message home especially forcefully. In cell after cell, there emerged characters who belonged in a Romantic painter’s depiction of a madhouse: ‘Some guys were masturbating openly. Some guys were screaming,’ Grassian told me. He remembers turning on his companion, a lawyer for the Department of Corrections, and ‘growling’ at him: ‘You’re looking at the population of a state psychiatric hospital. This isn’t the “worst of the worst”. This is the sickest of the sick!’

Billy Blake has spent the past 27 years being hot-boxed with those sickest of the sick. In 1987, at the age of 23, he shot two deputy sheriffs escorting him to a hearing. One was wounded; the other died. Since then, he’s been bounced along from Box to Box at different maximum-security prisons in remote corners of upstate New York, until reaching his present abode: the SHU of Elmira Correctional Facility. Within this high-security pen perched on a small hill overlooking the town’s cemetery, behind two soaring fences glinting with concertina wire, Billy resides in a place that thousands, like King, are anxious to put out of their minds.

Billy, who has lived this way for more than half his life, perceives boredom in the multispectral way that the mantis shrimp, which has a dozen receptors, sees colour. In an essay entitled ‘A Sentence Worse Than Death’ (2013), he wrote:

You probably think you understand boredom; know its feel, but really you don’t. What you call boredom would seem a whirlwind of activity to me, choices so many that I’d likely to be befuddled in trying to pick one over all the others. You could turn on a movie or some other show; I haven’t seen a TV since the 1980s. You could go for a walk in the neighbourhood; I can’t walk more than a few feet in any direction before I run into a concrete wall or steel bars.

Billy knows ‘bug-outs’ just as intimately. He’s come dangerously close to becoming one himself, as he tells me when we meet in the visiting room of Elmira’s SHU. (He’s permitted a single visit a week, so we coordinate it over letters, weeks in advance.) Billy is a trim, sinewy-faced man wearing black prison boots and a petroleum-green prison uniform, which, he informs me with pride, conceals six-pack abs. A snack machine rumbles in a corner, and facing us, on an elevated concrete plinth, is a correctional officer the colour of fresh factory-farmed beef, poring over a newspaper while he pretends not to listen. He pretends well; Billy’s voice is, as he declares, ‘mad loud’ even to his half-deaf 90-year-old father, thanks to all these years trying to make himself heard over the standard issue SHU din.

‘In Sullivan [in Fallsburg, NY], my neighbour was this dumpy boar-headed Cuban kid who’d run his mouth at the gate 24/7,’ Billy says. ‘I had to stuff wet toilet paper in my ears all the time to block him out. Them gates were all there were between him livin’ and dyin’.’ Billy takes an energetic bite of a snack-machine pork-pizza and says: ‘Once, we were both at the gate, shouting at each other for hours, saying the most despicable shit, when I suddenly got so enraged, it felt like an out-of-body experience. I probably looked like a cherry with veins. I felt like I was floating. I was sweating, my heart beatin’ in my ears: Boomp! Boomp! Boomp! I told myself, “You’re buggin’ the fuck out!”’

After weeks of sleeping in snatches, he staggered out into the yard during recreation time and built a small mound of snow to sleep in for an hour

One winter in Shawangunk, in Ulster County, NY, two inmates on either side of his cell devised a simple game. From morning to night, as Billy watched, envelopes of excrement went from one side to the other, careering past his cell like hockey pucks flying into a revolting space-time dimension. Most of the projectiles landed, and remained, just outside his cell door. After several days, he yelled: ‘If you have a beef with each other, go at it like men. Don’t do this bozo shit!’ There was a pause, and one of them screamed: ‘Mind your business!’ The other one shouted: ‘This uppity cracker got to pay!’ They came up with a new game. For five long weeks, they tirelessly banged on Billy’s cell with their sneakers. When meal trays arrived, they took turns eating so there’d be someone to keep up the rattling and pounding. At night, they slept in shifts. ‘It shocked me out of my dreams so many times, that THUD-THUD-THUD!’ Billy recalls. After weeks of sleeping in snatches, he staggered out into the yard during recreation time one morning and built himself a small mound of snow to sleep in for an hour. ‘That was the most I’d gotten in weeks without being shocked awake by the CA-RACK! of a sneaker,’ he says.

The sickest neighbour Billy ever had was in Great Meadows Correctional Facility, which the inmates called Comstock. Danny, a Barbados-native, was so sick and suicidal that the correctional officers had removed everything from his cell, even the mattress and bedclothes, and they’d put him in a waist chain and shackles. ‘Danny was 6ft 11in,’ Billy recalls, ‘and you could see every rib. He looked like a skeleton with a black tarp pulled around him.’ He was ‘on the loaf’: a punitive diet of meatloaf and cabbage, which he ate twice a week. ‘The rest of the time,’ Billy says with a grin, ‘he’d mix it with shit and piss and put it in a pile at the back of his cell. The Plexiglas window of his cell was smeared with shit.’

Billy has committed two inmate registration numbers to memory: his own and this poor wraith’s. ‘You know why?’ he says eagerly. ‘You know the word “verbigeration”? It’s what bug-outs like Danny spend their time doin.’ He had a booming voice, he’d say ‘Danny D Jordan D Danny Jordan 77A4527 Comstock Great Meadow Correctional Facility 12821 St Petersburg Speightstown Barbados 19226…’ over and over from breakfast to dinner and all through the night.’ There were no pauses, Billy adds: ‘Bug-outs only catnap.’ After a month had passed, and Danny finally fell silent, a voice in Billy’s head intoned: ‘Danny D Jordan D Danny Jordan 77A4527…’ ‘I told myself: “Billy! You’re losing it!”’ he says, laughing. ‘Now tell me that ain’t insane!’

Unlike Danny, the Cuban, and the two shit-slingers, Billy sounds far from insane. But the Box, with its stress and monotony, has been slowly, inexorably reshaping all their brains.

You are where you live. How you live shapes who you are. We owe a debt to the Canadian neuropsychologist Donald O Hebb for proving these aphorisms right down to the neurone. In 1947, Hebb took a few rat pups home for his children to play with. When these pups grew older and hairier, and were less welcome darting about the furniture, he brought them back to his McGill University lab, where they outsmarted cage-reared rats in problem-solving tests. They were also visibly well-adjusted, unlike cage-bound compatriots who groomed themselves until their whiskers dropped off, and had balding patches all over their bodies.

During the 1960s and ’70s, researchers at the University of California, Berkeley, followed up on Hebb’s intriguing observation with controlled experiments in the lab. The neuroscientist Mark Rosenzweig showed that, when compared with rat packs that roved in rodent McMansions filled with ladders, tunnels and toys, animals that languished in spartan, supermax-style cages had fewer connections between neurons and thinner cerebral cortexes. Marian Diamond, a colleague of Rosenzweig, showed that various types of enriched or impoverished environmental exposures could alter the dimensions and even the cellular content of the cortex at any age from newborn to elderly. Even four days of impoverished environment could have an impact on the physiology of the cortex and its ability to navigate the world.

These were stunning discoveries. The cerebral cortex, what we refer to as ‘grey matter’, is the part of the brain that makes us most human. This dime-thick, intricate surface runs across the two hemispheres of our brain. It’s where we make our plans, guide our movements and consciously respond to social cues. It’s where stimulus turns to perception, where the neural nuts-and-bolts of language reside. The Berkeley experiments showed that, at least for rats, social interactions and surroundings are inscribed in the neurophysiology of the brain, and not just during the early part of life.

As years passed, an irrefutable body of work in a range of species established that social interactions across complex terrain could nourish and boost the brain, while impoverished surroundings diminished it in every stage of life. By the 1980s, the neuroscientist Fernando Nottebohm of Rockefeller University was reporting the growth of new neurons whenever adult songbirds learnt new songs. Later, he examined the sea-horse-shaped hippocampus, a seat of spatial memory, in the brains of adult black-capped chickadees. Captive chickadees, he found, generated fewer new neurons in their hippocampi compared with counterparts from the wild.

By 1998, a team at the Salk Institute in California had connected social interaction and play to improved episodic memory and mood – and enhanced desire to venture out and explore. To do their work, the Salk team corralled 12 mice in a lavishly equipped cage fitted with tunnels, toys, and a running wheel, while a control group of four mice were consigned to a plastic box shanty. A month later, the mice were thrown into a Morris maze – a circular tub of water with a submerged platform in the middle. Those who’d had the benefit of play facilities managed to locate the resting spot more rapidly than their deprived peers. Meanwhile, two matching groups of mice were injected with a chemical marker that stained new neurons red. Compared with their confined counterparts, mice in the enriched environment had hippocampi teeming with many more brain cells, including neurons and astroglia, which help new neurons survive. Of special note, the enriched mice had 57 per cent more new nerve cells in their dentate gyrus – a corner of the hippocampus that helps consolidate episodic memory, control depression and stress, and spur exploration of new environments.

But what was it about isolation and confinement that caused the brain to become impoverished? In 2004, the Princeton neuroscientist Elizabeth Gould and postdoctoral researcher Alexis Stranahan inadvertently stumbled upon a clue while investigating a paradox: exercise was known to release stress hormones that should tamp down on neural growth. Yet a raft of studies consistently showed that exercise was a fail-safe way of enhancing the growth of new neurons in the adult brain.

To investigate, Stranahan and Gould took adult rats, housed separately, and had them scrabble around running wheels. Then Stranahan killed the rats and examined their brains under the microscope. She was dismayed to find no increase in neurogenesis in spite of the exercise. ‘Not only that, she saw an opposite effect,’ Gould told me. ‘The running animals were showing a reduction in neurogenesis.’ When Stranahan consulted the studies she’d been trying to replicate, she saw that all prior test subjects had been group-housed.

On closer scrutiny, Gould and Stranahan found that when the adult rats who’d been isolated ran, their brains were flush with elevated levels of the stress hormone corticosterone – the rodent analogue of the human stress hormone cortisol, produced by the adrenal gland. Isolation had caused levels of the hormone to spike so high that, instead of proliferating, neurons were dying off. In fact, the isolated rats’ brains could spawn new neurons only when stress hormones were forcibly lowered by removing the adrenal glands. ‘It shows that when animals live alone, they’re not very good at coping with a challenge [such as running] to the system,’ says Gould.

Shriveled dendrites in the hippocampus have also been observed in humans suffering from dementia, chronic depression, schizophrenia and PTSD

At the root of all of this, it turns out, is stress itself. Under normal circumstances, the brain keeps stress in check through an intricate set of feedback loops between the endocrine, nervous and immune system. We owe this balance, a state called ‘homeostasis’, to a set of unseen thermostats humming within us, maintaining stability through adjustments to such setpoints as body temperature or the oxygen levels of our blood. But when the environment throws a wrench in the works, another system comes into play. The core conductor here is what neuroscientists call the hypothalamic-pituitary-adrenal (HPA) axis, a network of organs fuelling our most ancient, atavistic urges: to fight or take flight.

When something triggers a fire alarm, the almond-sized hypothalamus deep within the brain dispatches an urgent message to the adrenal glands atop the kidneys, which respond by seeping out the stress hormone adrenalin. This speeds up the heart rate, flushing more blood into muscles and organs, and sending oxygen billowing into the lungs and the brain, keeping us alert and sharpening our senses. These processes encourage us to meet our challenges head-on, whether it’s getting out of bed, fleeing a predator, or conducting an orchestra.

If the threat continues, the hypothalamus releases a substance called corticotrophin-releasing factor. This rushes to the pituitary, a tiny gland at the top of the brain, which in turn, produces adrenocorticotropic hormone (ACTH). ACTH surges to the adrenal glands, which release another stress hormone, cortisol, into the blood. Cortisol converts protein to fat, catalysing the production of energy and releasing minerals from our bones. This makes up for the energy we lost in the adrenalin rush, and it also makes us active and hungry. Meanwhile, after the threat has passed, a calming infusion of neurotransmitters – serotonin, dopamine, noradrenaline – flows to temper the stress response, and restore homeostasis once again.

A little stress-induced cortisol is actually good for you. It reins in the immune system, controls inflammation, and keeps you alert and energised in the morning when its levels are naturally high. But when stress is chronic, the ebb and flow of stress hormones becomes a steady, unceasing seep. The hippocampus is not able to shut down the stress response, leading to weakened immunity, demineralised bones, clogged and narrowed arteries, obesity, impaired memory and cognition, and a susceptibility to psychological problems. Chronically depressed people are likely to have too much cortisol sloshing around their brain through the day, while sufferers of post-traumatic stress disorder (PTSD) – and residents of the Box – likely owe their constant state of hypervigilance to overpowering doses of noradrenaline.

Some of the most crucial discoveries about how stress affects the brain – particularly memory and cognition – were made in the Rockefeller University lab of the neuroendocrinologist Bruce McEwen. In the mid-1990s, McEwen and colleagues subjected adult rats to ‘restraint stress’, cramming them into cylinders resembling miniaturised iron lungs for six hours a day over the course of thee weeks. For the rats, this was pretty much the same as a shot of rat-cortisol to the brain: stress induced by isolation and restraint withered the dendrites (the connecting structures responsible for communication between neurons) in the hippocampus, a seat of memory.

In another experiment, stressed rats and calm rats were set adrift in a watery eight-armed maze, with a peanut at the end of every arm. The stressed-out rats were less deft at recalling the location of the food, leading researchers to conclude that stress impaired their spatial memory. There was another twist: in the youngest animals, shrinkage of the dendrites reversed when stress abated. In middle-aged animals, the reversal was just partial, and in the oldest animals, there was no evident reversal at all. Shrivelled dendrites in the hippocampus, McEwen points out, have also been observed in humans suffering from dementia, chronic depression, schizophrenia and PTSD.

Recent findings suggest that chronic stress can lay down intransigent memories as well – especially those associated with aggression, violence or fear. In a 2005 study, McEwen compared young adult rats stuffed into airless plastic bags two hours a day for 10 days to counterparts stuffed into the bags for two hours, just once. Afterwards, under the microscope, the brains of the chronically stressed-out individuals had bushy nerve branches snaking around the amygdala, a corner of the brain that forms long-lasting fear memories.

Human loneliness, however unremitting, can’t be replicated by a rat squeezed into a plastic bag. But McEwen says the effect is evolutionarily conserved. In the face of isolation, measures of brain function and neuroimaging should show the same abnormalities, no matter what the species involved. McEwen says these irregularities are likely to cluster in a number of places. The hippocampus – where memories, including spatial memories, are stored – is likely to be diminished in size. The amygdala – which perceives threats and records fearful memories – is likely to get bigger and more hyperactive as it drives states of anxiety and depression. Meanwhile, the prefrontal cortex – which controls activity in the amygdala, as well as heartbeat, behaviour, and aggressive impulses – might lose neural cells and dwindle in size.

Hundreds of human studies show that even mild isolation can be a high-speed motorway to poor health – worse immunity, worse sleep, worse inflammation in the young, and higher rates of hypertension and cardiovascular trouble among the old. In 2002, epidemiologists at University College London studied 240 middle-aged civil servants and found that lonelier people had stress-associated increases in blood proteins and white blood cells that put them at higher risk for narrowed arteries, strokes, and hypertension. In 2012, a team of biochemists and gerontologists in Dublin measured both loneliness and blood glucose levels in 466 elderly people; the loneliest had the highest blood sugar levels, and a propensity to obesity and Type-2 diabetes.

Other studies connect social isolation with neuropsychiatric ills. In 2007, neurologists at Rush University in Chicago studied 823 elderly people and found a connection between loneliness and cognitive decline: the risk of Alzheimer’s disease more than doubled among the loneliest of the group. In several experiments, psychologists studied isolation resulting from social rejection in teens. The excluded were more aggressive, less willing to exercise self-control, and had diminished cognitive abilities in tasks that required recollection and use of complex information.

Isolation puts prisoners at risk of anxiety, panic, chronic depression, rage, loss of control, paranoia, hallucinations, self-mutilation

Craig Haney, one of the leading correctional psychologists in the US, has testified to the psychological impact of solitary confinement on prisoners numerous times, including in the 2012 Senate hearing in Washington DC. In the course of his work over two decades, Haney has found that isolation puts prisoners at risk of a range of adverse symptoms: appetite and sleep disturbances, withdrawal, hypersensitivity, anxiety, panic, chronic tiredness and depression, rage, loss of control, paranoia, hallucinations, self-mutilation, and suicidal ideation and behaviour.

Yet existing research, including Haney’s own study of 100 prisoners in isolation in California’s Pelican Bay, have been constrained by ‘ethical, legal, and practical barriers’. A truly randomised controlled study is nearly impossible to recreate in the context of a prison, because only a troop of white-coat Caligulas would feel comfortable arbitrarily assigning some participants to solitary and some to the general population. On the rare occasion in 2010 that a prison granted access to researchers, the resulting study drew an unlikely conclusion: inmates actually appeared to get better during a one-year stint in solitary, at least initially.

Funded by the Department of Justice, and conducted by Maureen O’Keefe, the lead research director at the Colorado Department of Corrections, the study set out to assess how 270 prisoners fared over a year in Colorado State Penitentiary, a supermax in Cañon City. The first assessment was made, by self-report, when the inmates were held in temporary segregation after they’d being charged with breaking prison rules, and had faced an internal hearing to decide whether they’d be assigned to segregation. Some of them returned to the general population, some were sent to a facility for prisoners with psychiatric conditions, and others wound up in isolation. Over the rest of the year, prisoners from all three groups responded to questionnaires about their psychological states five more times. The conclusion was that all three groups improved at first, but then coasted without change to the end.

Haney, Kupers and Grassian denounced the study for pandering to the interests of the correctional authorities, but the study’s authors and advisers are quick to point out its limitations as well: inmates were initially assessed during a tumultuous time, when they’d fought with someone, or had been attacked – which made for an unnaturally elevated baseline. The prison didn’t have protective custody at the time of the study, so some inmates, rather than feeling oppressed, might have been relieved about being inaccessible to would-be assailants. And though hardly a resort, the prison was better serviced than some other facilities, since its inmates had a TV and a ‘STEP’ programme that rewarded good behaviour with privileges, which might have fostered some hope, possibly even a sense of agency.

Jamie Fellner, a psychiatrist who works on criminal justice issues with Human Rights Watch and oversaw the study, told me: ‘The atmosphere and culture of a prison has a lot to do with the impact. How many phone calls do you get, how long do you get, what do you think your chances are of staying out of solitary. That’s something we didn’t address.’ Joel Dvoskin, a psychologist also involved in the study, averred: ‘It’s one study, in one prison system, and each system is unique, so it’s not clear how generalisable it is. One harmful or skilful shift commander can change the entire environment in a prison, including a segregation unit.’

In a strong rebuttal to the study published in the Correctional Mental Health Report in 2011, Grassian and Kupers point out that self-reports are an unreliable measure of prisoners’ mental states, especially when they don’t take into account inmates’ prior mental health history, and aren’t backed by clinical reports. Not only do self-reports call for lucidity and self-awareness, which might be diminished among prisoners with mental health conditions, but they can be believed only if prisoners are safe from potential repercussions affecting future parole hearings or their prospects of being released from solitary.

Grassian and Kupers cite a specific example associated with the study itself. In 2008, an inmate enrolled in the study committed suicide despite the fact that, just prior to the incident, his self-report recorded no signs of distress. Kupers and Grassian insist that the study disregarded evidence of the prison’s toxicity, including 37 emergency psychiatric contact reports for inmates in solitary during the course of the study compared with just three such reports among inmates in the general population.

The larger problem, Haney told me, is that the most toxic solitary cells remain out of bounds for researchers, and that any brain scans to prove a link between solitary and brain damage would, in this context, be a fanciful prospect. ‘Absent a judge telling a prison system that it “must” allow access by outside experts, few are willing to grant it, even for the purpose of interviews,’ said Haney, who obtained most of his access through court orders. Just as with the Colorado study, the nature of that access has opened the impartiality of his work to question as well.

Complete answers will come only when more empirical research can be done. That might be a long way off, for all the reasons Haney suggests. But another set of Boxes is already being reformed, on the knowledge we have in our hands today. About nine months ago, Alex Dranovsky, a neuroscientist at Columbia who studies isolation and its effect on the brain, was surprised to hear that his university’s Animal Care and Use Committee had amended its guidelines, and now forbade researchers from keeping animals alone in cages unless isolation was specifically part of the experimental design. This is in addition to rigorous scrutiny that review committees pay to the animals before every experiment, and periodic laboratory inspections. ‘Well, I guess isolation is the cruellest thing we do to animals right now,’ Dranovsky told me.

Meanwhile, every year, thousands of inmates leave solitary cells to join the ranks of parolees outside prison, their minds altered by an experience so fraught with risk that scientists require special dispensation to do it to animals.

Some of the names in this article have been changed.