There is a difference between loneliness (the imposition of ) and aloneness (the choice of being alone), and thus the brain reacts in very different ways. Loneliness, or social isolation, affecting a large part of the population as it became an epidemic in the last few years, is known to cause changes in the brain, possibly leading to more serious consequences such as and other mood disorders. However, some of those changes can be reversed if the appropriate social interactions are re-established and the person reengages in social activities.

But what if the person doesn’t have that option?

We are talking about solitary confinement, a form of imprisonment still practiced in many countries, including the U.S.

Robert King, an ex-inmate who was in solitary confinement for 29 years, shared his experience with a room full of curious neuroscientists during the world’s biggest conference by the Society for Neuroscience in November 2018. Being confined in a 6x9-foot cell for almost 30 years, with very limited contact with other humans or physical exercise, surely has consequences on one's overall health, including the brain. King knew that solitary confinement was changing the way his brain worked. When he finally left his cell, he realized he had trouble recognizing faces and had to retrain his eyes to learn what a face was like. His sense of direction was also messed up, and he was unable to follow a simple route in the city by himself. It is as if his brain had erased all those capabilities that were no longer necessary for survival in a cell no bigger than the back of a pick-up truck.

One of the most remarkable effects of chronic social isolation, as in the extreme case of solitary confinement, is the decrease in the size of the hippocampus, the brain region related to learning, , and spatial awareness. The sustained of extreme isolation leads to a loss of hippocampal plasticity, a decrease in the formation of new neurons, and the eventual failure in hippocampal function. On the other hand, the amygdala increases its activity in response to isolation. This area mediates and , symptoms enhanced in prisoners in solitary confinement.

Studies on mice have shown that one month of social isolation caused a decrease of around 20% of the total volume of neurons, though researchers saw that remaining neurons were branching out more than those mice that were not isolated. When the isolation went on longer — up to three months — researchers saw that the extra branching of the neurons was no longer happening, and that, in exchange, spines (structures that neurons develop to place the machinery that is required to communicate to each other) were greatly diminished. What does this mean? The branching that took place in the first month of isolation may represent some sort of compensatory mechanism that the brain puts in place in order to overcome and prevent the detrimental effects of isolation. However, when isolation went on for “too long," this mechanism seemed to come to an end, and trigger the loss of neuronal communication in the form of spine elimination.

In addition to the effects that loneliness will cause in the brain, solitary confinement also has an important component of sensory deprivation. The small cells where inmates are isolated are windowless, and though inmates are entitled to have one hour of physical exercise every day, sometimes this would not happen due to the busy schedule of the prison, King reported. The sensory deprivation contributes to important health impairments, such as alterations of circadian rhythms, the internal biological clock that regulates overall the proper functioning of our bodies.

Solitary confinement as a is closer to a form of torture, with serious consequences for neurological health. Teams of researchers are investigating further the deep effects of this practice and studying the possibility of regulating it to maintain physical activity as well as sensory input and circadian rhythms, in order to prevent profound changes in the brain.

This calls to the necessity of integrating science in law, as legislators may not recognize possible emotional injuries in the same way they recognize the physical effects of imprisonment. Lawyers and neuroscientists need to work together to understand the full consequences of dangerous practices that still take place in the system, such as solitary confinement.