What are the psychological effects of “doing time”? Do harsher prison conditions create harder criminals? These are the questions that the economists M. Keith Chen and Jesse Schapiro were determined to answer. Their conclusions are sobering:

Some two million Americans are currently incarcerated, with roughly six hundred thousand to be released this year. Despite this, little is known about the effects of confinement conditions on the post-release lives of inmates. In this paper we estimate the causal effect of prison conditions on recidivism rates by exploiting a discontinuity in the assignment of federal prisoners to security levels, and find that harsher prison conditions lead to significantly more post-release crime.

This really shouldn’t be so surprising. There’s now a strong scientific consensus that impoverished environments – and there are few environments as impoverished as solitary confinement – are toxic for the brain. Not only do these conditions vastly increase the likelihood of brain disease, but they are also incredibly stressful. The worst part of chronic stress – besides the fact that it kills your neurons – is that you become incapable of mounting an effective stress response in the future. Just look at the effects of Post Traumatic Stress Disorder (PTSD). Victims not only exhibit acute sensitivity to innocuous triggers – they think every loud noise is a gunshot – but they exhibit a prolonged and elevated stress response to those same events. These leads to violent outbursts, which are also stressful. As a result, daily life becomes unbearably arduous. Chronic stress ends up becoming a vicious positive feedback loop.

So this is what we’re doing to the several million inmates of our prison system. Of course, we shouldn’t judge our penal system solely by its effects on neural plasticity. But we also shouldn’t be surprised when that system creates an enormous population of dangerous minds.

I once worked in a lab where the rats started eating their cagemates. It was bloody and disgusting. A post-doc eventually decided that there were too many rats in each cage, and that the density was stressing the rodents out. Unfortunately, these stressed out rats were too far gone: even when the population density was reduced, they still insisted on fighting each other to the death. Stress had broken their brains.