If you are assigned to a death row unit in a prison, the chances are that you have committed a particularly serious crime. It is also very likely that you have suffered some damage to your cerebral cortex. This was the shocking conclusion reached years ago by psychiatrist Dorothy Lewis and neurologist Jonathan Pincus when they set out to study the biographical and neurological details of 29 death row inmates.
Violent crimes and homicides committed by ordinary people – that is, those that are not the result of war, terrorist attacks or similar intrigues – are most often the result of the triggering of what is known as affective aggression (also known as impulsive or reactive aggression). This is the type of aggression that results from the activation of an anger impulse, orchestrated by deep brain regions such as the periaqueductal grey matter or the amygdala. In mammals, and under healthy conditions, anger can sometimes be very useful, as is the case with all basic emotions. In the case of modern humans, the emotional reactions that are forged in certain subcortical encephalic nuclei are pacified, softened and brought into society thanks to the intervention of the cerebral cortex and, in particular, the prefrontal cortex.
The fact that the prefrontal cortex continues to develop until after the age of twenty is one of the reasons that seem to explain the impulsiveness and lack of judgement that characterise adolescence. This behaviour is not worrying, as in most cases time will eventually produce a cerebral cortex capable of guiding us more or less rationally through our lives. However, a permanently damaged and immature cortex can pave the way for outbursts of affective aggression. When Lewis and Pincus analysed the lives of fifteen men sentenced to death in the USA, they found that all of them, absolutely all of them, had suffered some kind of serious head injury in childhood or adolescence (they had been run over or otherwise injured in accidents, falls, beatings, etc.). They did not choose these people because they suspected some kind of brain damage, but simply chose the prisoners who were closest to their execution date.
Surprised by these results, they set out to conduct a similar study on fourteen other death row inmates, in this case young people who had committed their crimes before the age of eighteen. What they discovered was once again shocking: all of these boys had suffered some kind of severe head trauma (car accidents, motorcycle accidents, car crashes, falls, etc.) and, in addition, all but one of them had suffered some kind of physical or sexual abuse in the family environment.
Death row is not just a sad place to study our brains and affective aggression. It is also one of the places where another kind of aggression, called predatory or instrumental aggression, is routinely and openly practised. This is the kind of attack that predators practise, a premeditated aggression that is not driven by anger but by cold, dry calculation. Leopards do not attack gazelles because they are angry with them, but because they are hungry, and to satisfy their hunger they devise a hunting plan. In the same way, the authorities in some countries can devise plans of predatory aggression to deliberately execute other human beings. We are one of the few animals capable of such a thing, predatory aggression against adult individuals of our own species; without, at least in principle, any kind of brain damage to the aggressors.