Psychopathic behaviour may be due to a traumatic blow to the head, especially in childhood, scientists have found.
Damage to a specific part of the forebrain can produce severe impairments in social and moral decision-making, causing remark able changes in the person's personality. While the intellect might not be affected, the damage can change an industrious person into an irresponsible drifter.
New research has shown that the effects are even more pronounced if the damage occurs when the person is very young, before they have had a chance to learn what is considered appropriate behaviour, according to a report published today in Nature Neuroscience.
One of the most celebrated cases of this behavioural change after injury was that of Phineas Gage, a railroad worker whose prefrontal cortex was damaged when an iron bar was driven through his skull as a result of a dynamiting accident in 1848.
Gage recovered from his head injuries with no apparent change to his intellect. His personality was profoundly changed, however, and he was transformed from a good worker to a layabout.
Studies of such patients since have shown that they still possess factual knowledge about social and moral standards even though they appear unable to apply this knowledge in their own lives. Things are even worse for these patients if the damage occurs at a young age, before behavioural norms are learned. Dr Antonio Damasio and colleagues at the University of Iowa described two subjects who experienced injuries before the age of 16 months to a brain area known as the orbito frontal cortex.
Both children made excellent recoveries but as they grew older they began to display behavioural problems even more severe than those of patients injured as adults. They chronically stole, lied, verbally and physically abused others and as adults they were poor parents, lacked remorse and failed to make plans for the future.
The researchers said there were no obvious environmental explanations as both had come from stable middle-class families and had well-adjusted siblings. They also said the two subjects were very like psychopaths in that they showed deficiencies in moral reasoning in tests. They seemed unable to learn about accepted standards, let alone apply them.
The researchers pointed out the preliminary nature of their data and that patients with this type of damage are rare. They hope, however, that their work may lead to insights into the origins of moral and social behaviour and possible biological causes of psychopathy.
