A person living in an inner city area of London may have a completely different brain from a person living in the suburbs

Dr Richard Davidson

Psychologist Richard Davidson, from the University of Wisconsin-Madison in the US, suggests that problems in a single brain area may be preventing the normal human reaction which "reins in" violent urges when these are triggered by emotions like fear and anger.

This "short circuiting" can be clearly seen in brain scans, he said.

Writing in the journal Science, he said: "We suggest that individuals predisposed to aggression and violence have an abnormality in the central circuitry responsible for these adaptive changes."

Many murderers

Davidson's work is a review of research by dozens of other leading figures, who have examined between them 41 murderers defined as suffering from "aggressive impulse personality disorder".

He told BBC Radio 4's Today programme: "The brain circuitry that has been affected is crucial to the regulation of negative emotions."

He said that it was not known to what extent the changes were genetic, and to what extent created by the environment in which the individual grows up.

He said: "This are areas of the brain that are extremely modifiable by the environment, particularly the early environment."

However, Dr Harry Kennedy, a forensic psychiatrist from Dublin, told the programme: "The work doesn't show what it says, which is the difference in capacity to suppress negative emotion, it may simply show a difference in the motivation to do so."

He said that neuropsychologists could not fully explain why crimes of violence were six times more common in inner city areas than in suburban areas.

But Dr Davidson said: "A person living in an inner city area of London may have a completely different brain from a person living in the suburbs as a result of the experiences they have had."