In the United States, some neurosurgeons and psychiatrists are questioning the medical and ethical validity of brain surgery experiments to control violence in prisoners.

At issue is the practice of destroying with elector-surgery parts of the brain which condition violent behaviour.

Debate has centred around treatment of a structure deep in the limbic area of the brain called the amygdala. Its thought that a faulty amygdala triggers aggression, and this could be suppressed if the amygdala is destroyed.

One of the centres at which the controversial experiments are being carried out is the California Medical Facility at Vacaville, which was set up with funds provided by the Justice Department to act as a medical screening centre for prisons in California - such as San Quentin.

A California prison psychiatrist, Doctor George Bach y Rita, has resigned from a research programme at the Vacaville centre in protest at the methods used to induce prisoners to undergo brain surgery experiments. He claims there is a subtle pressure on the prisoner to submit to the experiments in order to get a good parole report.

Other doctors have criticised the experiments because of the secrecy under which they are conducted and the fact that research grants are given partly by the Law Enforcement Assistance Administration. The doctors say this money-source lends a political motive to the experiments.

Several specialists aired their views: