One of the first things that Lewis and Pincus do, then, when they evaluate a murderer, is to check for signs of frontal lobe impairment. This, the neurological exam, is Pincus’s territory.He begins by taking a medical history. He asks about car accidents and falls from trees and sports injuries and physical abuse and problems at birth and any kind of blows to the head that might have caused damage to the frontal lobes. He tests reflexes, and asks about headaches and limps and whether the left side is the same as their right side.”I measure the head circumference. If it’s more than two standard deviations below the normal brain circumference, there may be some degree of mental retardation, and, if it’s more than two standard deviations above, there may be hydrocephalus,” Pincus told me. “I also check gross motor co-ordination – ask them to spread their fingers and hold their hands apart, and I look for choreiform movement, discontinuous little jerky movements of the fingers and arms.”We were in Pincus’s small, cluttered office at Georgetown University Medical Center in Washington, DC and Pincus, properly professional in a grey check suit and a dark-red waistcoat, held out his hand to demonstrate. “Then I ask them to skip, to hop,” he went on, jumping out of his chair to demonstrate, hopping up and down in a small space on the floor between papers and books.Pincus is well over six-feet, with the long-limbed gracefulness of an athlete, and he plays the part of neurologist to perfection: calm, in command, with a distinguished sprinkle of white hair.

At the same time, though, he has a look of mischief in his eyes, a streak of irreverence that allows him to jump up and down in his office before perfect strangers. It’s an odd combination, like Sigmund Freud being played by Walter Matthau.At one point, Pincus held up a finger 45 degrees to my left and moved it slowly to the right “Now we’re checking for frontal functions. A person should be able to look at the examiner’s finger and follow it smoothly with their eyes. If they can only follow it jerkily, the frontal eye fields are not working properly. Then there’s upward gaze.” He asked me to point my eyes at the ceiling. “The eye should go up five millimetres and a person should also be able to direct his gaze laterally and maintain it for 20 seconds.

If he can’t, that’s motor impersistence.” Ideally, Pincus will try and back these tests up with EEG, which measures electrical patterns in the brain or an MRI scan, to see if he can spot scarring or lesions in any of the frontal regions that might contribute to impairment.Pincus is also interested in measuring judgement. He tries to pick up evidence of the inability to cope with complexity, the lack of connection between experience and decision-making so characteristic of cortical dysfunction. At this point, Pincus walked behind me, reached over the top of my head, and tapped in a steady rhythm on the bridge of my nose I blinked once, then stopped. That, he tells me, is normal.”When you tap somebody on the bridge of the nose, it’s reasonable for a person to blink a couple of times, because there is a threat from the outside,” Pincus says. “When it’s clear there is no threat, they should be able to accommodate that. But, if the subject blinks more than three times, that’s `insufficiency of suppression’, which may show frontal lobe dysfunction. The inability to accommodate means you can’t adapt to a new situation.