That psychiatric testimony in murder trials is just so much psychobabble was demonstrated again in the Reinaldo Rivera case. The admitted serial rapist/killer's lawyers called on neuropsychiatrist Thomas Sachy to explain why their client's responsibility for his crimes was diminished.
According to MRI exams and PET scans of brain activity that Dr. Sachy showed to the jury, Rivera didn't have enough activity going on in his frontal lobes to control his anti-social violent behavior. Of course, prosecutors had experts who said otherwise - thus thoroughly confusing the jury.
Such testimony is usually just disregarded by the jury anyway. Good. The implication of Dr. Sachy's testimony is that violent criminals are not responsible for their acts. If they aren't, who is?