Michael S. Gazzaniga, after a long career at the top of his field, is spelling out a cautionary tale about the uses of neuroscience in courtrooms. His new book, “Who’s in Charge? Free Will and the Science of the Brain,” will be available November 15, 2011.
In recent years lawyers have begun to present brain images as evidence, usually to mitigate responsibility for a crime or to test veracity of testimony, as in a polygraph; increasingly, those images have been admitted. And more are coming: In imaging studies, for instance, neuroscientists have identified cortical areas that are highly active when people suppress impulses or other behaviors.
But there are clear shortcomings in the application of each of these methods in courtrooms. Brain images are snapshots, for one thing; they capture a brain state at only one moment in time and say nothing about its function before or after. For another, the images vary widely among people with healthy brains — that is, a “high” level of activity in one person may be normal in another. Can brain science tell exactly where automatic processes end and self-directed “responsible” ones end?