Many of us like to believe that all adults possess the same capacity to make sound choices. It's a nice idea, but it's wrong. People's brains can be vastly different - influenced not only by genetics but by the environments in which they grew up. Many "pathogens" (both chemical and behavioral) can influence how you turn out; these include substance abuse by a mother during pregnancy, maternal stress, and low birth weight. As a child grows, neglect, physical abuse, and head injury can cause problems in mental development. Once the child is grown, substance abuse and exposure to a variety of toxins can damage the brain, modifying intelligence, aggression, and decision-making abilities.
Reading this, one might think that Eagleman is arguing that one can never be held accountable for anything, but that really isn't the case. He's arguing that our justice system should take into account the state of the brain, its physical make-up as well as the psychological influences that shaped it, and that punishment or rehabilitation should be planned accordingly. This is a very humanistic approach to the concept of justice. It's one that a society still stuck, as ours seems to be, in the "eye for an eye" stage of psychological maturity - or lack of maturity - is probably unable to accept or even consider. But Eagleman has put the idea on the table, and perhaps at some later, more enlightened time, it might even become our normal way of dealing with such issues.
David Eagleman writes with clarity and wit and constantly introduces anecdotes from current events to illustrate his points. This is a very accessible book about the most complicated of subjects, our internal computers. Interesting to find out that, for the most part, those computers travel with us, Incognito.