THE MIND IS “TURBULENT, STRONG, OBSTINATE”, cries Arjuna dolefully in the Bhagavad Gita. Obstinate in the face of efforts to control it, and to understand it. The two obstinacies are not unrelated. The culmination of the European tradition of inquiry into the mind—ranging from Plato to Freud—is the contention that there is such a thing as the unconscious mind, a thing to whose secrets the conscious mind is not privy. The unconscious will not yield easily, certainly not to introspection or some other simple effort of the will. But that is not to say it will yield to nothing.

People have long known of the mind’s intimate connection with a particular bodily organ: the brain. The Roman royal physician Galen of Pergamon had remarked upon the connection in the 2nd century AD while working with patients who had sustained brain damage. But it has only been in the last few centuries that we have acquired the wherewithal—the use of the microscope and other observational techniques—to study the brain in its constituent complexity. Crucially, further work on brain damage from the late 19th century onwards has enabled us to map with an unprecedented degree of precision the relation between specific mental functions and specific parts of the brain. The development, as we shall see, was not a wholly unproblematic one.

Confronted with these methods, the mind began to yield at least some of its secrets to the modern world’s most reliable technique for acquiring new knowledge: the scientific method. It is a sign of our trust in this method, and the discipline it has created—neuroscience—that we express so many of our old puzzles, our old anxieties, in the vocabulary it has given us. The fear that the appearance of control and freedom in our lives is a mere illusion, the fatalism of the ancients, is now directed not at the caprice of the gods but at neurological ‘determinism’, the view that all our actions are determined by facts about our brain states and their histories, facts over which we have no control. We seek cures for the maladies of the mind—the pre-modern world’s manias, melancholy, and madness—by manipulating the condition of the brain: hence our talk of addictions, depression and cognitive impairment.