As Carl Jung put it, "In each of us there is another whom we do not know." As Pink Floyd sang, "There's someone in my head, but it's not me."

The deep secret of the brain is that not only the spinal cord but the entire central nervous system works this way: internally generated activity is modulated by sensory input. In this view, the difference between being awake and being asleep is merely that the data coming in from the eyes anchors the perception.

When a male vole repeatedly mates with a female, a hormone called vasopressin is released in his brain. The vasopressin binds to receptors in a part of the brain called the nucleus accumbens, and the binding mediates a pleasurable feeling that becomes associated with that female. This locks in the monogamy, which is known as pair-bonding. If you block this hormone, the pair-bonding goes away.

The conscious mind is not at the center of the action in the brain; instead, it is far out on a distant edge, hearing but whispers of the activity.

Even while it's true that we are tied to our molecules and proteins and neurons - as strokes and hormones and drugs and microorganisms indisputably tell us - it does not logically follow that humans are best described only as pieces and parts.

We are not the ones driving the boat of our behavior, at least not nearly as much as we believe.

This is what consciousness does: it sets the goals, and the rest of the system learns how to meet them.