If you had to sum up the past 40 years of research on the mind, you could do worse than to call it the Rise of the Zombies.

We like to see ourselves as being completely conscious of our thought processes, of how we feel, of the decisions we make and our reasons for making them. When we act, it is our conscious selves doing the acting. But starting in the late 1960s, psychologists and neurologists began to find evidence that our self-aware part is not always in charge. Researchers discovered that we are deeply influenced by perceptions, thoughts, feelings , and desires about which we have no awareness. Their research raised the disturbing possibility that much of what we think and do is thought and done by an unconscious part of brain - an inner zombie.

Some of the earliest evidence for this zombie came from studies of people who had suffered brain injuries. In 1970 British psychologists Elizabeth Warrington and Lawrence Weiskrantz showed a series of words to a group of people with amnesia, who promptly forgot the list. A few minutes later Warrington and Weiskrantz showed them the first three letters of each of the words they had just seen and forgotten and asked the amnesiacs to add some additional letters to make a word. Any word would do. The amnesiacs consistently chose the words they had seen and forgotten; the inner zombie, somewhere beyond awareness, retained memories of the words.

Our inner zombies may also be able to control our bodies. In 1988 a woman known as "patient D. F." suffered carbon monoxide poisoning and lost the ability to recognize objects and shapes. Her eyes were still relaying information to her brain, but the connections between regions of her brain had been damaged so that she was no longer aware of what was before her. Scientists at the University of Western Ontario set a card on a table in front of D. F. and then held up a disk with a slot in it. They asked D. F. to hold the card at the same angle as the slot. She couldn't. But when asked to put the card in the slot as if she were mailing a letter, she immediately-and unknowingly-turned the card to the correct angle and slipped it in.

These days a number of powerful new tools can scrutinize the inner zombies in healthy brains. Earlier this year, a team of University of Copenhagen researchers reported rendering 11 healthy people temporarily blind by focusing a beam of magnetism at the back of the subjects' head. This interfered with the activity of neurons in a region called the visual cortex. For a few minutes the neurons were deactivated, and the subjects reported that they couldn't see anything.

At the start of the experiment, the subjects - who could see at this point - sat in front of three lights, each with a button below it. When the center light went on, they had to reach out their hand and press the button next to it. In some trials, the scientists switched off the center light just as the subjects began reaching, and turned on a different one. The subjects therefore had to shift their hand movement to press the correct button.

Less than a tenth of a second after the light switched, though, the scientists zapped the subjects, instantly blinding them. With so little time between the switch of lights and the zap, the subjects still thought the center light was on. Yet a significant number of them moved their hand away from the center button and shifted it to the correct one. Their inner zombie didn't need any awareness in order to perceive the change and alter the command it sent to the hand.

In the Danish experiment, the subjects were at least aware of their goal, even if they didn't know how they were achieving it. Other experiments show that our unconscious mind can fully act like a conscious self. Take a recent experiment in which French and English scientists had volunteers play a simple game while undergoing a brain scan. The subjects held a handgrip while watching a computer screen. They were told to squeeze the handgrip whenever they saw a picture of money on the screen. The more they squeezed, the more money they would win.