An 16 month-old human child is brought to a room by his mother, and in the room is a large mirror propped-up on the floor. The mirror is slightly taller than the child and made of a flexible plastic so it won't shatter. The mother pretends to wipe the child's nose with a kleenex, and in doing so surreptitiously places a black paper dot on the child's cheek. It's so light and soft that the boy can't feel it, but it sticks there with a little bit of adhesive. Then she puts her son down to let him amble around the room, discover the mirror and explore his own reflection. He looks delighted with the reflection and stares at it for a few moments. Wobbling unsteadily on his short legs, he smiles and sticks his tongue out and leans against the mirror, then turns around and looks back at his mother with a silly grin.

 Another experiment is conducted with a little girl, only 22 months old. Her mother does the same thing as the last, pretending to wipe her daughter's nose and placing the small sticky dot on her cheek. This time, when the infant wanders over to the mirror and looks at her own reflection, she immediately reaches up and touches the dot on her cheek, not on the reflection.

 Sometime between 18 and 24 months, humans become self aware. They realize that the reflection in the mirror is the same body that they feel they're presently in, that the image is them. And this "mirror test" has been conducted not just with thousands of human children, but hundreds of different animal species as well. As far as we know now, only chimpanzees, orang-outans and humans display strong evidence of self awareness. Without this awareness we aren't conscious as we know it.

 In another experiment, adult subjects volunteered to have their brain stimulated by intense and focused magnetic fields while they wore a skull-cap embedded with sensors. The sensors detected what parts of the brain were active, and the wand wielded by the scientist delivered magnetic pulses to excite specific, targeted clusters of neurons. The wand looks like the end of a big door key, with two loops of wire wound around an iron core. When current runs through the "key" they create magnetic fields, and the current is pulsed several times per second to tickle the brain's neurons into activity. 

 When the magnetic field was applied to a focused part of the brain, it excited those neurons into activity that ricocheted across the brain, triggering other clusters of brain cells into activity even though they weren't targeted. The scientist then invited the volunteer to lay down on a comfortable bed, relax, close their eyes and drift off to sleep naturally, and after they were asleep they repeated the same experiment. This time there were no ricochets of activity, just one cluster was stimulated at a time, and it didn't trigger activity anywhere else. Why was this? Why, when we are awake and aware does activity in one part of the brain dart around and stimulate others, but when asleep be confined?
 The scientists concluded that what makes consciousness come to life is the communication between the intensively interlinked parts of the brain. We're "awake" and "aware" when all the parts of the brain are responding to the activity of others. The very definition of sleep or unconsciousness is when that behavior temporarily shuts down. When we blank-out every night, dissolve into dream-world and lose our sense of time, is simply when the brain shuts down the interstate highways and expressways that carry impulses from one neuronal city to another. Each city could still be active (and when we sleep, your brain is still very active), but the consciousness--the "me" part of us--disappears until we wake up.

 Lets visit two more experiments. Now every experiment I'm talking about here has been designed to find out where consciousness happens and what consciousness actually is, and in a moment I'll tie the results together in a single explanation. 

 In the first of these two experiments a patient with severe epilepsy had to undergo radical surgery to cut apart the two hemispheres of the brain, having a surgeon's knife sever a cluster of nerves called the Corpus Callosum. Each hemisphere of the brain is capable of fostering an independent mind, complete with its own self-aware consciousness, and the Corpus Callosum synchronizes the two to create the illusion of one person's mind. And the person who wakes up after the surgery appears to be the same one who went under anesthesia before it, because he has the same personality, answers to the same name, greets his wife and family with the same smile, and appears to be the same "them" to everyone who knows him. But something is amiss.

 The disconnection isn't clear to the casual observer, but disturbingly there are only a few simple tests that reveal not one, but two people living in the same skull. The second inhabitant is revealed by exploiting the division of the body to each half of the brain. The right hemisphere controls the left side of the body and receives all the stimulus from it. The left hemisphere controls the right side of the body, so a pinprick to your right hand will get fed to the left side of your brain to feel it. So what if you covered the right-eye with a blindfold and showed a picture or words to the left eye? The right hemisphere--isolated by a surgeon's scalpel--will be the only part of the brain that sees it. And it'll respond to the oblivion of the left hemisphere.

 The patients who undergo this surgery seem to come out with the left hemisphere dominant, and the right hemisphere submissive to its control over the body. Basic coordination such as walking and eating with a knife-and-fork get coordinated lower in the spinal cord, but the two personalities in the skull go off on their own independent way--no longer kept in sync with the cluster of nerves that used to connect them. 

 So the scientist covers up the right eye and then holds up a sign that says "WALK ACROSS THE ROOM". The patient stands up and walks across the room, but after getting there the scientist stops him and asks, "Why did you just walk across the room?" The patient speaks, and because the left brain is dominant--controlling the tongue--he says "To get a can of soda."

 The left brain's view of the world--through the right eye--was blinded. But since the body it inhabits suddenly got up and started walking across the room it was forced to figure out why. It used its powers of prediction and detective work, all the skills we've learned when growing up to figure out how the world and things really work, and it fabricated an explanation from whole cloth. Completely sensible, completely plausible, and wrong. 

 The clincher is that this cocky left hemisphere believed its own imagination, as if it was the literal truth. It just made something up to explain behavior it couldn't explain, and then believed it. Questioned further, the patient remains adamant his flawed belief.

 And so we come to the last experiment, the one that ought to make you really think. When we chose to act--such as to pick strawberry ice-cream rather than vanilla, or to press button A instead of button B--our brain cells generate an action potential that can be measured by a sensor or an MRI machine. The experiment, then, put a normal healthy adult in an MRI machine with two buttons to press, and he was invited to press either one at random. Either button, whichever he wanted, whenever he wanted. The scientists watched the screens of the MRI machine and saw what his brain was doing as it made up his mind which button to press, and with unnerving accuracy, the scientists--or specifically the computer they programmed--predicted it up to 6 seconds before the volunteer was even aware of it himself.

 Part of the volunteer's brain made a decision, carried it out six seconds later, and the consciousness of that volunteer didn't believe he had made the decision until six seconds after he had. Like with the epilepsy sufferer who underwent surgery to cut his mind in half, and later displayed complete faith in the interpretation of a stranger's actions, a normal and healthy person shows the same behavior. Not in the actions of a part of his brain that he can't access, but in a cluster of neurons that is just as well connected as the rest.

 The consciousness that we feel is "us", the "me" we each feel, the internal self-aware narrative of our own lives, is a spectator. It's a product of what small clusters of specialized brain cells have already done, synchronized and orchestrated into a personality that believes its in control. But it isn't in control, it only summarizes and informs the rest of our brain like a daily newsletter. It serves a purpose, of course. It guides and influences what we do, but what it believes is a fabrication. 

 The mapping of the brain began more than a hundred years ago with the now-discredited science of phrenology. Phrenology, although flawed, did at least have the insight that different parts of the brain have special purposes. Phrenology was only broken because it held that behavior could be predicted by the lumps on your skull, where a lump in one place predicted criminal behavior or altruism or compassion. One phrenologist of note was Paul Broca, a doctor with a patient who suffered from aphasia--the inability to speak. This patient could write what they wanted to say, given a pen and paper, but couldn't control their tongue and vocal cords to speak it. After she died, Broca dissected her brain and discovered a lesion on the left hemisphere and began to theorize that this lesion--this brain damage--occurred on the part of the brain that was in control of speech. "Broca's Area" was the first physical evidence that different parts of the brain were specialized, and that damage to these areas would compromise function they performed--in this case, speech.

 More evidence would arrive. A railroad construction worker named Phinneas Gage, for example, would become the most famous patient in the world of neurophysiology after a tamping rod--used to pack explosives for breaking up rock in a hillside that a railway line was to run through--was blown through his brain by an accidental premature detonation. Phinneas survived the accident, but his personality was irreversibly changed. "Gage was no longer Gage" his friends would say, for he became impatient and ill tempered after the accident. The tamping rod had shot through a part of his brain called the frontal cortex, which researchers have come to conclude has an effect on the personality and how one predicts the outcome of our actions. The damage made him unable to sense the effect of his actions, robbing him of his conscience, turning him into an asshole.

 We've been learning, accident by accident, experiment by experiment, that consciousness is a secondary function of the brain. It isn't necessary for life, but it may be an advantage for evolution. The "us" that we believe we are, the ghost in the machine, the personality that we think is ourselves, is a convenience for the rest of our brain and our body. "We" are backseat drivers, and what's in control is just another animal.