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Read more: 鈥�Consciousness: The what, why and how鈥�

Liar, liar

Why did you pick that outfit to wear this morning? What made you do your to-do list in that order today? In fact, how did you even end up in that job? You may think you know the reasons, but they could be a work of fiction.

That bizarre conclusion has emerged from studies of people who have had an extreme form of brain surgery 鈥� the complete severing of the thick bundle of nerves connecting the two hemispheres of the brain 鈥� in an attempt to cure their epilepsy.

Such people usually seem fine, but tasks that test cross-talk between the hemispheres can catch them out. In one test, people had different images shown to each eye, and had to point to a similar image with the hand on the same side as the eye.

When one person saw a snow scene with his left eye, he chose a picture of a snow shovel with his left hand. But when asked to explain his choice, he had a problem. His left eye and hand鈥檚 actions were under the control of his right brain, as each brain hemisphere controls the opposite side of the body. But language is controlled by the left brain, which could not access the snowy image 鈥渟een鈥� by the right brain. So the subject invented a reason that had nothing to do with snow: the shovel was for cleaning out a chicken coup, he said, as a chicken was the last image seen by his left brain.

Such findings have led to the 鈥渋nterpretive brain鈥� theory, which says that the brain makes up narratives about our actions to help us make sense of the world. Any of us can be tempted into this sort of confabulation. In one study, people who have never had brain surgery were told to choose a picture from a selection, then tricked into thinking they had picked another. When asked for their reasoning, their explanations were convincing 鈥� and yet had to be entirely imaginary. Who knows how often our consciousness plays these sorts of tricks on us? Clare Wilson

The twilight zone

Fancy experiencing an altered state of consciousness without resorting to hallucinogenic drugs? Easy. We slip into such a state every night when we sleep, although it鈥檚 hard to appreciate it at the time because we are, well, unconscious.

But try paying closer attention to the half-way stage as you drop off, known as hypnagogia. 鈥淚f you are a good observer, you will notice that those spots have a hallucinoid quality to them,鈥� says Tore Nielsen, a sleep researcher at Montreal鈥檚 Sacred Heart Hospital in Canada.

We don鈥檛 know what causes hypnagogia but one theory is that some parts of the brain are falling asleep ahead of the rest. 鈥淚t鈥檚 known that different parts of the brain tune out at different times,鈥� says Nielsen.

Hypnagogia can inspire creativity. Chemist Friedrich August Kekul茅 had his insight about the ring structure of benzene while half-asleep. Then there was the surrealist Salvador Dali, who tuned in to his creativity by letting himself drop off while suspending a spoon over a metal plate. As he fell asleep, the spoon would crash down, jerking him awake while the dream images were still fresh in his mind.

Hypnagogia is not all fun though. It can sometimes trigger one terrifying kind of sleep paralysis, when the nerve inhibition that normally accompanies our dreams kicks in before someone is fully asleep. 鈥淗ypnagogia is largely an uncharted domain,鈥� says Nielsen. 鈥淲e are still developing tools for navigating it.鈥�

Nielsen鈥檚 approach is to track electrical activity in people鈥檚 brains using EEG while they try to take a nap, under instructions to press a button whenever hypnagogia strikes. 鈥淪ometimes you鈥檒l have these half-formed hallucinatory images and you鈥檙e not quite sure whether to call it a dream image. Then you think: 鈥楳aybe it was but now it鈥檚 too late鈥�,鈥� he says. 鈥淚t鈥檚 quite a process to teach yourself to identify these ultra-brief images.鈥� Liz Else

Out of hand

In the 1960s film Dr Strangelove, the lead character had a bizarre affliction. His right arm seemingly had a mind of its own. Such a condition really does exist, although it is vanishingly rare.

People with so-called anarchic hand syndrome find that their affected limb reaches out and grabs things they have no wish to pick up. They might try restraining it with their other hand, and if that doesn鈥檛 work, 鈥渢hey sometimes come to the surgery with their hand tied up鈥�, says Sergio Della Sala, a neuroscientist at the University of Edinburgh, UK, who studies the condition.

The cause is injury to the brain, usually in a region known as the supplementary motor area (SMA). Work on monkeys has shown that another part of the brain, the premotor cortex, generates some of our actions unconsciously in response to things we see around us. The SMA then kicks in to allow the movement or stop it, but damage to the SMA can wreck this control 鈥� hence the anarchic hand, acting on every visual cue.

A few people are unfortunate enough to have damage to the SMA on both sides of the brain, and experience both hands acting outside their control. They are at the mercy of environmental triggers, says Della Sala.

The system sounds like the very opposite of free will 鈥� Della Sala calls it 鈥渇ree won鈥檛鈥�. The findings suggest that, while it feels like our actions are always under our conscious control, in fact there is a lot of unconscious decision-making going on too.

If that sounds implausible, have you ever been driving somewhere on a day off and found yourself heading towards the office the moment you hit part of your normal route to work? That鈥檚 your premotor cortex responding to an environmental cue right there. Clare Wilson