For the first time, researchers have been able to switch off consciousness in a woman by electrically stimulating a single brain area.
The discovery suggests that a single area - the claustrum - might be integral to combining disparate brain activity into a seamless package of thoughts, sensations and emotions.
Mohamad Koubeissi at the George Washington University in Washington DC and his colleagues said they managed to switch a woman's consciousness off and on by stimulating her claustrum - a thin, sheet-like structure that lies hidden deep inside the brain.
The woman has epilepsy so the team were using deep brain electrodes to record signals from different brain regions to work out where her seizures originate, 'New Scientist' reported.
One electrode was positioned next to the claustrum, an area that had never been stimulated before.
When the team zapped the area with high frequency electrical impulses, the woman lost consciousness. She stopped reading and stared blankly into space, she didn't respond to auditory or visual commands and her breathing slowed.
As soon as the stimulation stopped, she immediately regained consciousness with no memory of the event. The same thing happened every time the area was stimulated during two days of experiments.
To confirm that they were affecting the woman's consciousness rather than just her ability to speak or move, the team asked her to repeat the word "house" or snap her fingers before the stimulation began.
If the stimulation was disrupting a brain region responsible for movement or language she would have stopped moving or talking almost immediately.
Instead, she gradually spoke more quietly or moved less and less until she drifted into unconsciousness. Since there was no sign of epileptic brain activity during or after the stimulation, the team is sure that it wasn't a side effect of a seizure.
Koubeissi said that the results do indeed suggest that the claustrum plays a vital role in triggering conscious experience.
The team also found that the woman's loss of consciousness was associated with increased synchrony of electrical activity, or brainwaves, in the frontal and parietal regions of the brain that participate in conscious awareness.
Although different areas of the brain are thought to synchronise activity to bind different aspects of an experience together, too much synchronisation seems to be bad, researchers said.
The brain can't distinguish one aspect from another, stopping a cohesive experience emerging, they said.
