For centuries, both philosophers and scientists have been trying figure out exactly what "consciousness" is, where it comes from, and how it works.
While they haven't now answered all those questions, researchers have located the mechanism deep in the human brain that seems to control it -- an on-off switch for consciousness.
In a new study -- published this week in the journal Epilepsy & Behavior -- neurologist Mohamad Koubeissi of George Washington University recounted how he and his colleagues were able to turn a woman's consciousness off and on by stimulating her claustrum.
The late pioneering neuroscientist Francis Crick and his still-working colleague Christof Koch, a researcher at the Allen Institute for Brain Science, previously pinpointed the claustrum, a thin, sheet-like component deep in the brain, as integral in orchestrating a composite of distinct brain activities -- a combination of thoughts, sensations and emotions that might be defined as "consciousness."
But Koubeissi and his researcher partners are the first to lend credence to the hypothesis via hard evidence.
As the new study explains, when GW researchers zapped a woman's claustrum with high frequency electrical impulses, she subsequently lost consciousness. The claustrum shocks caused -- as researchers explained -- "arrest of volitional behavior, unresponsiveness, and amnesia without negative motor symptoms or mere aphasia."
When shocked, the woman remained open-eyed, but seemingly blank -- staring ahead, unaware of the world around her.
"I would liken it to a car," explained Koubeissi. "A car on the road has many parts that facilitate its movement -- the gas, the transmission, the engine -- but there's only one spot where you turn the key and it all switches on and works together."
"So while consciousness is a complicated process created via many structures and networks -- we may have found the key," added Koubeissi.
"Normally when we look at conscious states we are looking at awake versus sleep, or coma versus vegetative state, or anaesthesia," said Anil Seth, who argues a single case study such as this should be taken with a grain of salt.
Still Seth, who studies consciousness at the University of Sussex, is intrigued by the findings -- especially by the fact that the participant remained awake while she was apparently unconscious.
"So even though it's a single case study, it's potentially quite informative about what's happening when you selectively modulate consciousness alone."
Christof Koch, whose early research enabled the latest revelations, says the search to understand consciousness is essential.
"Ultimately, if we know how consciousness is created and which parts of the brain are involved then we can understand who has it and who doesn't," said Koch. "Do robots have it? Do fetuses? Does a cat or dog or worm? This study is incredibly intriguing but it is one brick in a large edifice of consciousness that we're trying to build."