The precise area the surgeons had zapped included a sliver of tissue known as the claustrum, which is part of a network that supports awareness. Mohamad Koubeissi and his colleagues state that nobody has ever examined the effects of stimulating this specific brain region before, despite this kind of surgical procedure having been performed for decades. Just as geographers still surprise us with reports of having discovered previously unchartered parts of the earth, it takes one aback to hear of unexplored areas of neural terrain.
Intrigued by the woman's response to the stimulation of this specific brain region, the surgeons investigated further. Ten further stimulations, and on every occasion zapping the claustrum had the same effect. By contrast, zapping an area just 2.7mm away did not.
Perhaps the woman was simply paralysed by the electrical stimulation? The effects are more intriguing than that. If given an instruction prior to the stimulation, such as words to utter or movements to make, she continued this for a few seconds after the stimulation began, but then descended into still, unresponsive stupor. It was also striking to observe that as soon as the stimulation ended, the woman regained consciousness. However, she had no memory of the preceding moments during the stimulation period.
The researchers also examined the synchronisation of activity across the brain during the stimulation of the claustrum. They found that it increased synchronisation across the brain, possibly to a debilitating level. If so, this would match the situation observed in epileptic seizures that trigger loss of consciousness.
Caution is required - after all, this is a single case study, and the patient in question was missing part of one hippocampus, removed during earlier treatment for epilepsy. Nonetheless this is an intriguing finding. "... [T]he disruption of consciousness that we herein describe has never been precipitated by electrical stimulation of any other site in the human brain," the researchers said.
Speaking to New Scientist magazine, lead author Koubeissi likened the claustrum to a car's ignition. While both the brain and the car are made up of many functioning parts, "...there's only one spot where you turn the key and it all switches on and works together," he told them. "So while consciousness is a complicated process created by many structures and networks - we may have found the key." If these results can be replicated, the hope is that stimulation of the claustrum may offer a way to treat disorders of consciousness associated with epileptic seizures.
Mohamad Z. Koubeissia, Fabrice Bartolomei, Abdelrahman Beltagy, Fabienne Picard. (2014). Electrical stimulation of a small brain area reversibly disrupts consciousness. Epilepsy & Behavior Volume 37, August 2014, Pages 32–35
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.