Neurologists may have found a control switch for consciousness.
A case study by Koubeissi and colleagues, published earlier this year in Epilepsy and Behaviour, has revealed that a brain region with previously unknown function could be one of the master controls for our conscious experience. The circumstances of the experiment were even more surprising than the result itself: the authors originally had no intention of studying consciousness, but were instead attempting to help a patient with epilepsy.
The patient in question suffered from epileptic seizures that no longer responded to any known treatment. First, she had electrodes implanted within several areas of the brain, and then Koubessi et al. applied a weak electrical current to these electrodes in an effort to find the brain region causing her seizures. (This is termed deep brain stimulation, and is used to treat the symptoms of Parkinson’s disease as well as for mapping areas of the brain.) All proceeded normally – until they applied current to the electrode next to an area called the claustrum, when the patient gradually lost consciousness. As soon as the current stopped, she started to wake up, much like coming round from an extremely short-acting anaesthetic.
The claustrum itself is an odd brain region with enigmatic function. It is an irregular sheet-like structure located under the inner surface of the cortex; neurons within the claustrum are also extremely well-connected, being able to send signals to, and receive input from, practically all areas in the cortex. Some researchers have previously speculated that the claustrum’s connections could help it co-ordinate the cortical regions that process different aspects of conscious experience. For example, some groups of neurons might encode information about shape and colour, another group, taste or smell, but presumably we need some way to unify this information into the experience ‘I’m drinking a tasty pink gin from a teacup’. Apart from some experiments in animal models, though, there have been very few functional studies of the claustrum’s role in conscious awareness – until now.
Even so, the 2014 results are not necessarily as conclusive as they sound. First, epilepsy is characterised by abnormal electrical activity, and many theories of consciousness suggest a role for tightly regulated neuronal firing, so any conclusions drawn from a case study using an epileptic patient need to be interpreted with care. Also, the patient was actually missing part of her brain: several years before the surgery described in the paper, her left hippocampus had been removed in a previous attempt to control her seizures. (Surgeries like this are often effective in people who have seizures originating in discrete brain regions, and the patient’s seizures did indeed stop for a while.) To confirm the link between consciousness and the claustrum, much more study is needed in brains with normal function.
The authors suggest that their work could have further applications for treating epilepsy. Since consciousness is disrupted during a seizure, applying a different electrical stimulus to the claustrum could prevent epileptic patients from ‘blacking out’. Artificially inducing unconsciousness could also plausibly help people with sleep disorders, particularly insomnia. (There are already eerily similar scenarios in science fiction and fantasy: in one novel, set during an epidemic of untreatable insomnia, a character has a deep brain electrode that helps her sleep by switching on for 8 hours each night!) Whether induced unconsciousness would have the same physiological and psychological benefits as sleep, however, is uncertain. Our sleep cycle is characterised by movements between different states of brain activity, some of which – such as lucid dreaming – share common features with waking states. We are still a long way from being able to treat insomnia with an electrode – or being able to throw any master switches for consciousness.
– PubMed citation for Koubeissi et al.’s 2014 case study
– Crick and Koch speculate on the function of the claustrum
– Insomnia and deep brain electrodes in science fiction: Black Moon, by Kenneth Calhoun