Back in 2007, scientists reported that a French man in his mid-40s had walked into a clinic complaining of a pain in his leg. As a child, he’d had this same problem as a result of the ventricles in his brain filling with cerebrospinal fluid, so the doctors decided to scan his brain to see if this was again causing his limb-related lamentations. To their astonishment, they found that his ventricles had become so swollen with fluid that they’d replaced virtually his entire brain, leaving just a thin cortical layer of neurons.

Yet miraculously, the man was not only fully conscious, but lived a rich and unhindered life, working as a civil servant and living with his wife and two kids, blissfully unaware of the gaping hole in his brain. His ability to function without so many of the key brain regions previously considered vital for consciousness raises some major questions about existing theories regarding how the brain works and the mechanisms underlying our awareness.

For example, neuroscientists have often asserted that a brain region called the thalamus, which relays sensory signals to the cerebral cortex, is indispensable for consciousness. This is because research has indicated that damage to the thalamus often causes people to fall into a coma, while one team of scientists were even able to manually “switch off” an epileptic patient’s consciousness by electrically stimulating this brain region.

Similarly, researchers have shown that it is possible to cause people to lose consciousness by using electrodes to manipulate the activity of a brain region called the claustrum, which receives input from a wide variety of brain areas and communicates extensively with the thalamus.

Image: A brain region called the thalamus has been shown to be vital for consciousness to exist. Tefi/Shutterstock