The On, Off Switch of Consciousness | Breakthrough

To map what goes on inside the brain, Muhammad implants tiny electrodes in his patients' skulls. He then sends pulses to these electrodes, gradually increasing the current, sometimes with dramatic results. Recently, he inserted an electrode next to a small region called the claustrum. The claustrum is uniquely connected to other parts of the brain.

When we were doing the mapping, we were surprised to see what the stimulation of the claustrum resulted in. I asked her to read, and I discovered that stimulation of this one electrode, which is in the claustrum, made her stop reading and have no memory of what happened during the stimulation.

When I was 21, my mother died after a decade-long illness. When Muhammad sends a 14 milliamp electric pulse into the claustrum, the patient freezes midsentence. It's as if her conscious mind has been switched off. Cognitively, she is completely impaired—no language function, no memory function, nor responsiveness.

We drove the country road out to her. When the current is reduced, she picks up exactly where she left off. I taught English at a small college in the Bay Area. The findings led some authors to name the claustrum the on-off switch of consciousness, which, based on this case, is actually pretty accurate.