Disconnecting Consciousness from the External Environment

An very interesting report from a group of French neurosurgeons sheds light on the neural basis of consciousness and dreams. Guillaume Herbet and colleagues describe the case of a 45 year old man in whom electrical stimulation of a particular spot in the brain "induced a dramatic alteration of conscious experience in a highly reproducible manner." The man had brain cancer (a diffuse low-grade glioma of the posterior left hemisphere). During the surgery to remove the tumour, Herbet et al stimulated various points on his brain to map out the areas that were functionally most important. This is a standard procedure to allow surgeons to know which bits they ought to leave intact, where possible. Most of the stimulations didn't do much, but there was a particular point, in the white matter beneath the left posterior cingulate cortex (PCC), where the electrical pulse caused the patient to become unresponsive - to 'zone out', essentially - for a few seconds. This point is marked as "S1" (small blue spot) on these images. The red zone on the left is the area that was eventually removed.