Watch Oliver Sacks’ 2009 TED Talk on Hallucinations in the Blind

The recently departed neurologist discusses the surreal affliction of Charles Bonnet syndrome.

Aug 31 2015, 9:03pm

The brilliant, soft-spoken neurologist Oliver Sacks passed away yesterday after a protracted battle with ocular melanoma at the age of 82. Sacks was known, among other things, for writing books containing particularly detailed and absorbing case studies of his patients, many of whom suffered from little-understood and relatively uncommon neurological disorders.

In his 2009 TED Talk, Sacks discussed Charles Bonnet syndrome, which affects at least 10 percent of the vision-impaired but is not discussed or diagnosed in proportion to its occurrence.

With Charles Bonnet syndrome, patients who have lost all or most of their eyesight have complex, recurring hallucinations. Faces, cartoons, and geometric patterns are common.

By conducting fMRI experiments on Charles Bonnet patients while they were hallucinating, researchers saw that corresponding parts of the inferior temporal cortex were activated depending on what the patients saw. In fact, there are clusters of cells dedicated to processing different types of images, and the mental discharge of these cells is responsible for the hallucinations.

Sacks talks about meeting an elderly woman who was still mentally sharp, but feared reporting her hallucinations would get her labeled insane—which is the reason Charles Bonnet syndrome goes underreported. In his last book, Hallucinations, Sacks attempted to remove some of the stigma around the idea of "seeing things," as hallucinations have many causes outside the realm of mental illness.