“What hallucinations reveal about our minds” by Oliver Sacks
Hallucinations, imagination, dreams — these are forms of “seeing with the brain” rather than with the eyes. Hallucinations, as described by Oliver Sacks, are different than dreams and the imagination because they are meaningless, unrelated to thoughts, emotions, actions, and the person is not in control of what they are perceiving.
Sacks specifically describes Charles Bonnet syndrome, a visual hallucination often experienced by the visually impaired. Affected individuals typically “see” deformed faces, buildings, animals, geometric shapes, even cartoons, which appear and disappear suddenly and seem like a silent movie (Sacks himself claims to experience geometric hallucinations). The images are non-emotional and insignificant to the person experiencing them. This syndrome has been known to science only since the 18th century, but Sacks muses whether ancient art could have been inspired by similar visual hallucinations.
The speaker estimates that 10 percent of visually-impaired people experience Charles Bonnet syndrome, but only one percent are willing to share their experiences for fear of being labeled or diagnosed as “insane” — likewise with hearing-impaired people. It’s commonly thought that hallucinations are a sign of psychosis, but Sacks differentiates true psychotic hallucinations as interactive, usually in a negative way. According to patient.co.uk, the syndrome “is thought to occur in about 10 to 15 percent of patients with moderate visual loss and possibly up to 50 percent of people with severe visual loss.” The goal of Sack’s speech is to raise public and medical awareness of behalf of affected individuals.
So what’s happening in the brain, or as Charles Bonnet himself put it, how is the “theater of the mind” generated by the “machinery of the brain”? Deterioration of the visual capability of the eyes or certain areas of the brain somehow cause neurons in these areas to become excitable and hyperactive, and they begin firing spontaneously. Functional MRIs reveal that geometric patterns are perceived by neurons firing in the primary visual cortex, which perceives edges and patterns, while more elaborate visions, such as faces, are imaged by the fusiform gyrus. In particular, the anterior gyrus perceives teeth and eyes, so when this area is particularly active, people perceive deformed faces. Likewise, buildings, landscapes, and cartoons are all the result of activation in specific parts of the brain. Since the brain is receiving random and fragmented inputs, it is forced to construct a coherent perception. As Sacks concludes, this anomalous occurrence is “valuable for providing insight about how the brain works.”