Day 142: What hallucinations tell us…

As part of his role in a nursing home, neurologist Oliver Sacks was once called to see a lady in her nineties who had been completely blind from macular degeneration for five years and had recently began to see things, which she described as being like a boring movie. Another patient he saw had no issues with her eyes but had a tumour in the visual cortex of her brain; she saw cartoons of Kermit the Frog. The faces in her hallucinations were often deformed and frightened her.
In this talk Sacks discusses Charles Bonnet syndrome, when visually impaired people experience lucid hallucinations. As the visual parts of the brain stop receiving input they become hyperactive, causing the visually impaired to see things. Less than 1% of people getting these hallucinations acknowledge them for fear that they will be seen as crazy. Faces are the most common hallucination; cartoons are the second most common. These relate to different parts of the brain becoming activated (In the 1970s, various brain cells were discovered for recognition of faces, landscapes, etc.)
Sacks himself is blind in one eye and has experienced some geometric hallucinations, surely allowing him to talk about his patients with such empathy. As he tells us, 250 years previously, Charles Bonnet wondered how the theatre of the mind could be generated by the machinery of the brain. Finally with modern science, we’re beginning to understand how this can be done.


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