I have always admired Sacks's writing about his patients because I feel that I am reading about people rather than cases. I am a great admirer of Sacks's early books like An Anthropologist on Mars and The Man Who Mistook His Wife for a Hat, both are less continuous narratives than Hallucinations or Sacks's recent Musicophilia and The Mind's Eye. Rather than thematic in nature, these earlier books are simply collections of essays on human beings whose strange neurologic cases make them fascinating, but who otherwise have little or no relation to each other. I found some of the material included in Hallucinations had to stretch to be subsumed under the book's theme. While I found most of the material interesting, an episodically constructed book might have been a more natural and satisfying form.
On more than one occasion in this book (and his last, The Mind's Eye) Sacks becomes his own subject. In this case, he writes frankly of his experimentation with hallucinogenic drugs, a piece that appeared in The New Yorker last year, and of a serious hiking accident during which Sacks says that a voice commanded him to keep going.
I am always impressed by the historical sources Sacks cites. They immediately make me want to visit the library. Jackson's original papers on epilepsy and aphasias, are cited in Hallucinations. Perhaps this is not as enticing to the average lay-reader, but for a neuroscientist, these are the golden oldies. Jacksonian seizures were named for John Hughlings Jackson.
Hallucinations makes colorfully clear that the mechanisms in the brain that eventuate patients' perceptions in the absence of external stimulation can be diverse. The light patterns that are experienced in the aura prior to migraine might be thought of as electrical disturbances like a wave passing across the visual parts of the brain. Whereas the hallucinations reported around near death experiences such as a floating above one's own body may occur due to stimulation of the right angular gyrus, one of several brain regions implicated in a circuit that according to Sacks mediates body image and vestibular sensations. The vision of a dark tunnel with light at the end may be the result of decreased circulation to the retina, which narrows the visual fields.
The most remarkable of the cases Sacks writes of in Hallucinations was that of an 86-year-old English man who already had glaucoma and macular generation, but when a stroke compromises his right occipital lobe he loses vision completely in his left visual field. What is most interesting is that he is not aware of his loss
...his brain appears to fill in the missing parts. Interestingly, though, his visual hallucination/filling in always seem to be context-sensitive or consistent. In other words, if he is walking in a rural setting, he can be aware of bushes and trees or distant building in his left visual field, which when he turns to engage his right side, he discovers are not really there. The hallucination do, however, seem to be filled in seamlessly with his ordinary vision. If he is at his kitchen bench, he "sees" the entire bench, even to the extent of perceiving a certain bowl or plate within the left side of his vision - but which on turning disappear, because they were never really there. Yet he definitely sees a whole bench, with no clear separation between parts composed of hallucination and true perception.The human brain is a remarkable country and it is always enjoyable to travel there with Oliver Sacks as your guide.