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The cheerful centenarian, once a famous coach to stars of the music world, now sat at her piano playing an endless loop of music that ended at the limit of her short-term memory. She told me that lately she had been enjoying the delightful marching band of vividly colorful insects visible in parade around the baseboard moldings that encircled the piano room. She was suffering, or rather not suffering, from Lewy body dementia, a Parkinson's syndrome that features pleasant hallucinations. But why do such hallucinations, and others from medications such as amantadine used to treat Parkinson's, often appear along the baseboard of the room? This is possibly because the non-foveal peripheral vision is great at detecting or imagining motion but isn't very accurate, and allows such creative projections. Sacks devotes his first chapter to Charles Bonnet syndrome in the visually impaired, either from ocular or visual system disease, and it made me think about such cases. What may be “seen” in blindness ranges from colors and geometric forms to battlements and bridge numbers or even performances on a stage. But neural degeneration in my seeing patient was only part of the derivation of her hallucinations, to which her love of music was added.
Throughout Sacks's latest collection of wonderful disorders, the personally dynamic hovers at the edge of explanation, and in his announced paucity of discussion of “the vast and fascinating realm of dreams”—Freud's perception in reverse—Sacks reveals his neurologist's preference for neural gadgetry. This is fitting for the world's most notable neurologist since Freud, who has had a film and a modern dance made from his book Awakenings—and as usual, he has found plenty of neurophysiological mechanisms to describe. We are all the more edified, and prevented by our edification from a host of diagnostic errors from overly dynamic inferences about symptoms. For example, the projected form of benign paroxysmal positional vertigo was experienced