Imagine for a moment that you take your car to a mechanic, and find out that s/he has never actually taken apart a fully functional car engine. The only experience they had was in tinkering with broken engines, the machines the owners had complained about, or motors they had found for themselves, left unrecoverable in some junkyard. It seems strange, doesn't it, to imagine a world in which these mechanics would be considered acceptable - yet in the world of neurology, it seems that is the usual case. It is rare that a doctor has deep experience with normal physiology. Too often they learn only from the extreme outer edges of the bell curve, where the case history is detailed but strange. Oliver Sachs has this difficulty too, yet somehow he extricates some profound insights about how the brain works even with - or sometimes because of - his access to profoundly neurologically injured or impaired persons.
The most interesting information I got from the book is that the brain has actual physical connections running retrograde from sense organs to neurological processing centers. In other words, sense organs do not have a one-way corridor of input to the brain. The brain can signal back to the sense organs to dampen or sharpen input, or to fill in gaps in an input stream. Taken to an extreme of sensory deprivation, these channels from the brain can manufacture sensory input en toto and with such authenticity that the input channels perceive the sense input as being external. In this way in particular sound hallucinations can occur. Sachs then is able to argue convincingly that these thoughts we experience in relation to sense stimulus are triggered based on physical neurological reactions, and not from some mystical or ethereal process.
Individuals who have experienced brain trauma (eg a concussion or injury) often experience such hallucinations. In fact, this explains an incident from my own childhood about which I have argued with my mother over time. When I was approximately 5 years old, I experienced a concussion. Fortunately, family friends who were nurses along with my mother took turns monitoring me and checking in with my pediatrician so that I did not have to be hospitalized. During that time, and to this day, I can distinctly recall that a girl who lived in the neighborhood (Ludy Trevino, if you're out there in the blogsophere say 'hey!') played her violin for me. I didn't see her, but can still vividly recall the music. My mother has always insisted that this friend did not play for me then, especially since it was overnight and the girl herself was not at our home but much more likely sleeping in her own bed at her home. After reading Sacks' accounts, I am convinced that it is much more likely that I was experiencing musical hallucinations brought on my the head trauma. I've never had any other hallucinations since, and the veracity of the musical experience was striking - to this day, I can remember it as though it happened.
One very interesting segment of the book concerns earworms - those viral musical fragments which can occupy one's mental space and take some mental floss to remove. Sacks discusses this in a video available on Youtube:
And, also on this note (don't mind the pun), I've heard that there will be an excellent installation art exhibit at the Pasadena Museum of California Art on Earworms . Catch that for yourself for more on this wacky phenomenon.
The publisher offers an audio excerpt from Musicophilia:
Check out Oliver Sacks's website for more details.