Saturday, July 5, 2008

Brain Scratchingly Awesome

The New Yorker recently ran an installment of its "Annals of Medicine" series describing the neuroscience and philosophy behind the itch sensation. The first half of the article (roughly) deals with how the itch sensation is generated, using a case study of a woman they call "M." as an example. M., apparently, suffered from shingles as a result of an active HIV infection, and after they subsided, began experiencing a persistent and maddening itch in the scalp. One passage is particularly grisly, so (of course) I'm including it here. Snip:
For M., certainly, it did: the itching was so torturous, and the area so numb, that her scratching began to go through the skin. At a later office visit, her doctor found a silver-dollar-size patch of scalp where skin had been replaced by scab. M. tried bandaging her head, wearing caps to bed. But her fingernails would always find a way to her flesh, especially while she slept.

One morning, after she was awakened by her bedside alarm, she sat up and, she recalled, “this fluid came down my face, this greenish liquid.” She pressed a square of gauze to her head and went to see her doctor again. M. showed the doctor the fluid on the dressing. The doctor looked closely at the wound. She shined a light on it and in M.’s eyes. Then she walked out of the room and called an ambulance. Only in the Emergency Department at Massachusetts General Hospital, after the doctors started swarming, and one told her she needed surgery now, did M. learn what had happened. She had scratched through her skull during the night—and all the way into her brain.

The second half of the article discusses the philosophical implications of M.'s case (and of itching in general), discussing naive realism, Berkeley's idealism, active perception, and phantom limb cases. It's well written (as one might expect in the New Yorker), and very, very interesting.

EDIT: Some of you might be wondering, as I was, how it is possible to scratch through one's own skull over the course of a single night. It turns out that, because of her HIV, M.'s wound became infected, and that turned into osteomyelitis, which softened the bone to the point that this was possible. The more you know.

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