Wednesday, June 25, 2008

Neuroscience: Making sense of uncontrollable itching

In the New Yorker's "Annals of Medicine", Atul Gawande writes about a woman who was plagued with such terrible (and unexplained) itching that she would unconsciously scratch in her sleep until

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.

Yes, pretty gross. But she, and other people like her, have helped pave the way for an understanding of the actual way in which itches - not a form of pain, as previously believed, but a separate nervous system - are experienced:
Unlike, say, the nerve fibres for pain, each of which covers a millimetre-size territory, a single itch fibre can pick up an itchy sensation more than three inches away. The fibres also turned out to have extraordinarily low conduction speeds, which explained why itchiness is so slow to build and so slow to subside.
Anyway, if you scratch itches and don't seem able to help yourself, take heart! You are not crazy or merely uncooperative ... your itch has a glitch. And neuroscientists are beginning to get some idea how to really help.

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