Thursday, July 14, 2005

Why is Harvey the Rabbit always male?

The BBC has a short segement on auditory verbal hallucinations . Auditory verbal hallucinations are a common symptom of schizophrenia, occuring in about half of all patients. Apparently more than 70% of these patients-- male or female-- report hearing a male voice during hallucinations. The false voices are furthermore likely to be middle-aged and carry derogatory messages. (The Beeb does not include these details, but the article says that the voice is also typically right-localized,external and speaks in a monotone, "like a BBC newsreader.")

A new article in NeuroImage proposes an explanation for the gender bias of these hallucinations. Normal healthy volunteers listening to computer-altered recordings showed different brain activity (by fMRI) in response to male, female, or indeterminate voices. Specifically, perception of a female voice correlated with increased activation of the superior temporal gyrus relative to perception of a male voice. The authors propose then that the brain state corresponding to hearing a (real) male voice is a kind of default, and the easiest for the brain to mimic during hallucinations. They want to go back and test these ideas on schizophrenia patients.

Perception of a female voice yields more complex responses both because of the shape of their larynx gives a more acoustically complex sound and because (English speaking?) women employ more melody while speaking. This makes me think that the authors should evaluate speakers of a tonal language and see whether the difference in brain activation based on speaker's voice would still hold.

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