But here is the punchline: patterns of hallucinations reflect normal modes of the neurons in the visual cortex. By "normal modes" we mean the characteristic patterns of vibration, just as for a violin string or the head of a drum. The idea is that a drug such as LSD can alter the ground state of the visual cortex, so that it becomes excited even in the absence of stimuli. In particular, certain oscillating patterns can appear spontaneously. Generally these would take the form of different configurations of straight lines in the cortex itself; however, due to the distortion in the map from our visual field to the brain, these appear to us as spirals, tunnels, and so on. Indeed, Cowan and collaborators have shown that these normal modes can successfully account for all of the basic forms of hallucination classified by Kluever decades ago.Take time to read the comments, too. In the comments there's a comparison to other mathematical models of the brain which do not fit as well as these wave functions.

## Wednesday, February 09, 2005

### Preposterous Universe: Hallucinatory neurophysics

U Chi Physicist Sean Carroll describes this recent work in mathematical neurophysics. Essentially, describing in mathematical terms/wave equations the patterns of hallucinations.

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