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Math Explains Hallucinations
By: Wynne Parry
Issue date: 12/3/01 Section: News
While in drug-induced states, a mathematician recorded the funnels, cobwebs, spirals and honeycomb shapes he saw.
These hallucinations are universal humans ones. They are false images teased from the brain by flickering light, certain anesthetics, waking and falling asleep and drugs.
They were nothing new when the mathematician made his record in the '60s. One of the forms he recorded was a cobweb resembling an image found on a petroglyph.
These re-occurring images say something about the human brain, according to Paul Bressloff, a U math professor.
Normally, visual perception begins when the eyes receive light, which they turn to electrical signals. The signals pass to the rear of the brain, the primary visual cortex, for the first stage of processing.
Because the blind also hallucinate and because the images remain stable even when the eye is moving, hallucinations must be generated without input from the eyes, Bressloff and his colleagues theorized.
Hallucinogens act directly on the brain, triggering the release of chemicals that affect the brain's state. When the brain is in an altered state, the visual cortex generates hallucinations.
And because the imagery is universal, hallucinations may be linked to the architecture of the visual cortex.
Bressloff and others investigated by developing a mathematical model.
Mathematical symmetry underlies the architecture of the visual cortex and determines the cells' modes of firing. There is similar symmetry behind other phenomena in natureâ??markings on the coats of animals and water currents generated by heat flow.
The presence of symmetry in the brain was the foundation for the study.
Within the visual cortex, particular cells correspond with small areas of the field of vision.
Each cell is also attuned to particular properties of the light. So in the visual cortex, an object is broken up into little edges with different orientationsâ??a bit like a line drawing, Bressloff said.
The pieces of information the cells pick up is assembled by the brain later on.
When stimulated by light, cells packed together in a small area tend to talk to one another. At longer distances, only cells that respond to similar properties communicate with each other.
By changing the brain's state, hallucinogens amplify natural patterns of activity in the cells. They cause the cells to fire off signals and produce the patterns that dance before the eyes.
Bressloff and his colleagues mathematically modeled this situation. When they mapped the hallucinations onto the visual cortex, funnels, spirals and cobwebs became grids of lines, dots and small bars, respectively.
Many aspects of hallucinations still remain to be explored. Some hallucinations also incorporate elements such as depth or color.
Jack Cowan of the University of Chicago, Martin Golubitsky of the University of Houston, Peter Thomas of the Salk Institute for Biological Studies and Matthew Wiener from the National Institutes of Health also participated in the research.
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