Optical Mapping of Cortical Activity

Neuroscientists have long wanted to "see" events inside the brain. The main objective of their research, after all, is to deduce relevant response properties in various parts of the brain and explore their organizations. The ability to "see" these organizations directly— to visualize regions activated by specific stimuli—has an obvious advantage. This is especially apparent in the mapping of neocortex, where many important organizations occur tangentially in a plane parallel to the surface. Striate cortex (a.k.a., primary visual cortex, area 17, or V1) offers a useful example. Located in the occipital lobe, along with other visual areas, this is the first area (in primates, at least) to receive input directly from the lateral geniculate nucleus (LGN). To a first approximation, this input is mapped retinotopically; neighboring parts of the visual field are represented in neighboring parts of cortex. But there are at least two additional properties—orientation selectivity and ocular dominance—that are mapped laterally as well.

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