Calcium ions have a pivotal role in many neuronal activities1, but little is known about their involvement in the cortical processing of visual information2. Using immunohistochemical methods, we have now detected a calcium-binding protein, calbindin-D-28K (ref. 3, calbindin), which may confer on certain compartments of cortical area 17 the ability to modulate Ca2+ metabolism. Thus, calbindin occurs in the primate striate cortex in a pattern almost complementary to that displaying strong cytochrome c-oxidase activity. From this and other observations, we deduce that the distribution of calbindin-immunoreactive sites corresponds mainly to extra-geniculocortical connections of the primary visual cortex. This implies that the geniculocortical and extra-geniculocortical compartments of area 17 differ in an intracellular system for Ca2+ homeostasis.
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