Spacing of cytochrome oxidase blobs in visual cortex of normal and strabismic monkeys

Some models of visual cortical development are based on the assumption thatthe tangential organization of V1 is not determined prior to visualexperience. In these models, correlated binocular activity is a key elementin the formation of visual cortical columns, and when the degree ofinterocular correlation is reduced the models predict an increase in columnspacing. To examine this prediction we measured the spacing of columns, asdefined by cytochrome oxidase (CO) blobs, in the visual cortex of monkeyswhose binocular vision was either normal or disrupted by a strabismus. Thespatial distribution of blobs was examined in seven normal and fivestrabismic macaques. Tangential sections through the upper layers of thevisual cortex were stained to reveal the two-dimensional (2D) pattern of COblobs. Each blob was localized and their center-to-center spacing, packingarrangement and density were calculated using 2D nearest-neighbor spatialanalyses. The mean center-to-center spacing of blobs (590 microm fornormally reared and 598 microm for strabismic macaques) and the meandensity of blobs (3.67 blobs/mm2 for normally reared and 3.45 blobs/mm2 forstrabismic macaques) were not significantly different. In addition, the 2Dpacking arrangement of the blobs was not affected by strabismus. While itis clear that neural activity plays a key role in the elaboration andrefinement of ocular dominance cortical modules, we conclude that it doesnot determine the spatial period of the pattern of CO blobs. This suggeststhat aspects of the neural circuitry underlying the columnar architectureof the visual cortex are established prenatally and its fundamentalperiodicity is not modifiable by experience.