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Daniel L Adams, Jonathan C Horton; Cortical columns without a function. Journal of Vision 2003;3(9):108. doi: 10.1167/3.9.108.
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In many higher mammals, geniculate inputs to striate cortex serving the left and right eye are segregated into stripes within layer 4 known as ocular dominance columns. These columns can be labeled by processing the cortex for cytochrome oxidase (CO) activity after enucleation of one eye. Because CO levels reflect physiological activity, loss of staining occurs in the columns formerly driven by the missing eye.
For many years, the squirrel monkey was regarded as an anomaly among primates because it was shown repeatedly to lack ocular dominance columns. We visualized the column patterns of 12 normal squirrel monkeys and found a huge range of ocular dominance column periodicity and segregation. At one extreme, columns were large and sharply segregated, resembling those found in macaques and humans. At the other extreme, they were rudimentary and almost entirely absent. In some cases, columns were well defined in some portions of striate cortex, yet absent elsewhere.
It it natural to suppose that ocular dominance columns are required for some aspect of vision, such as stereopsis. Squirrel monkeys, however, have excellent stereopsis. One might propose that a subset of squirrel monkeys, namely, those with weak columns, has poor stereopsis. This possibility should be examined, but it is worth pointing out that columns were virtually absent in 4/12 animals. It seems unlikely that a third of the members of a primate species harbors an innate deficiency in stereopsis, or any other visual function vital for survival. Monkeys with regional expression of columns provided the most compelling evidence against a functional role for ocular dominance columns. It is difficult to conceive of a visual faculty that has a similar distribution across the visual field. These findings lead us inexorably to the conclusion that ocular dominance columns have no functional significance, at least in the squirrel monkey.
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