Intracortical connections are not required for oscillatory activity in the visual cortex

Citation Info

Geoffrey M. Ghose and Ralph D. Freeman
Intracortical connections are not required for oscillatory activity in the visual cortex.
Visual Neuroscience, 14: 1192+ (963R-979R), 1997
[There are two versions. Please get Vol. 14, No. 6: pp. 1192+ in the Nov/Dec 1997 issue.]

Key Words: LGN, visual cortex, synchrony, synchronization, oscillation, geniculocortical integration, discharge statistics, coding

Erratum: Unfortunately, there are several serious typesetting errors in equations and their descriptions in the article in the Sep/Oct 1997 issue. The journal has reprinted the corrected version of the article in its entirety in Nov/Dec 1997 issue (pp. 1192+). Please make sure to get the later version.

52 text pages + 8 figures, accepted for publication: Feb. 17, 1997

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Abstract

Synchronized oscillatory discharge in the visual cortex has been proposed to underlie the linking of retinotopically disparate features into perceptually coherent objects. These proposals have largely relied on the premise that the oscillations arise from intracortical circuitry. However, strong oscillations within both the retina and the LGN have been reported recently. In order to evaluate the possibility that cortical oscillations arise from peripheral pathways, we have developed two plausible models of single cell oscillatory discharge that specifically exclude intracortical networks.

In the first model, cortical oscillatory discharge near 50 Hz in frequency arises from the integration of signals from strongly oscillatory cells within the lateral geniculate nucleus (LGN). The model also predicts the incidence of 50 Hz oscillatory cells within the cortex. Oscillatory discharge around 30 Hz is explained in a second model by the presence of intrinsically oscillatory cells within cortical layer 5. Both models generate spike trains whose power spectra and mean firing rates are in close agreement with experimental observations of simple and complex cells.

Considered together, the two models can largely account for the nature and incidence of oscillatory discharge in the cat's visual cortex. The validity of these models is consistent with the possibility that oscillations are generated independently of intracortical interactions. Because these models rely on intrinsic stimulus-independent oscillators within the retina and cortex, the results further suggest that oscillatory activity within the cortex is not necessarily associated with the processing of high-order visual information.

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