INTRACORTICAL CONNECTIONS ARE NOT REQUIRED FOR OSCILLATORY ACTIVITY IN THE VISUAL-CORTEX

Synchronized oscillatory discharge in the visual cortex has been propo sed 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 lateral ge niculate nucleus (LGN) have been reported recently. To evaluate the po ssibility that cortical oscillations arise from peripheral pathways, w e have developed two plausible models of single cell oscillatory disch arge that specifically exclude intracortical networks. In the first mo del, cortical oscillatory discharge near 50 Hz in frequency arises fro m the integration of signals from strongly oscillatory cells within th e LGN. The model also predicts the incidence of 50-Hz oscillatory cell s within the cortex. Oscillatory discharge around 30 Hz is explained i n a second model by the presence of intrinsically oscillatory cells wi thin cortical layer 5. Both models generate spike trains whose power s pectra 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 oscillator y discharge in the cat's visual cortex. The validity of these models i s consistent with the possibility that oscillations are generated inde pendently of intracortical interactions. Because these models rely on intrinsic stimulus-independent oscillators within the retina and corte x, the results further suggest that oscillatory activity within the co rtex is not necessarily associated with the processing of high-order v isual information.