Visual cortical input alters spatial tuning in monkey lateral geniculate nucleus cells.

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The response of monkey lateral geniculate nucleus (l.g.n.) cells to flashing spots, annuli, and drifting sine-wave gratings were recorded with tungsten micro-electrodes. These stimuli were presented (a) monocularly, through an aperture in the centre of a radial grating, or (b) dichoptically, in which the spots or drifting gratings were presented to the dominant eye's receptive field, while the centre of the radial grating was positioned on the corresponding retinal location of the other eye. Movement of the radial grating produced changes in the l.g.n. cell responses evoked by the spots and sine-wave gratings. These changes were reversed by cryogenic blockade of the striate cortex. Therefore, radial grating movement altered the responses of l.g.n. cells by activating the corticogeniculate (c.g.) pathway. In about half of all cells, radial grating-induced alterations of centre, or surround, or both responses to spots and annuli were produced. By adopting a simple spatial filtering model of the centre and surround mechanisms, it was possible to predict how these alterations in centre/surround balance would affect the cell's responses to sine-wave gratings. Alterations were observed in the peak and band width of the spatial and/or temporal tuning curves. The radial gratings did not alter the spatial summation properties of cells. Minor alterations in the spectral neutral points of chromatically opponent neurones were occasionally found. These results are interpreted as support for the view that spatial and temporal tuning are dynamic properties of some l.g.n. neurones by virtue of descending input from the visual cortex.

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