The effect of somaesthetic and photic stimuli on the activity of units in the striate cortex of unanaesthetized, unrestrained cats.

A number of cells in the striate cortex of both cats and rabbits appear to respond to non-visual stimuli. These include vestibular, acoustic and nociceptive stimuli (Griisser, Griusser-Cornehls & Saur, 1959; Lomo & Mollica, 1962; Jung, Kornhuber & IDa Fonseca, 1963; Murata & Kameda, 1963) and electric shocks delivered to the sciatic nerve (Akimoto, Saito & Nakamura, 1961). Some of these units also respond to diffuse retinal illumination. The object of the present study was to analyse the way in which the response to binocular stimulation of cells in the visual cortex was modified by a somaesthetic stimulus. The experiments were done on conscious, mobile cats. This preparation has the advantage that anaesthetic drugs are not used when records are made, but the disadvantage that it is not easy to stimulate a known restricted area of the retina because of head and eye movements. It is, however, possible to illuminate the retina diffusely in such a way that the intensity and extent of retinal illumination are not affected by head and eye movements. Only relatively few cells in the cat striate cortex respond to such stimuli (Hubel, 1959), the response elicited by any one flash is variable (Burns, Heron & Grafstein, 1960) and the response is not as brisk as the response elicited by a discrete retinal stimulus (Hubel & Wiesel, 1959). Because of the last two factors, and because cells in the cortex of unanaesthetized cats show spontaneous impulse activity, quantitative parameters of the discharge were calculated to assess the magnitude of an apparent response to diffuse photic stimuli. A brief account of some of this work has been published elsewhere (Horn, 1963).

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