Response characteristics of neurons in the pulvinar of awake cats to saccades and to visual stimulation
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We studied responses of pulvinar neurons in awake cats that were allowed to execute spontaneous eye movements. Extracellular cell activity during saccades, saccade-like image shifts, and various stationary visual stimuli was recorded together with the animals' eye positions. All neurons analyzed had receptive fields that covered most of the central 80×80° of the animals' visual field and did only respond to large (>20°) visual stimuli. According to their response properties, recorded neurons were divided into three populations. The first group, termed "S neurons" (16%), responded when the animals performed saccades but were unresponsive to any of the visual stimuli tested. These neurons do not seem to receive a visual input that is strong enough to drive them. The second group, termed "V neurons" (51%), responded to various visual stimuli including saccade-like image motion when the eyes were stationary, but not when the animals executed saccades. V neurons therefore distinguish retinal image movements that are generated externally from internally generated image motion. Finally, "SV neurons" (31%) responded when the animals made saccades as well as to saccade-like image motion or to stationary stimuli. Although these neurons do not distinguish self-induced retinal image motion from motion generated by external stimulus movements, they must receive non-retinal motion-related input, because responses elicited by saccades had shorter latencies than responses to saccade-like stimulus movements. Only SV neurons resemble response properties of pretectal neurons that project to the pulvinar and that comprise the major subcortical visual input. The functional significance of pulvinar neuronal populations for visual and visuomotor information processing is discussed.
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