CEREBRAL CORTICAL MECHANISMS FOR EYE MOVEMENTS AND VISUAL ATTENTION

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Two lines of inquiry were followed to determine how the cerebral cortex and its efferent regions control eye movements and visuospatial attention. In one, we studied the activity of neurons in the posterior cingulate during various visuomotor tasks to determine their activity with respect to visual stimuli that were either spontaneously salient or used as the targets for saccades. Neurons that responded to salient visual stimuli, such as checkerboards, did not respond to small spots of light, even when those spots were used as targets for saccadic eye movements or as stimuli in a luminance-detection task. These results suggest that the brain treats voluntary attention differently from involuntary attention to salient and novel stimuli. The cingulate cortex is important in the generation of voluntary but not involuntary attention. The second line of inquiry was the study of visually responsive neurons in the superior colliculus. We used the visual stimulation engendered by eye movements to understand the effect of motor planning on the visual responsiveness of these neurons. For a distinct subpopulation of visuomovement neurons in the intermediate layers of the superior colliculus, the neurons would respond to visual stimuli that were about to be brought into their visual receptive fields by a saccadic eye movement. This predictive visual response resembled that previously described by this group for the lateral intraparietal area of the parietal cortex. It may well describe a general mechanism by which the brain achieves spatially accurate behavior.