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Robert Marino, Ron Levy, Doug Munoz; Target luminance modulates saccadic behavior and visual sensory responses in the superior colliculus. Journal of Vision 2007;7(9):244. https://doi.org/10.1167/7.9.244.
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Oculomotor saccade tasks have been used as a behavioral tool for studying the neural processes underlying saccade initiation. However, the dependence of saccade latency on target luminance and the corresponding modulation of visual responses within oculomotor brain regions is not well understood. In this study we examined how neuronal sensory discharge related to the onset of visual targets is modulated by stimulus intensity in neurons within the Superior Colliculus (SC) and how this modulation affects saccadic performance. We recorded single and multi-unit cell activity in the SC of rhesus monkeys trained to perform oculomotor tasks designed to measure and dissociate visual and saccadic responses. Cells were classified by their respective visual and/or motor activity dissociated in the Visual Delay task. Each neuron's visual response was sub-characterized by its target related discharge after the onset of a visual stimulus that stochastically ranged in intensities from below 0.01 cd/m2 to11 cd/m2. Preliminary results show significant modulations in target related discharges in visually responsive SC neurons. Increases in target luminance lead to significant increases in the peak magnitude of the visual burst of neurons. Significant decreases were also seen in the visual response onset latency (ROL) and duration of the visual response with increasing target intensity. Paradoxical low frequency visual responses to ipsilateral targets were recorded that occurred later than the contralateral visual response in the SC. The timing of the luminance dependant ROL matched the expected onset times for express saccades determined from behavioral analysis. The consequences for express saccades imply that the later arrival and diminished response at dim targets can significantly affect express saccade latency and likelihood. From these data we conclude that target luminance can be used as a valuable tool for altering the timing and magnitude of sensory signals within the visual system leading to saccade initiation.
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