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Chin-An Wang, Susan Boehnke, Brian White, Douglas Munoz; Subthreshold microstimulation of the superior colliculus induces pupil dilation. Journal of Vision 2011;11(11):189. doi: 10.1167/11.11.189.
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The orienting reflex involves a wide repertoire of behavioral and physiological responses that includes not only a rapid shift of gaze, but also pupil dilation (Sokolov, 1963). The superior colliculus (SC) is a critical structure in the brain network that coordinates orienting behaviors, such as overt movements of eyes and head and covert shifts of attention. We sought to examine the role of the SC in pupil dynamics. First, we monitored pupil diameter in two non-human primate subjects during a variety of visual and oculomotor tasks (i.e., step, gap, and delayed- saccades). Pupil size was negatively correlated with saccadic latency (i.e., greater dilation resulted in shorter saccadic latency), suggesting that the amplitude of pupil dilation may be an effective indicator of attentional/cognitive processing during oculomotor tasks. We then examined whether the SC contributes causally to pupil dilation. We delivered a subthreshold train of microstimulation to the SC [train at 300 Hz for 100 ms at current between 10–50 μA], so that saccades were not evoked. We found significant pupil dilation within 150 ms of stimulation onset. This suggests that the primate SC plays a causal role in inducing pupil dilation as part of the orienting reflex. The possible neural pathways of induced pupil dilation by the SC stimulation will be discussed. Sokolov, E. N. (1963). Perception and the conditioned reflex. New York: Macmillan.
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