Abstract
Pupil size changes constantly, mainly to regulate the amount of light entering to the retina, with pupil constriction to luminance increases and dilation to luminance decreases. This illumination-dependent pupil modulation has thought to be independent from the top-down influence such as spatial attention. However, it was shown recently that pupil size is smaller when spatial attention is guided to bright, compared to, dark surfaces, demonstrating the attentional modulation on illumination-dependent pupillary responses, although the underlying neural mechanism is yet explored. The superior colliculus (SC) is a midbrain structure causally involved in various components of orienting, including spatial attention. Here, we examined the attentional modulation of illumination-dependent pupillary responses by microstimulation of the SC (~70 Hz, 400 ms, 4 – 30 μA). We hypothesize that microstimulation of a specific location in the SC map will enhance sensory processing at the corresponding region of space (mimicking spatial attention shifts), inducing the illumination-dependent pupillary response (smaller pupil size in bright, compared to dark, surfaces presented in the region). While requiring monkeys to maintain central fixation, we presented bright and dark surfaces in two different locations that matched either the stimulated SC site or a control location in the opposite hemifield. We found that SC microstimulation modulated pupillary light responses in a spatially selective manner, with enhanced illumination-dependent pupillary responses while stimuli presented at the location corresponding to the stimulated SC site. Our results provide direct evidence arguing that the SC is mediating the attentional modulation of pupillary light responses.
Meeting abstract presented at VSS 2016