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Ziad M. Hafed; A neural locus for perceptually-relevant microsaccadic suppression in the primate superior colliculus. Journal of Vision 2017;17(7):7. doi: 10.1167/17.7.7.
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Microsaccades cause rapid retinal-image shifts that go perceptually unnoticed. The mechanisms for perceptual microsaccadic suppression are not well known; moreover, those for large saccades have been highly controversial, in part due to sparse understanding of neural substrates. Here we uncovered an unexpectedly specific neural locus for microsaccadic suppression in the superior colliculus (SC). We first developed a sensitive behavioral measure of perceptual suppression in two monkeys, demonstrating selectivity of microsaccadic suppression to low spatial frequencies. We then investigated visual responses in either purely visual SC neurons or anatomically-deeper visual-motor neurons, which are also involved in saccade generation commands. Surprisingly, visual-motor neurons showed the strongest visual suppression, and the suppression was dependent on spatial frequency like in perception. Most importantly, visual-motor neuron suppression selectivity was highly predictive of behavioral suppression effects in each individual animal, with our recorded population explaining up to ~74% of behavioral variance even on completely different experimental sessions. In contrast, purely visual neurons only had mild and unselective suppression. Because microsaccades are mechanistically similar to large saccades, our results illuminate the broader topic of saccadic suppression in general. Specifically, our results run directly contrary to a hypothesized SC mechanism for saccadic suppression, in which a motor command in the visual-motor and motor neurons is relayed to the more superficial purely visual neurons to suppress them, and to then potentially be fed back to cortex. Instead, our results indicate that an extra-retinal modulatory signal mediating perceptual suppression is already established in visual-motor neurons.
Meeting abstract presented at the 2016 OSA Fall Vision Meeting
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