Saccades cause rapid retinal-image shifts that go perceptually unnoticed several times per second. The mechanisms for saccadic suppression have been controversial, in part due to sparse understanding of neural substrates. Here we uncovered an unexpectedly specific neural locus for spatial-frequency specific saccadic suppression in the superior colliculus (SC). We first developed a sensitive behavioral measure of suppression in two macaque monkeys, demonstrating selectivity to low spatial frequencies similar to that observed in earlier behavioral studies. 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 behavior. Most importantly, suppression selectivity for spatial frequency in visual-motor neurons 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. Visual SC neurons had mild suppression, which was unselective for spatial frequency and thus only explaining up to ~48% of behavioral variance. In terms of spatial-frequency specific saccadic suppression, our results run contrary to predictions that may be associated with a hypothesized SC saccadic suppression mechanism, in which a motor command in the visual-motor and motor neurons is first relayed to the more superficial purely visual neurons to suppress them, and to then potentially be fed back to cortex. Instead, an extra-retinal modulatory signal mediating spatial-frequency specific suppression may already be established in visual-motor neurons.
- Superior colliculus
- Saccadic suppression
- Perceptual stability
- Copyright © 2016, Journal of Neurophysiology