Neural subpopulations in marmoset area MT/MTC detect and discount saccade-related retinal motion

In a study examining the neural mechanisms of saccade-related suppression in areas MT and MTC of marmoset monkeys, researchers discovered a complex interplay between visual signals and corollary discharge. Contrary to previous theories, it appears that both visual cues and feedback signals contribute to this suppression of retinal motion perception, ensuring a stable visual experience despite rapid eye movements.

The study involved marmosets freely viewing natural images, blank backgrounds, or images simulating saccades, as well as making saccades in complete darkness. The results revealed a broad range of saccadic modulation among the neuronal population. Some neurons exhibited short latency excitatory responses to saccades, while others suppressed their activity during eye movements. A subset of neurons even displayed a bi-phasic response, beginning with suppression before rebounding with an excitatory effect.

Neurons showing early responses were often tuned to the direction of saccades, whether on natural images, blank screens, or in darkness, suggesting a role for corollary feedback in these neurons. However, these neurons also responded similarly to retinal motion induced by simulated saccades, even when the eyes remained still, indicating that they can integrate visual cues for saccadic motion.

Moreover, a subset of neurons responded robustly to simulated saccadic motion but showed negligible response to real saccades, effectively discounting saccade-induced motion. These neurons were characterized by broader spike waveforms, consistent with their likely role as excitatory projection neurons. This finding supports the idea that varied neural subpopulations in areas MT and MTC contribute differently to saccadic suppression, with some neurons favoring inhibitory mechanisms while others exhibit excitatory features.