Event:

Like in other species, the primate visual system is characterized by multiple parallel processing streams, besides the geniculostriate pathway. However, unlike in some of these species, the functional significance of alternative visual pathways remains unknown. To investigate the differential roles of geniculostriate versus alternative pathways, we performed focal, reversible inactivation of the primary visual cortex (V1) and studied a robust oculomotor phenomenon, called saccadic inhibition. This reflexive phenomenon, believed to rely on subcortical eye-movement control circuits (Buonocore and Hafed, 2023), is characterized by an obligatory short-latency cessation of saccade generation after visual stimulus onset, as well as by a concomitant saccade direction biasing, first towards and then away from stimulus location. Our prior work has shown that this phenomenon is immune to inactivation of both the superior colliculus (SC) and frontal eye fields (FEF). However, with V1 inactivation, saccadic inhibition was completely abolished, confirming a dominance of the geniculostriate pathway, even for this reflexive behavior. However, why do alternative visual pathways exist at all? We hypothesized that such pathways might still be functional, albeit in a gated manner. During V1 inactivation, we paired a visual onset in the blind field with a sound pulse that was completely uninformative about the visual stimulus location. Saccadic inhibition was now partially restored, and it was stronger and earlier than when the sound pulse occurred alone. Most importantly, there was a re-emergence of saccade direction biasing towards the visual stimulus location, even though the sound itself was not spatially informative. Moreover, we found evidence of residual, sound-gated, visual signals in both the SC and inferior colliculus (IC). These results demonstrate that multi-sensory information can activate an otherwise dormant visual-motor pathway bypassing V1, and they inform models of active visually-guided behavior invoking parallel sensory streams.


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