Projections between visual cortex and pulvinar in the rat

The extrageniculate visual pathway, which carries visual information from the retina through the superficial layers of the superior colliculus and the pulvinar, is poorly understood. The pulvinar is thought to modulate information flow between cortical areas, and has been implicated in cognitive tasks like directing visually guided actions. In order to better understand the underlying circuitry, we performed retrograde injections of modified rabies virus in the visual cortex and pulvinar of the Long‐Evans rat. We found a relatively small population of cells projecting to primary visual cortex (V1), compared to a much larger population projecting to higher visual cortex. Reciprocal corticothalamic projections showed a similar result, implying that pulvinar does not play as big a role in directly modulating rodent V1 activity as previously thought. Unlike the geniculocortical pathway which interconnects only between the lateral geniculate nucleus and primary visual cortex (V1), the pulvinar has long been known to interconnect with most if not all of visual cortex. Here we show that pulvinar interconnectivity is actually more dominant with higher visual cortex (V2) than with V1. Thus, the pulvinocortical pathway does not likely play as big a role in directly modulating V1 activity as previously thought.