Visual pontocerebellar projections in the cat.

1. Projections of pontine visual cells onto the cat cerebellar cortex were studied by antidromic activation and by the retrograde transport of horseradish peroxidase (HRP). 2. Cells in the medial pontine visual area, which receive visual cortex projections, were activated antidromically principally from the contralateral cerebellar hemisphere. Cells in the dorsolateral pontine visual area, which receive an input from the superior colliculus, were activated principally from the vermis and ipsilateral hemisphere. There is some overlap in the projections of these two different populations of pontine cells, which probably occurs by way of bifurcated axons. 3. The HRP technique confirmed that there is a major difference in the pattern of projections from these two pontine visual regions. Many cells in the rostral-medial portion of the pontine nuclei, which receive their input from visual cortex, were labeled following HRP injections in the contralateral cerebellar hemisphere. Far fewer of these cells were labeled following vermal injection. Cells in the dorsolateral pontine nucleus, which receive visual input from the superior colliculus, were labeled following an HRP injection in the vermis or the ipsilateral hemisphere. Cells in the region of pontine nuclei that receive input from the ventral lateral geniculate nucleus were also labeled after a vermian injection. 4. If the vermis is related to the control of whole-body movements and the hemisphere to control of ipsilateral limbs, these results suggest that the corticopontocerebellar and the tectopontocerebellar pathways may be involved in different classes of visually guided movement.