Light-evoked cortical activity produced by illumination of intracranial retinal transplants: experimental studies in rats.

We have investigated whether information relayed through intracranial retinal transplants can elicit responses in the visual cortex of host rats. Embryonic retinae were transplanted over the midbrain of neonatal rats. Four to eight weeks later, the transplants were exposed and stimulated with light flashes. This photic stimulation elicited both evoked responses and multi-unit activity in area 18a of the visual cortex. Pathway tracing studies using horseradish peroxidase showed that these responses are transmitted to the cortex via the superior colliculus, the lateral division of the lateral posterior nucleus of the thalamus, and possibly the medial portion of the dorsal lateral geniculate nucleus. It is suggested that this pathway may be involved in complex transplant-mediated visual behaviors.