Differential distribution of barrel or visual cortex. Evoked responses along the rostro-caudal axis of the peri- and postrhinal cortices.

The functional connections between the barrel cortex and visual cortex on the one hand and the perirhinal (PER) and postrhinal (POR) cortices on the other hand were investigated in the rat. Stimulation of the barrel cortex evoked field potentials throughout the longitudinal extent of both PER and POR. In contrast, visual cortex stimulation evoked responses only in the caudal portion of PER as well as in POR. Therefore, the information from the visual cortex on the way to the hippocampus is transferred preferentially by a relay in POR, whereas somatosensory information is transferred via both PER and POR. Moreover, stimulation of both cortical regions elicited firing of multiple units; however, unit activity was more commonly found in POR than in PER. We conclude that the transfer of somatosensory and visual information to the hippocampal formation is preferentially mediated by parallel channels through PER and POR respectively. Although the information transfer through these channels does overlap to some extent, each channel appears to have specific properties.