Electrophysiological and anatomical demonstration of an overlapping striate and tectal projection to the lateral posterior-pulvinar complex of the cat.

Extracellular unit activity was recorded in the lateral posterior (LP)-pulvinar complex. The responses of 254 neurons after electrical stimulation of the central-paracentral part of cortical area 17 and of 84 neurons after stimulation of both area 17 and the superior colliculus (SC) were investigated. Neurons in the LP-pulvinar complex responded to area 17-stimulation with excitatory-inhibitory effects; in some cases only with inhibition. Neurons affected by striate stimulation were found in the caudal region of the complex in a region that extended widely into the medial part of the lateralis posterior nucleus (LPm), the so-called tectorecipient part of the lateral posterior nucleus. Accordingly, 26 of the 84 neurons in which electrical stimulation of area 17 and of the SC was tested, were found to react to both types of stimulation. Cells responding only to SC-stimulation were found in the ventral region of the anterior LP-Pulvinar complex. Anatomical studies supported the finding that striate and tectal inputs overlap considerably in the LP-pulvinar complex. After depositing horseradish peroxidase (HRP) into various regions of the LP-pulvinar complex, retrogradely labeled cells were found in area 17 (layer V) as well as in the superficial layers of the SC. These results were confirmed by orthograde transport autoradiography after injection of labeled amino-acids into area 17. Our findings indicate that cortical and collicular inputs into the caudal part of the LP-pulvinar complex overlap considerably and that, in these overlapping regions, individual neurons may receive converging afferent excitation from both regions.