THE LENGTH RESPONSE PROPERTIES OF CELLS IN THE FELINE PERIGENICULATE NUCLEUS

Perigeniculate cells receive visual input from the dorsal lateral geni culate nucleus (dLGN) and from the visual cortex. In contrast to the e xtensive literature documenting dLGN and cortical cell responses, comp aratively little quantitative data exists for perigeniculate nucleus c ells, and very little is known about the role of the corticofugal inpu t to the perigeniculate nucleus. We have previously shown that dLGN re lay cells have sharply length-tuned receptive fields and that a signif icant component of this is dependent on the corticofugal system. In th is report, we have explored the length-response properties of perigeni culate nucleus cells in the presence and absence of corticofugal feedb ack. The response profiles of most perigeniculate nucleus cells contra sted markedly with the sharply length-tuned fields of dLGN cells, but exhibited a notable resemblance to those exhibited by VI cells with sh ort summation lengths, which have recently been shown to constitute a considerable proportion of the layer VI cell population. This might su ggest that the responses of perigeniculate nucleus cells to long bars derive from their cortical input. However, our data failed to reveal a discernible change in their profiles after removal of the corticofuga l drive. This surprising observation implies that their length-tuning profiles follow from subcortical circuitry. The ways in which this mig ht occur are discussed.