THE LATERAL POSTERIOR-PULVINAR COMPLEX OF MAMMALS AND THE VISUAL FUNCTION

It is now well established that the lateral posterior-pulvinar (LP-P) complex of mammals is involved in visual processing. However, the actual function of these large nuclei of the thalamus remains unknown. In contrast to the nearby lateral geniculate nucleus, the LP-P complex does not receive any substantial direct projections from the retina. Its main visual inputs come from the mesencephalon and the neocortex. Most cells in the LP-P complex behave like cortical units. They are tuned to the orientation, direction, spatial and temporal frequencies of the visual stimulus. In addition, most units are binocular and sensitive to relative retinal disparity. Despite their multiple inputs, the LP-P complex cells form an homogeneous population and their overall properties do not reflect those of a given cortical or subcortical area. On the basis of its afferent and efferent connectivity, it has been proposed that the LP-P complex may serve as a relay of an extrageniculate ascendant pathway which originates from the superior colliculus, and/or provide another route for the geniculo-striate input to reach the extrastriate areas. Despite the fact that there is some electro-physiological evidence of such functions, it is now often suggested that the LP-P complex may integrate its multiple inputs and be involved in functions which go beyond those of a simple thalamic relay. Recent findings suggest that the LP-P complex might play a role in visual spatial attention.