Response properties in the pulvinar complex after neonatal ablation of the primary visual cortex

Injuries to specific areas of the brain (such as cerebrovascular accidents or surgical procedures) and particularly to the primary visual cortex, yield profound visual defects. The level of spared visual functions or residual vision depends on the extent and location of the lesion as well as the age at which the trauma occurs. For instance, in primate as well as non-primate species, it is well established that lesions in adulthood have a more profound effect than those occurring in young animals. The recovery of visually guided behavior observed after massive destruction of the occipital cortex in young animals across many species has been generally associated with the reorganization of the pathways from the extrageniculate thalamus to the spared visual cortex, i.e. the extrastriate areas. In this chapter, we present some evidence that the lateral posterior-pulvinar (LP-pulvinar) complex may contribute to maintaining visual capacities in brain-damaged cats. Our data indicate that the overall visual responsiveness of the lateral part of the LP (LPl) cells is not altered by the early removal of the visual cortex. However, some specific properties differ from those of intact animals: on average, LPl neurons in brain-damaged animals are more broadly tuned for orientation than that in intact cats. Spatial frequency tuning functions are also affected since most units in lesioned animals are of the low-pass type. Moreover, most LPl cells of lesioned cats responded to drifting gratings with modulated discharges and a linear spatial summation within their receptive field, a characteristic that is infrequently observed in intact animals. The change in LPl response properties observed in the present study is likely to come from the reorganization of cortical and retinal fibers reaching this extrageniculate nucleus.