CORTTICAL AREA 5 IS NECESSARY FOR LONG-LASTING MEMORIES OF OBSTACLES ENCOUNTERED BY WALKKING CATS

Vision is used by walking animals to ensure stable foot placements and to avoid obstacles in their path. Visual input is not used directly when walking over normal terrain, however. Instead, walking animals look three or four steps ahead of their current position and use short-term memory to remember pertinent objects for use at the appropriate time. In cluttered terrain, humans may rely on increased visual input, guiding foot movement directly when needed. In quadrupeds, the hindlegs can never beguided by visual input directly, suggesting a specialized memory system mightbe used during walking in cluttered terrain. We have previously reported evidence in support of this hypothesis, showing that cats that have stepped over an object with their forelegs and stopped remember its position for much longer (for up to ten minutes) than if they are stopped prior to stepping over it. In this presentation, I present research that tests the hypothesis that neural signals related to the movement of the forelegs are essential for the generation of this unique visual memory. By placing small lesions in cortical area 5, we disrupted the normal integration of sensory and motor signals in the parietal cortex. Cats with these lesions lost the long-lasting memory of straddled objects, and remembered these objects for no longer than if they had not stepped over them. The results support our hypothesis that a uniquely long-lasting memory system, initiated by neural signals related to foreleg stepping, is responsible for guiding the hindlegs of walking cats over obstacles. Funding from Canadian Institutes of Health Research and Alberta Heritage Foundation for Medical Research gratefully acknowledged.