Visual object and visuospatial cognition in Huntington's disease: implications for information processing in corticostriatal circuits.

The primate visual system contains two major streams of visual information processing. The ventral stream is directed into the inferior temporal cortex and is concerned with visual object cognition, whereas the dorsal stream is directed into the posterior parietal cortex and is concerned with visuospatial cognition. Both of these processing streams send projections to the basal ganglia, and the ventral stream may also receive reciprocal connections from the basal ganglia. Although a role for the basal ganglia in visual object and visuospatial cognition has been suggested, little work has been carried out in this area in humans. The primary site of neuropathology in Huntington's disease is the basal ganglia, and hence Huntington's disease provides an important model for the role of the human basal ganglia in visual object and visuospatial cognition, and its breakdown in disease. We examined performance on a wide battery of tests of both visual object and visuospatial recognition memory, working memory, attention, associative learning and perception, enabling us to specify more fully the role of the basal ganglia in visual object and visuospatial cognition, and the disruption of these processes in Huntington's disease. Huntington's disease patients exhibited deficits on tests of pattern and spatial recognition memory; showed impaired simultaneous matching and delay-independent delayed matching-to-sample deficits; showed spared accuracy but impaired reaction times in visual search; were impaired in spatial but not visual object working memory; and showed impaired pattern-location associative learning. The results of our investigations suggest a particular role for the striatum in context-dependent action selection, in line with current computational theories of basal ganglia function.