Spatial, but not object, delayed response is impaired in early Parkinson's disease.

The authors hypothesized that the pathophysiology of early Parkinson's disease (PD) may selectively target structures that support visual working memory for spatial relations but leave structures that support working memory for featural characteristics of objects relatively intact. Fifteen PD and 15 normal control participants took a visual delayed-response test with a spatial condition and a (nonspatial) object condition, equating the perceptual difficulty of the tests for each participant. The stimuli were irregular polygons presented at different locations on a computer screen. Results revealed a selective impairment of spatial delayed response in PD, indicating a disruption of spatial working memory unconfounded by sensory processing difficulties. The selectivity of this deficit may reflect the circumscribed nature of pathophysiological change affecting the caudate nucleus in early PD.