Slowing of reaction time in Parkinson's disease: the involvement of the frontal lobes

This study investigated the possibility that the previously mixed findings relating to cognitive deficits in Parkinson's disease might be attributable to inhomogeneity within the patients sampled, with attentional deficits oc curring only for those Parkinson's patients who also have additional fronta l lobe impairment. Twenty-five patients with idiopathic Parkinson's disease were classified as showing frontal dysfunction, or not, on the basis of th eir performance on the Wisconsin Card Sorting Test and the picture arrangem ent subtest of the WAIS. The two groups, and a control group of normal elde rly subjects matched for age and IQ, undertook tests of visual attention de signed to dissociate baseline response speed from central information proce ssing speed. Error rates did not differ between the groups. Performance of the non-frontally impaired Parkinson's group was indistinguishable from tha t of the controls. By contrast, the 'frontally impaired' Parkinson's group responded significantly more slowly than the controls. Further analyses ind icated that for the frontally-impaired Parkinson's group, information proce ssing and automatic functions were unimpaired but there was a generalised s lowing (as reflected by increased baseline response time) which may represe nt a non-specific global cognitive impairment. These findings suggest that the frontal lobes may be implicated in slowed response speed in Parkinson's disease. (C) 1999 Elsevier Science Ltd. All rights reserved.