Slowing of reaction time in Parkinsons disease: theinvolvement of the frontal lobes

Abstract

This study investigated the possibility that the previously mixed findings relating tocognitive deficits in Parkinsons disease might be attributable to inhomogeneity within thepatients sampled, with attentional deficits occurring only for those Parkinsons patients who alsohave additional frontal lobe impairment. Twenty-five patients with idiopathic Parkinsons diseasewere classified as showing frontal dysfunction, or not, on the basis of their performance on theWisconsin Card Sorting Test and the picture arrangement subtest of the WAIS. The two groups,and a control group of normal elderly subjects matched for age and IQ, undertook tests of visualattention designed to dissociate baseline response speed from central information processingspeed. Error rates did not differ between the groups. Performance of the non-frontally impairedParkinsons group was indistinguishable from that of the controls. By contrast, the frontallyimpaired Parkinsons group responded significantly more slowly than the controls. Furtheranalyses indicated that for the frontally-impaired Parkinsons group, information processing andautomatic functions were unimpaired but there was a generalised slowing (as reflected byincreased baseline response time) which may represent a non-specific global cognitiveimpairment. These findings suggest that the frontal lobes may be implicated in slowed responsespeed in Parkinsons disease.