Researching a differential impairment of frontal functions and explicit memory in early Parkinson's disease

An impairment at tasks sensitive to frontal lobe damage has been repeatedly reported in Parkinson's disease, but the exact nature of these deficits ha s not yet been clarified. Similarly, deficits of visuo-spatial functions ha ve been frequently observed, but it is still debated whether verbal and vis uo-spatial memory can be differentially affected. In this study we have com pared the performance of 20 mild Parkinson's disease patients (I-II Hoehn a nd Yahr stage) and 18 matched normal controls, at tasks assessing frontal f unctions and explicit memory. We detected a selective deficit in set shifting and maintaining, without im pairment in categorization and set formation. The lack of a selective incre ase in perseverative errors might indicate that perseverations either measu re something different from set shifting or that they do not represent an i ndex sensitive enough to set shifting impairment. Parkinson's disease patients were also significantly impaired at Raven's Pr ogressive Matrices, a task assessing both frontal and visuo-spatial aspects . However, they did not show any differential impairment of visuo-spatial m emory. Indeed, despite a trend of lower performance in visuo-spatial learni ng, memory performance of Parkinson's disease patients was significantly di fferent from that of controls only at a free recall test which involved bot h verbal and visuo-spatial memory. We suggest the exploration of set shifting and maintaining to detect 'front al' deficits in mild Parkinson's disease. We argue that Raven's Progressive Matrices is a valuable task for detecting subclinical cognitive deficits i n Parkinson's disease, even if it does not show a specific profile of impai rment in these patients. According to our results, a differential evaluatio n of verbal vs. visuo-spatial memory is not necessary in clinical practice, whilst free recall confirms its usefulness to detect subclinical impairmen ts of memory functions.