The Japanese journal of neuropsychology

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ArticleTitle	The forefront of researches on cognitive function in Parkinson's disease: cognitive impacts on fronto-basal-ganglia system from a stereotaxic viewpoint
Language	J
AuthorList	Tetsuhiro Maruyama
Affiliation	Department of Internal Medicine, Iida-City Municipal Hospital
Publication	Japanese Journal of Neuropsychology: 18 (3), 171-181, 2002
Received
Accepted
Abstract	Parkinson's disease (PD) mainly presents motor disturbance, such as resting tremor, muscle rigidity, and bradykinesia, as a result of dysfunction of the dopaminergic nervous system involved by degeneration of the substantia nigra. In recent years, however, it has been recognized that this disease sometimes shows cognitive dysfunctions in addition to the movement disorder. Lots of studies were reported about cognitive dysfunctions of Parkinson's disease in about 20 years since 1980's, but core of the neuropsychological disorder has been gradually made clear. Parkinson's disease, differed from cerebrovascular disorders, presents varied cognitive disorders peculiar to each stage (Hoehn & Yahr's stage) of the disease, because it has a slowly progressive course. In particular, it is worthy of notice that specific cognitive dysfunctions for PD can be observed from the early stages that the lesions limit to basal ganglia. These domains of the disorders are so-called executive functions, such as attentional set-shifting, working memory and planning, which are sensitive to frontal lobe damage. In many studies, a deficit in set-shifting has been found in PD, using a number of different paradigms (among others the Wisconsin Card Sorting Test). Notably, in recent studies an impaired extradimensional shifting (in which shifts are to different perceptual dimensions) has been found in the earlier stages of PD. The critical finding that dopaminergic medication beneficially affected performance on attentional set-shifting tasks in patients with PD, together with anatomical finding that dopamine transmission was most severely depleted in the striatum, suggest fronto-striatal abnormalities underlying mechanisms of these cognitive deficits. In a recent trend of research on cognitive functions in Parkinson's disease, much attention has been paid to studies about changes of cognitive functions after stereotaxic brain surgery as a direct brain operation into the basal ganglia. The stereotaxic surgery of PD is mainly divided into two procedures, such as ablative procedures (thalamotomy, GPi pallidotomy, subthalamotomy) and deep brain stimulation (DBS) (DBS of the Vim, DBS of the GPi, DBS of the STN). A number of knowledge about impact on cognitive function has been accumulated in both operative procedures. According to the neuropsychological examination into the patients with PD by our Shinshu University-Kakeyu Hospital stereotaxic surgery group, unilateral pallidotomy hardly affected cognitive functions. However, it became clear to deteriorate the only fluency function (verbal fluency and design fluency). On the other hand, as for the DBS, some impacts on cognitive functions by the bilateral DBS (GPi and STN) were reported in Europe and America. It is expected that a neural mechanism underlying cognitive dysfunctions in Parkinson's disease would be more elucidated with the further development of such therapeutic approaches in future.
Keywords	Parkinson's disease, cognitive dysfunction, frontal lobe, basal ganglia, sterotactic surgery