[Parkinson disease and cognition]

Parkinson's Disease patients may have cognitive deficits, which may vary from mild focal specific deficits to global dementia. Executive functions, working memory, visuoespatial functions and internal control of attention are the main affected cognitive areas. The dopaminergic hypothesis suggests that dopaminergic transmission is involved in most altered cognitive processes. However, other neuronal systems are probably implicated, and the improvement of the cognitive function after dopaminergic replacement is incomplete and not seen in all cognitive tasks. The prevalence of dementia in Parkinson's disease is estimated in 15-25%. The pathologic hallmarks may be similar to that seen in Alzheimer's disease. However, in Parkinson's disease patients pure subcortical alterations are able to produce a severe cognitive impairment, such as lost of dopaminergic neurones from substantia nigra to caudate nucleus and frontal areas. Comprehension of the relationship between depression and dementia in Parkinson's disease patients is incomplete. Parkinson's disease patients with depression show poor neuropsychological performance, especially in frontal tasks, but it is unclear whether depression can be considered a risk factor for the development of dementia in Parkinson's disease.