Cognitive disorders in Parkinson's disease without dementia]

The cognitive disorders observed in non-demented Parkinsonian patients are frequent but subtle. They mostly result from difficulties to control attentional resources. These deficits particularly disturb the strategies involved in planning as well as in encoding and retrieval processing of memory, whereas consolidation of the mnemonic traces and instrumental functions are relatively spared. These deficits can be related to the striatal dopamine depletion (in particular in the caudate nuclei) which seems sufficient to account for the cognitive disorders that appear early in the course of the disease. In particular, the caudate dopamine depletion induces a cascade of dysfunction within the basal ganglia, downstream of the striatum, which ultimately affects the prefrontal functions. It is likely that, in the course of the disease, lesions of other ascending systems of neurotransmission (cholinergic, serotoninergic and noradrenergic pathways) contribute to worsen the cognitive disorders and also to modify their clinical pattern. The impact of direct cortical lesions can also be discussed but it seems that these lesions mostly contribute to the cognitive deficits in the late stages of Parkinson's disease.