[Cognitive dysfunction in Parkinson's disease]

The neuropsychological impairments associated with Parkinson's disease(PD) have been often documented. However, the pathological mechanisms underlying cognitive dysfunction are hardly solved, as compared with motor dysfunction. Moreover, the precise relationships between the two dysfunctions have remained aloof. This paper attempts to clarify three specific domains of isolated cognitive impairments: dysexecutive syndrome, memory disturbance, and bradyphrenia, which are specifically observed in PD. It especially discusses the neuropsychological relationships between these impairments and the stages of illness. Several neuropsychological experiments to examine these three domains of cognitive impairments were conducted. Significant results were obtained in the following: set-shifting and divergent thinking were significantly impaired in both the early group and the advanced group; while set-maintaining, procedural learning, and cognitive speed, were only significantly disturbed in the advanced group. The failure to acquire procedural skills and the slowing of cognitive speed, were correlated with decreased attention of working memory in the advanced group. These results indicate that the shifting of cognitive sets maybe disturbed in the embryonic stage of the disease. The results also indicated that other cognitive dysfunctions might manifest themselves during the advanced stages due to attentional deficits. In conclusion, it is possible that other neurotransmitters maybe involved in the progressive degeneration of other systems in addition to the dopaminergic system. For example: serotoninergic, noradrenergic and cholinergic systems. Therefore, further research is required to establish which neurotransmitters are involved in their corresponding cognitive impairments in PD.