Development of diagnostic system for cognitive impairments in Parkinson's Disease

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Previous studies showed that cognitive functions could be impaired in patients with Parkinson's disease (PD). However, only cognitive impairments concerning executive functions and memory (procedural memory) were reported so far. In the present study, we examined whether or not PD patients have cognitive impairments other than those in the above, using behavior analysis and EEG (event-related potentials : ERP). The following results were obtained. (1) Our previous study showed that recognition of specific facial expressions (fear and disgust) is impaired in PD patients (Kan et al.2002). Supporting this finding, our recent study using ERP showed uniqueness of facial recognition in PD patients. The ERP study using dipole-tracing technique indicated that the amygdala and the pre-motor cortex were not active during the facial expression recognition task, whereas these areas were active in the normal control. The result suggests that the amygdala could be damaged in PD patients, as well as the basal ganglia (Yoshimura et al.2005). (2) Recently, the tasks concerning "theory of mind" and "social decision-making" are used to assess the frontal-lobe functions. Since it was hypothesized that the frontal lobe would be dysfunctioning in PD patients, we examined how PD patients would perform those tasks. The results showed that PD patients performed poorly in a "theory of mind" task in which they were asked to infer the thoughts/feelings of others, and that social decision-making was also impaired in PD patients (Oheda et al, in preparation).In conclusion, the present study demonstrated that PD patients have deficits in recognition of facial expressions and in social cognition, as well as deficits in executive functions and procedural memory. In addition, the present study provided us a diagnostic tool by which we can examine clinical symptoms caused by the brain damage in the areas other than the basal ganglia, in PD patients.