Demonstration of Early Cognitive Impairment in Parkinson's Disease with Visual P300 Responses.

INTRODUCTION: Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease. Cognitive changes in PD are less observable than motor symptoms; thus, research on cognitive processes, which are known to be impaired from the early stages of PD, is minimal. The purpose of this study is to research the brain dynamics of cognitively normal PD patients and healthy elderly controls using event-related potentials (ERPs) and to evaluate their relationships with neuropsychological tests. METHODS: Eighteen cognitively normal PD patients and 18 age-, gender-, and education-matched healthy controls were included in the study. Detailed neuropsychological tests were applied to all participants. Electroencephalography (EEG) was performed according to the international 10-20 system, and a classical visual oddball paradigm was used in the experiments. ERP responses in the 0.5 to 25 Hz frequency range were examined. P300 amplitude and latency values were measured from the F3, Fz, F4, C3, Cz, C4, P3, Pz, P4, O1, Oz, and O2 electrode sites. In addition, the correlations between P300 responses and neuropsychological test scores were analyzed. RESULTS: Significant differences were found between the P300 amplitudes of cognitively normal PD patients and healthy elderly controls [F(1,31)=9.265; p=0.005]. P300 amplitudes were significantly lower for PD patients at the F3, FZ, Cz, C4, Pz, and P4 electrode sites than for healthy elderly controls. Moderate correlations were found between Stroop test score and P4 amplitude, digit span forward and C3 and Pz amplitude, and digit span backward and O1 amplitude. CONCLUSION: The major finding of this study was the detection of cognitive changes by electrophysiological methods in PD patients who were indicated to be cognitively normal by neuropsychological tests. These finding suggests that cognitive changes in PD patients, which are not yet reflected in neuropsychological tests, may be detected by electrophysiological methods in earlier stages.