Investigation of brain dynamics in Parkinson's disease by methods derived from nonlinear dynamics

EEGs were recorded from patients in early stages of Parkinson's disease (17 patients, 9 females) and healthy controls (12 subjects, 8 females) during rest and during execution/imagining of a complex motor task. The prediction that Parkinson's disease patients compared to controls would show more com plex brain dynamics during performance of a complex motor task and imaginat ion of the movements was confirmed by methods derived from nonlinear dynami cs. In the resting state, analysis of con-elation dimension of EEG time ser ies revealed only slight topographical differences between the groups. Duri ng performance of a complex motor task, however, data from Parkinson's dise ase patients showed higher dimensionality than data from controls, indicati ng more complex EEG time series. The same difference was found when subject s did not perform any motor movements but imagined the complex movements th ey had just performed. The data are consistent with the hypothesis that the disturbances in Parkinson's disease result in the recruitment of superfluo us cortical networks due to failed inhibition of alternative motor programs in the striatum and thus increase the complexity of cortical representatio n in motor conditions.