Investigation of non-linear properties of multichannel EEG in the early stages of Parkinsonʹs disease

Objectives: Modifications of brain activity in the early stages of Parkinsonʹs disease (PD) are difficult to detect using electroencephalography (EEG) signals and are often biased by -DOPA treatment. We compare here the performances of both linear and non-linear methods in differentiating EEG of -DOPA naive PD patients from that of control subjects. Methods: Resting multichannel EEG (20 electrodes, 30 s epochs) of 9 patients with PD in Hoehn and Yahr stages 1–2 (4 women, 5 men, mean age 54.3 years, range 48–63 years) were compared with those of 9 control subjects (7 women, two men, mean age 51.3 years, range 43–61 years). The following measurements were computed: θ-, α- and β-band relative powers constituted the linear indices; localized entropy, slope asymmetry and number of non-linear EEG segments constituted the non-linear indices. Results: In the case of linear quantification, only a decrease in the β-band was observed for patients. Significant non-linear structures were observed in our EEG data. Non-linear quantifiers demonstrate an increase in entropy and in the number of non-linear EEG segments for the patients. Conclusions: Changes in EEG dynamics observed here in -DOPA naive PD patients may represent early signs of cortical dysfunction produced by subcortical dopamine depletion.