3. Perisaccadic EEG components in Parkinson disease patients

Background Perisaccadic gamma power modulation is impaired for voluntary saccades (Forgacs et al., 2008) in Parkinson disease (PD) patients. Purpose To quantify both perisaccadic gamma (PG) and beta PB components of the EEG in PD. Method We quantified the anterior–posterior distribution of PG (35–45 Hz) and PB (18–24 Hz) range EEG in PD patients while they executed voluntary saccades, towards and away from their body–centers/central fixation. The EEG was recorded with Electro-cap over frontal, parietal, occipital and temporal scalp sites in 14 healthy subjects (age 55–72 yrs, 6 females) and in 11 PD patients (age 57–78 yrs, 5 females, H-Y stage 1–3). EOG and infrared reflections (ISCAN) simultaneously recorded eye movements. Subjects executed saccades to a mark 15° at right or left on a screen and back to fixation point/midline. 2 min EEG was obtained from each subject for each of the four possible saccades; rightwards R and leftwards L, towards (centripetal CP) and away from the midline (centrifugal CF) saccades. Each 500 ms window bracketing a saccade was analyzed using continuous wavelet transform (cWT). Single trial results were averaged after WT to obtain average gamma and also beta power values/coefficients for the perisaccadic time window. T -test was used to test for differences b/w PD and healthy subjects for frontal and parieto–occipital sites for both gamma and beta frequency ranges. Results (1) Average frontal PG power for healthy subjects; (CPR = 0.275, CFR = 0.27, CPL = 0.295, CFL = .285) vs. PD patients (CPR = 0.24, CFR = 0.22, CPL = 0.235, CFL = 0.235)_p = 0.0005. (2) Average parieto–occipital PG power for healthy subjects; (CPR = 0.235, CFR = 0.23, CPL = 0.23, CFL = 0.23) vs. PD patients (CPR = 0.28, CFR = 0.27, CPL = 0.28, CFL = 0.29)_p = 0.0006. (3) Average frontal PB power for healthy subjects; (CPR = 0.3, CFR = 0.29, CPL = 0.32, CFL = 0.31) vs. PD patients (CPR = 0.285, CFR = 0.275, CPL = 0.28, CFL = 0.29)_p = 0.03. (4) Average parieto–occipital PB power for healthy subjects; (CPR = 0.26, CFR = 0.27, CPL = 0.27, CFL = 0.27)) vs. PD patients (CPR = 0.31, CFR = 0.31, CPL = 0.31, CFL = 0.32)_p (5) ‘Frontal’ PG and PB powers (coefficients) attenuate while both the ‘parieto–occipital’ PG and PB power increase in PD patients vs. age matched healthy subjects for all kinds of voluntary saccades. This happens for all kinds of saccades. Healthy subjects = CPR ( R 2 = 0.9), CFR ( R 2 = 0.8), CPL ( R 2 = 0.9), CFL ( R 2 = 0.9) and PD patients = CPR ( R 2 = 0.3), CFR ( R 2 = 0.2), CPL ( R 2 = 0.2), CFL ( R 2 = 0.3). Discussion Several brain areas are involved in cortical control of voluntary saccades. BOLD MRI shows (Rieger et al. 2008) that the frontal eye field (FEF) is hypoactive in PD patients during execution of voluntary saccades. Our results i.e. lower ‘frontal’ PG and PB power in PD vs. healthy subjects suggest an association between the EEG (Bodis-Wollner, 2002; Forgacs et al., 2008; Javaid et al., 2010) and BOLD-MRI (hypoactive FEF) results in PD. Conclusion Cortical saccade control is impaired in PD. The perisaccadic EEG reveals ‘significantly’ lower frontal and higher parieto–occipital PG and PB powers in Parkinson patients vs. healthy subjects. PG and PB power co-vary when voluntary saccades are executed except at frontal recording sites in PD. Since BOLD reveals reduced perisaccadic frontal activity, our current EEG results suggest a potential link between BOLD and EEG data.