Electroencephalographic lateralization, clinical correlates and pharmacological response in untreated Parkinson's disease.

Background: In Parkinson's disease (PD), different topographically defined cortical-subcortical oscillatory networks have been implicated in motor program dysfunction. Few studies have focused on clinical correlates of cortical activity asymmetry using quantitative electroencephalography.

Methods: We retrospectively selected N = 34 L-dopa naïve PD subjects who had undergone standardized electroencephalography. We selected N = 18 subjects group-matched by age, sex and hand dominance with normal electroencephalography and no parkinsonism and/or cognitive decline as controls. A Welch's periodogram was applied to electroencephalographic signal epochs recorded from homologous pairs of electrodes over each hemisphere. An index of lateralization was then obtained as the absolute value of the electroencephalographic asymmetry index, computed by subtracting left from right-sided log power spectral density for each homologous site and frequency band. A standardized L-dopa acute challenge test was performed on all PD subjects to compute short-duration response magnitude.

Results: In mid/lateral frontal regions higher index of lateralization for the beta band (p = 0.015) and lower index of lateralization for the theta band (p = 0.036) were found in PD subjects as compared to controls. Both parameters correlated with Hoehn-Yahr staging (beta: r = 0.428, p = 0.012; theta: r = -0.464, p = 0.006). In occipital region lower index of lateralization for the alpha band was found in PD correlating with L-dopa short-duration response magnitude (r = 0.456; p = 0.007).

Conclusions: Lateralization of frontal cortex beta electroencephalographic activity is associated with clinical disability. Occipital cortex alpha activity may relate to L-dopa responsiveness in untreated PD subjects.