(13–15). Increased resting β-γ PAC and β power have been found in subcortical nuclei of patients with PD (8, 11). However, at the cortical level, enhanced β-γ PAC at rest was more pronounced than enhanced β power (9, 13, 15). In addition, unlike the coupling between β phase and the relatively narrow γ band (around 250 Hz) found in subcortical nuclei of patients with PD (11, 12), the γ activity involved in the exaggerated cortical PAC were more broadband (50–200 Hz derived from ECoG and 50–150 Hz derived from scalp EEG) (8, 9, 14). Although this clearly suggests distinct underlying generative mechanisms, the wide range of γ oscillations in EEG and ECoG recordings could also result from the overlap of a large number of variably coupled local oscillators with different spectral and temporal properties (for an overview on the generative mechanism of γ, see Ref. 16). However, such a relationship between cortical PAC and motor impairment of PD may be difficult to interpret when determined in the absence of movement or impairment of movement.
