Recently, de Hemptinne et al. (2013) revealed a pathological coupling between the instantaneous phase of beta band oscillations and the amplitude of broad band gamma activity (50–200 Hz) in the primary motor cortex. This phase–amplitude coupling (PAC) was characteristic for Parkinson’s disease as it was absent for dystonia and epilepsy patients, and abolished during DBS (de Hemptinne et al., 2015). They observed a similar coupling between beta band oscillations recorded from the STN and broadband gamma activity in the primary motor cortex. The potential importance of PAC was further underscored by Shimamoto et al. (2013) who demonstrated that the magnitude of locking between spike activity in the STN and beta band oscillations in the primary motor cortex correlated with bradykinesia scores.
