Phase–amplitude coupling has more commonly been ascribed a functional role for information processing within the brain (Jensen and Colgin, 2007). Our findings indicate that PAC may also serve as a pathological mechanism. One intriguing explanation for why exaggerated levels of beta–HFO PAC in the STN might lead to motor impairments is that the pro-kinetic HFO become locked by the beta band oscillation, which prevents them from initiating firing patterns underlying movement (López-Azcárate et al., 2010). Our partial correlations support this theory, demonstrating that UPDRS scores were more likely to be directly linked to PAC values than to beta power. Related to this, alpha–gamma coupling in the motor cortex has been found to decrease in anticipation of an upcoming cued movement (Yanagisawa et al., 2012). Hence the reduction of coupling with lower frequencies could free up resources for movement-related activity.
