execution. Although abnormal dynPAC modulation was associated with slowed muscle recruitment during onset of slow tapping, the magnitude of PAC change did not correlate with the magnitude of the EMG slope. This suggests a complex and non-linear relationship between dynPAC and the build-up of corticospinal neuronal activity. Interestingly, studies probing cortical physiology in the preparatory phase of voluntary movements have provided similar evidence, suggesting that bradykinesia does not result from a single deficient physiological mechanism such as the ability to release ongoing inhibition (42, 43), but reflects a more complex circuit abnormality (44). Notably, in dynamic systems theory of motor control, preparatory activity is sensitive to timing events supporting motor transitions (18). However, it does not reflect specific movement features (e.g., direction, force, velocity), nor does it simply represent the release from inhibition of a motor program (45).
