dynamic systems theory of motor control (21). According to this theory, preparatory activity brings the dynamic state of the neuronal population through state-space rotations to an initial value. This process, which is characterized by brief cortical oscillatory activity (20), ensures that muscle activity can be generated efficiently for all types of movements (20, 21). If dynPAC reflects normal preparatory activity, then it is perhaps not surprising that movement-related PAC was found to be similar in patients with PD and patients with essential tremor (17), especially in the absence of kinematic differences between the patient groups.
