Bradykinesia (slowness of motor execution) and movement amplitude decrement during repetitive movements are cardinal kinematic abnormalities in patients with PD (22). Other movement parameters, such as grip force (23), patients’ natural tapping rate (24), or the ability to tap in sync with a pacemaker (25), do not reliably distinguish between patients and controls. The co-occurrence of pathological and intact motor behavior in patients with PD makes it possible to compare different movement types and elucidate the role of abnormal neuronal population dynamics underlying the movement impairment. If a physiological characteristic such as β-γ PAC is found to be abnormal during a kinematically normal motor behavior, it may be that the characteristic is insufficient for making the motor behavior abnormal. Conversely, if we find that a particular physiological abnormality is not present during a kinematically abnormal motor behavior then this abnormality may not be necessary for making the motor behavior abnormal.
