Premovement activities in the subthalamic area of patients with Parkinson's disease and their dependence on task

Movement preparation and execution are associated with a reduction in oscillatory synchrony over 6-35 Hz (event-related desynchronization; ERD) and increases in oscillatory synchrony at higher frequencies (event-related synchronization; ERS) in the human parkinsonian subthalamic nucleus (STN). The timing of the ERD < 35 Hz in STN correlates with, but precedes, the timing of voluntary movement, in line with a role in motor processing. Here, we explore how directly the synchrony manifest in local field potential (LFP) activities depends on the details of motor processing. To this end, we recorded local field potentials from the STN area of parkinsonian subjects while they performed internally paced single movements or double movements with one hand. Analysis was limited to time periods that were unequivocally premovement, so as to avoid the confounding effects of sensory afferance during movement. LFP power differed from baseline activity as early as 2.1-1.1 s prior to movement over 6-18 Hz and 56-70 Hz. However, only the early changes in LFP power in the 56-70 Hz band depended on task type. Later on, within 0.5 s of the forthcoming movement, the behaviour of both the 6-18 and 56-70 Hz bands differed according to movement type. In addition, a change was seen in LFP activity over 23-35 Hz, although the ERD in this band remained similar across movement types. The findings further implicate the human STN in the feedforward organization of movement in premotor circuits. Different aspects of this organization may be preferentially reflected in changes in synchrony at different frequencies.