Basal ganglia high-frequency activity is co-modulated with the phase of motor cortical beta and shifted between the subthalamic nucleus and the internal pallidum during sustained motor control

Beta oscillations are readily observed in motor cortex and the basal ganglia, but to which extent they are functionally relevant is unclear. To understand how activity transfer between different nodes of the cortico-basal ganglia network is affected by cortical beta oscillations in different behavioural conditions, we recorded local field potentials and electroencephalography (EEG) activity in a low-force motor control task and during rest in Parkinson's patients undergoing deep brain stimulation (DBS) surgery. The patients received DBS of either the subthalamic nucleus (STN) or the internal globus pallidus (GPi), which allowed us to investigate if STN and GPi broad-band high-frequency activity (HFA; >150 Hz) is co-modulated with the phase of motor cortical beta activity. We found significant modulation patterns in the STN and the GPi, which were inverted while patients performed the task, showing that GPi activity fluctuations likely are crafted by other inputs than the direct excitatory STN afferents. We also found that consistent STN modulation disappeared during rest, showing disengagement in this condition, while GPi modulation was maintained, again evidencing that beta-band activity fluctuations in the GPi can be relatively independent of those in the STN. The difference between HFA modulation patterns in the task and rest recordings suggests a potential functional role of beta phase-locked HFA modulation in controlling sustained contractions. Examination of HFA co-modulation patterns at different sites of the cortico-basal ganglia-thalamo-cortical network under different behavioural conditions may provide a tool with which to define the impact of beta synchronization on network communication.