Differential EEG Synchronization at Thalamic, Subthalamic and Cortical Levels during a Choice-Reaction Time Task

Basal ganglia nuclei are involved in diverse operations, motor and non-motor. Here, we identified EEG changes during a choice-reaction time task (CRT) at different brain levels, expressed as event-related synchronizations (ERS) and desynchronizations (ERD). Access to the thalamic ventral intermediate nucleus (VIM) and subthalamic nucleus (STN) was achieved during the externalization of electrode leads for deep brain stimulation (DBS). Recordings were performed in 7 patients with essential tremor and bilateral VIM implants (n=14), and in 3 patients with STN implants (n=6) for Parkinson's disease. EEG was recorded from two bipolar channels per depth-electrode and from 20 scalp positions. Randomized visual Go-signals, 1s after a pre-cue, were instructive for a button press with either the left or right index finger. The pre-cues followed the reaction to Go-signals by 2s. Off-line, band-pass filters were set from 8–13 and 14–35Hz. Referenced to the Go-signal, ERS and ERD were determined band-wise from -1s to +1.5s. Baseline-power was determined over 0.7s before pre-cues. Statistics were calculated with ANOVAs for repeated measurements. In the Alpha-band, a thalamic ERS of 20% was seen 100–250 ms after the pre-cue and Go-signal. Over sensorimotor scalp regions, a similar ERS pattern was seen, but this was followed by an ERD of 30% upon the pre-cue and 60% upon the Go-signal. In the subthalamus, ERS upon the pre-cue was comparable to that at scalp and thalamic levels, but upon the Go-signal it exceeded 100% and persisted through-out the analysis interval. At all levels similar Beta-changes were seen with a small ERD upon the pre-cue, and a pronounced ERD upon the Go-signal. Neither band change was lateralized. The differences between Alpha- and Beta-band and those between thalamic and scalp sites in the Alpha-Band were statistically significant. In the thalamus, pre-cue and Go-signals lead to identical changes in the Alpha-band, irrespective of their motor content, and compatible with mechanisms mobilizing event-related arousal. In contrast, at cortical and subthalamic sites, the Alpha-modulation correlated with the instructive value of the presented signal. The ERD in the 14–35Hz spectrum was similar across recording sites, compatible with the hypothesis of an antikinetic role of distributed neuronal populations, synchronising in the Beta-band. Thus, ERS-ERD-patterns correlate with motor and non-motor brain functions in a site- and band-specific way.