Fig. 1.
EEG β bursts are phase locked to spiking activity in the STN of PD patients. (A) BUA signals were recorded from 5 microelectrodes in the STN area together with EEG from the Fz–Cz position. As the microelectrodes traversed the STN, some electrodes were inside and some outside the structure. The layout of the 5 electrodes is shown within the red dotted circle. (B) Average BUA power spectrum from inside (red; n = 256 BUAs) and outside (gray; n = 222 BUAs) the STN, highlighting that enhanced rhythmic activity in the beta band (15 to 35 Hz) is observed inside the STN. (C) The proportion of BUA signals that are coherent with the EEG is selectively increased in the beta frequency range when electrodes were inside but not outside of the STN (number of recordings as in B). (D) An exemplary EEG β burst (black) from subject 1 (right hemisphere), together with simultaneously recorded STN-BUA (red). Onset of a cortical β burst was defined as the time point that the instantaneous beta amplitude exceeded the 75th percentile of the amplitude of the whole recording and remained elevated for at least 50 ms. Dashed line indicates the amplitude threshold for determining the onset of the EEG β burst. The beta amplitude of both the EEG and STN BUA simultaneously crosses the burst threshold and remains above it for around 200 ms (gray box). This increase in amplitude is visible in the raw (black) and filtered (gray) EEG signal. Bursts of activity in the STN BUA (raw, red; beta filtered, pink) are clearly aligned to the trough of the EEG beta oscillation during the burst. (E and F) Phase locking in time (E) and across bursts (F) around the onset of EEG β bursts (time 0; dotted line) between EEGβ and subthalamic BUAβ for different cortical β-burst durations (hemispheres = 13, patients = 7, n = 18 recordings; see color key for burst duration; see SI Appendix, Fig. S1, for schematic explanation of analysis methods). Significance for each burst length was determined using a cluster-based analysis (Methods) which tested the difference in the modulation of PSI over time in the burst-aligned data to that from randomly selected data that had no relationship to burst onset. Significant increases with respect to baseline are indicated with horizontal bars, color matched to the burst duration. B and C show mean and SEM across hemispheres. In E and F, shaded regions indicate the SEM across all recordings.