Movement-related beta oscillations show high intra-individual reliability

Abstract

Oscillatory activity in the beta frequency range (15-30Hz) recorded from human sensorimotor cortex is of increasing interest as a putative biomarker of motor system function and dysfunction. Despite its increasing use in basic and clinical research, surprisingly little is known about the test-retest reliability of spectral power and peak frequency measures of beta oscillatory signals from sensorimotor cortex. Establishing that these beta measures are stable over time in healthy populations is a necessary precursor to their use in the clinic. Here, we used scalp electroencephalography (EEG) to evaluate intra-individual reliability of beta-band oscillations over six sessions, focusing on changes in beta activity during movement (Movement-Related Beta Desynchronization, MRBD) and after movement termination (Post-Movement Beta Rebound, PMBR). Subjects performed visually-cued unimanual wrist flexion and extension. We assessed Intraclass Correlation Coefficients (ICC) and between-session correlations for spectral power and peak frequency measures of movement-related and resting beta activity. Movement-related and resting beta power from both sensorimotor cortices was highly reliable across sessions. Resting beta power yielded highest reliability (average ICC=0.903), followed by MRBD (average ICC=0.886) and PMBR (average ICC=0.663). Notably, peak frequency measures yielded lower ICC values compared to the assessment of spectral power, particularly for movement-related beta activity (ICC=0.386-0.402). Our data highlight that power measures of movement-related beta oscillations are highly reliable, while corresponding peak frequency measures show greater intra-individual variability across sessions. Importantly, our finding that beta power estimates show high intra-individual reliability over time serves to validate the notion that these measures reflect meaningful individual differences that can be utilised in basic research and clinical studies.

Keywords: Beta oscillations; EEG; Intraclass correlation coefficient; Sensorimotor cortex; Test-retest reliability.

Fig. 1

Experimental setup and measurements. A, Experimental paradigm. Subjects sat in front of a computer monitor and were instructed to perform wrist movements to move the wrist cursor (red circle) from the initial start position (grey square) to one of two target positions (blue squares) upon target presentation. B, Calculation of reaction time (RT), movement time (MT) and peak velocity (PV) where the grey patch represents target presentation. Velocity profile (blue line) and wrist angular displacement (red line) are shown for one trial of an example participant. C, Topographical distribution (top panel) and time-frequency map (bottom panel) of movement-related beta activity. Topographical plots of grand-average beta power revealed electrodes of peak change (highlighted as black-and-white disks) overlying contra- and ipsilateral sensorimotor cortices. Time-frequency map for pooled electrodes contralateral to moving hand showing two distinct time windows of peak changes in beta activity (MRBD: 1–2 s; PMBR: 6–7 s). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article).

Fig. 2

Beta peak frequency detection using least square fit procedure to remove 1/f component from spectrum. A, Power spectrum of one example subject (subject 1) who did not show a clear peak in the beta frequency range (grey dashed rectangle). Black dashed line indicates 1/f component obtained from least square fit of log-log transformed data. Inset shows enlarged view of the spectrum for the beta frequency range. B, Corrected spectrum (after subtraction of 1/f component). Note that in the uncorrected spectrum (A) local maxima were found at 15 Hz or 18.2 Hz, whereas the peak is at 20.7 Hz in B.

Fig. 3

Average movement-related changes in spectral power for each EEG session. Topographies of relative power change in beta frequency (15–30 Hz) during and after movement are averaged over the time window of interest 1–2 s and 6–7 s for MRBD and PMBR, respectively, as indicated by the black rectangles. Time-frequency spectrograms are averaged across subjects separately for contralateral (upper panel) and ipsilateral (lower panel) sensorimotor cortex for all EEG sessions. The right hand panel displays overlaid beta power traces for the six sessions (S1=light blue, S2=orange, S3=yellow, S4=purple, S5=green, S6=blue). The black rectangles indicate the time window of interest (MRBD and PMBR) that were tested for significant differences between sessions and hemispheres. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article).

Fig. 4

Test-retest reliability of spectral power (A) and peak frequency (B) measures across separate sessions (S1–S6). Individual values were extracted for each EEG session from pre-selected electrodes overlying contralateral (grey shading) and ipsilateral sensorimotor cortex and distinct time windows (BB: 1–0 s; MRBD: 1–2 s; PMBR: 6–7 s). The degree of clustering gives a visual impression of the within-subject and between-subject variation. Black horizontal bars represent grand-mean (across sessions) for each subject.

Fig. 5

Test-retest reliability of spectral power (A) and peak frequency (B) measures of beta oscillatory activity derived from contralateral and ipsilateral sensorimotor cortices, respectively. Values given are intraclass correlations (ICCs). Grey vertical bars represent lower and upper boundaries of the ICC. ICCs>0.8 indicate almost perfect levels of agreement across sessions.

Fig. 6

Between-session (S1–S6) correlation coefficients and corresponding intraclass correlation coefficients (ICCs) for spectral power and peak frequency estimates for contralateral (grey shading) and ipsilateral sensorimotor cortices. The colour bar indicates the correlation coefficients (r) presented in the matrices. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article).