Opposing cortical forces: Alpha slowing and sensorimotor mu acceleration during motor-related BCI training
Fig 2
Representative example of EKF-tracked mu (a) frequency and (b) magnitude from channel C3 of a participant in the Schalk2004 dataset.
The top panels display the raw estimated trajectories (black) along with the best-fit linear trend (cyan). The estimated slope of the mu frequency was 1.128 Hz/hour (p < 0.05, after correction for multiple comparisons), while the mu magnitude increased at a rate of 2.458 a.u./hour (p < 0.05, after correction for multiple comparisons). The bottom panels show the slope change likelihood curves, quantifying the probability of abrupt trend shifts over time based on binary change point detection smoothed with a noncausal Gaussian kernel. In the mu frequency panel (bottom left), the slope change likelihood sharply peaks near the session start (~0–2 minutes), indicating a prominent early change in slope. This is consistent with the visible shift in the frequency trajectory shown in the top-left panel. In contrast, the mu magnitude panel (bottom right) exhibits a delayed and more gradual peak in slope change likelihood around 14–16 minutes. Visually inspecting (b) suggests that mu magnitude started stabilizing toward the session’s end.