  Extraction of the movement-related high-gamma (80 - 160 Hz) in
electroencephalogram (EEG) from traumatic brain injury (TBI) patients who have
had hemicraniectomies, remains challenging due to a confounding bandwidth
overlap with surface electromyogram (EMG) artifacts related to facial and head
movements. In part 1, we described an augmented independent component analysis
(ICA) approach for removal of EMG artifacts from EEG, and referred to as EMG
Reduction by Adding Sources of EMG (ERASE). Here, we tested ERASE on EEG
recorded from six TBI patients with hemicraniectomies while they performed a
thumb flexion task. ERASE removed a mean of 52 +/- 12% (mean +/- S.E.M)
(maximum 73%) of EMG artifacts. In contrast, conventional ICA removed a mean of
27 +/- 19\% (mean +/- S.E.M) of EMG artifacts from EEG. In particular,
high-gamma synchronization was significantly improved in the contralateral hand
motor cortex area within the hemicraniectomy site after ERASE was applied. We
computed fractal dimension (FD) of EEG high-gamma on each channel. We found
relative FD of high-gamma over hemicraniectomy after applying ERASE were
strongly correlated to the amplitude of finger flexion force. Results showed
that significant correlation coefficients across the electrodes related to
thumb flexion averaged 0.76, while the coefficients across the homologous
electrodes in non-hemicraniectomy areas were nearly 0. Across all subjects, an
average of 83% of electrodes significantly correlated with force was located in
the hemicraniectomy areas after applying ERASE. After conventional ICA, only
19% of electrodes with significant correlations were located in the
hemicraniectomy. These results indicated that the new approach isolated
electrophysiological features during finger motor activation while selectively
removing confounding EMG artifacts.
