Coherence and Phase Locking Disruption in Electromyograms of Patients with Amyotrophic Lateral Sclerosis

In motor neuron disease, the aim of therapy is to prevent or slow neuronal degeneration and early diagnosis is thus essential. Hypothesising that beta-band (15−30 Hz) is a measure of pathways integrity as shown in literature, coherence and PLF could be used as an electrophysiological indicator of upper and lower neuron integrity in patients with ALS. Before further analysis, synthetic EMG signals were computed to verify the used algorithm. Coherence and PLF analyses were performed for instants of steady contraction from contra and ipsilateral acquisitions. Ipsilateral acquisitions were performed for one member of each group and results present significant differences between both groups. Contrarily, contralateral acquisitions were performed on 6 members of each group and results present no significant differences. PLF analysis was computed for ipsilateral acquisitions and, similarly to coherence, results show significant differences between both groups. PLF was also analysed for contralateral acquisitions, and results show no significant differences within groups, as expected since no coherence was found for the same acquisitions. So, while control subjects present no neuronal or muscular problems and therefore higher synchrony and coherence for beta-band frequencies, patients with ALS do not present synchronism or coherence in any frequency, specially for beta-band. All results allowed to conclude that contralateral coherence is not a good measure of corticospinal pathways integrity. However, ipsilateral acquisitions show promising results and it is possible to affirm that ipsilateral measurements may reflect neuronal degeneration. For future work is suggested a deeper analysis of PLF, that appear to have potential as a quantitative test of upper and lower neuron integrity related to ALS.