Simples Coherence vs. Multiple Coherence: A Somatosensory Evoked Response Detection Investigation

Abstract

In this work the performance of two techniques useful for detecting the somatosensory evoked potential (SEP), namely the Magnitude-Squared Coherence (MSC or Simple Coherence) and its multivariate version, the Multiple Coherence (MC), was compared. Electroencephalographic (EEG) signals during somatosensory stimulation were collected from forty adult volunteers without history of neurological pathology using the 10-20 International System. All leads were referenced to the earlobe average. The stimulation was carried out throughout current pulses (200 μs width) applied to the right posterior tibial nerve (motor threshold intensity level) at the rate of 5 Hz. The response detection was based on rejecting the null hypothesis of response absence (M = 100 epochs and significance level α = 0.05). The MSC was applied to the derivations [Cz], [Fz], [C3] and [C4], usually employed in the SEP recordings when bipolar derivations are used. The MC was applied to the pairs [Cz][Fz] and [C3][C4]. The results indicated that if two derivations are available, it should be better to use the MC applied to both leads than the MSC applied to each one.