Tibial nerve somatosensory evoked response detection using uni and multivariate coherence
This work aims at comparing the capability of two Objective Response Detection techniques, the Magnitude-Squared Coherence (MSC or Ordinary Coherence) and its multivariate extension, the Multiple Coherence (MC), of detecting the somatosensory evoked response. Electroencephalographic (EEG) signals were collected during somatosensory stimulation from forty adult volunteers without history of neurological disease and with normal somatosensory evoked potential (SEP), using the 10-20 International System. All leads were referenced to the earlobe average. Current pulses with 200?s of duration were applied to the right posterior tibial nerve at the motor threshold intensity level (the lowest intensity able to produce hallux oscillations) at the rate of 5Hz. The MSC was applied to the derivations [Cz], [Fz], [C3] and [C4]  commonly used for tibial nerve SEP recordings with bipolar derivations  and the MC was applied to the pairs [Cz][Fz] and [C3][C4]. Both estimates (MC and MSC) were calculated with M=100 and 500 epochs and the response detection was based on rejecting the null hypothesis of response absence, which is achieved when the estimates exceed the critical value (detection threshold) calculated for a given significance level (?=0.05). The results showed that if two leads are available, the application of the MC is better than the MSC applied to each lead individually.
tibial nerve ordinary coherence multiple coherence (mc) somatosensory evoked potential magnitude-squared coherence (msc) objective response detection (ord)