A fully automated system for the evaluation of masseter silent periods

Exteroceptive suppression of masseter muscle activity, 'masseter inhibitory reflex', comprises one or 2 silent periods (SP1 and SP2) interrupting the voluntary activation. The main problem when evaluating exteroceptive suppression is the lack of an objective and precise measure for the onset and end of the silent period which so far has not been overcome by various automated systems. We describe a new fully automated system for determining the onset and end of the masseter silent period. The decision approach is essentially based upon deterministic properties of median filters which are used to partition the local variances of the EMG traces into constant segments and edges between them. The system was tested in 13 healthy volunteers with 2 subjects tested serially 10 times each to get estimates of the inter- and intra-individual variability. The performance of the system compared favourably to that of a simpler approach and to earlier results from our laboratory. The inter-individual variability of the SP1 onset was 17 times smaller than when based on a subjective decision process.