A new method for eliciting and studying H-reflexes in the human masseter

A non-invasive method is presented for transmuscular stimulation of the masseteric nerve, using a frame to apply a cathode to the mandibular notch and an anode to the inside of the mouth. The H-reflex response was recorded using surface, macro and single motor-unit (SMU) electromyography (EMG) from the masseter. The latency of the reflex response representing the H-reflex in SMUs was determined from the cumulative sum of the peristimulus time histogram. This latency was then corrected using a spike-trigger averaging technique, where the SMU spikes were used as triggers and the macro EMG recording as the source. SMU latencies for the H-reflex in masseter were in the range 5.9–8.8 msec, whereas H-reflex latencies for surface EMG varied between 5.4 and 6.4 msec.