Quantitative analysis of reflex inhibition in single motor units in human masseter muscle: effects of stimulus intensity.
Inhibitory reflex responses to electrical stimulation of the mental nerve were studied in recordings from single motor units (SMU) in the human masseter muscle. A new analytical technique for spike train data was used. Electrical stimuli were delivered to the mental nerve when the SMU fired with two consecutive inter-spike intervals (ISIs) within the range of 90 ms to 110 ms. Stimuli were delivered with increasing stimulus delays after the preceding SMU action potential (AP). Sham, non-painful, and painful stimulus intensities were applied. The post-stimulus firing probability of the SMU was progressively decreased among the three conditions. Analysis of the relation between stimulus delays and ISI for the first post-stimulus APs revealed a linear relation which was shifted upward, and the slope was increased with increasing stimulus intensity. This may be explained by a differential effect of the increasing stimulus intensity on the duration and amplitude of the inhibitory post-synaptic potential. The methods used in the present study provide a useful means of quantifying the effects of motoneuron excitability in detail.
Graven-Nielsen
T
T
Center for Sensory-Motor Interaction, Laboratory for Experimental Pain Research, Aalborg University, Fredrik Bajers Vej 7D-3, DK-9220 Aalborg E, Denmark. tgn@miba.auc.dk
Svensson
P
P
McMillan
A S
AS
Arendt-Nielsen
L
L
D000328:Adult; D004558:Electric Stimulation; D004566:Electrodes; D004576:Electromyography; D006801:Humans; D008297:Male; D008406:Masseter Muscle / Q000166:cytology / Q000294:innervation / Q000502:physiology*; D009046:Motor Neurons / Q000502:physiology*; D010146:Pain / Q000503:physiopathology; D012018:Reflex / Q000502:physiology*; D012044:Regression Analysis