OWN - Quintessenz Verlags-GmbH CI - Copyright Quintessenz Verlags-GmbH OCI - Copyright Quintessenz Verlags-GmbH TA - J Orofac Pain JT - Journal of Oral & Facial Pain and Headache IS - 2333-0376 (Electronic) IS - 2333-0384 (Print) IP - 1 VI - 34 PST - ppublish DP - 2020 PG - 40-52 LA - en TI - Reorganization of Masseter and Temporalis Muscle Single Motor Unit Activity During Experimental Masseter Muscle Pain FAU - Ferreira, Polyana Moura AU - Ferreira P FAU - Sandoval, Isbel AU - Sandoval I FAU - Whittle, Terry AU - Whittle T FAU - Mojaver, Yalda Nozad AU - Mojaver Y FAU - Murray, Greg M. AU - Murray G CN - OT - electromyography OT - hypertonic OT - isometric contraction OT - masticatory muscles OT - saline solution AB - Aims: To test the hypothesis that experimental noxious stimulation of the right masseter muscle results in a reorganization of motor unit activity within the right temporalis and right masseter muscles during jaw closing tasks. Methods: A total of 20 healthy participants received hypertonic saline (5% sodium chloride) infusion into the right masseter muscle, and pain intensity was maintained at 40-60/100 mm on a visual analog scale. Standardized isometric biting tasks were performed with an intraoral force transducer while single motor units (SMUs) were recorded from the right masseter and temporalis muscles. Tasks were repeated in four blocks: block 1 (baseline 1), block 2 (hypertonic saline [HS] infusion or isotonic saline [IS] infusion), block 3 (infusion of the other solution), and block 4 (baseline 2). The occurrences of SMUs were tabulated across blocks. Statistical significance was considered to be P < .05. Results: There were no significant effects of block on the tasks. A total of 83 SMUs were discriminated in the temporalis and 58 in the masseter. For the comparison between HS and IS across tasks, the occurrences of 74.6% to 82.8% of SMUs were unchanged (70.2% to 94.3% for masseter), while during HS, 10.3% to 17.1% of SMUs were recruited (0% to 12.8%, masseter) and 6.9% to 12.7% were de-recruited (5.7% to 17%, masseter). Conclusion: The present findings suggest that most biting-task-related jaw muscle SMUs remain active during experimental muscle noxious stimulation. There was some evidence in both the anterior temporalis and masseter muscles for motor unit recruitment and de-recruitment consistent with a motor unit reorganization during experimental pain. AID - 851534