Effect of experimental posterior temporalis muscle pain on human brainstem reflexes

Objective To study the modulation of jaw-stretch and blink reflexes by experimental posterior temporalis muscle pain. Methods Thirty healthy volunteers (15 males, 25.5±0.6 years and 15 females, 27.4±1.2 years) were included. Short-latency stretch reflex responses were evoked in the masseter and temporalis muscles by fast stretches (1 mm displacement, 10 ms ramp time) and the blink reflexes were evoked by painful electrical pulses (0.5 ms duration), delivered by a concentric electrode placed on the left lower forehead close to the supraorbital foramen before, during and 15 min after a period with experimentally induced muscle pain. Results The normalized peak-to-peak amplitude of the stretch reflex in the painful temporalis was significantly higher during pain in both males and females compared with pre- and post-pain conditions (P<0.004). The R2 root mean square (RMS) of the blink reflex decreased significantly during muscle pain as compared to the pre-pain (P<0.03) in both males and females. Conclusions The present results indicated that experimental posterior temporalis muscle pain facilitates the jaw-stretch reflex, whereas the nociceptive specific blink reflex is inhibited. Significance Present study suggested that these reflexes are suitable models for probing pontine and medullary pain processing.