Mechanisms underlying the effects of remote noxious stimulation and mental activities on exteroceptive jaw reflexes in man.
Successive inhibitory, excitatory, inhibitory and excitatory reflexes (the Q, R, S and T waves of the post-stimulus electromyographic complex (PSEC)), evoked by applying non-painful taps to an incisor tooth, were recorded from the jaw-closing muscles of 15 subjects. The effects on these reflexes of the subjects undertaking mental exercises (MEx) in the form of arithmetic calculations were compared with those of remote noxious stimulation (RNS; application of 3 degrees C to a hand). This was done to investigate whether the previously established effects of RNS were likely to be related to a change in the subject's mental state and/or to direct nociceptive mechanisms. Both MEx and RNS caused increases in EMG activity around the Q-R and S-T transitions of the PSEC, which resulted principally from shortenings of the inhibitory Q and S waves. Reducing the intensity of the tap stimuli, which mimicked condition-induced disinhibition, caused shortenings of the inhibitory waves at latencies similar to the shortenings induced by MEx or RNS. The magnitude of the RNS-induced effect on the ST segment of the PSEC was greater (P<0.01) than that on the QR segment. By contrast, MEx induced similar effects on both segments. Regression analyses were performed for the relationship between condition-induced changes in amplitude of the excitatory waves and their control amplitudes. These analyses were performed to reveal any condition-induced inhibition or facilitation of the tap-induced influences on the motoneurons. Overall, the evidence suggested that: (1) mental exercise induced a similar degree of inhibition of the two tap-induced inhibitory jaw reflexes and a facilitation of the excitatory ones, and (2) remote noxious stimulation induced an inhibition of the second tap-induced inhibitory reflex which was greater than that of the first one, and an inhibition of the first excitatory reflex. Thus, although factors related to altered mental activity could play a role in the modulation of jaw reflexes by RNS, the differences between the effects of MEx and RNS suggest that alternative or complementary mechanisms are also likely to be involved.
van der Glas
H W
HW
Department of Oral-Maxillofacial Surgery, Prosthodontics and Special Dental Care, Utrecht University, P.O. Box 80.037, 3508 TA, Utrecht, The Netherlands. h.w.vanderglas@med.uu.nl
Cadden
S W
SW
van der Bilt
A
A
D000328:Adult; D003080:Cold Temperature; D004576:Electromyography; D005260:Female; D006225:Hand / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008410:Masticatory Muscles / Q000502:physiology*; D008433:Mathematics; D008606:Mental Processes / Q000502:physiology*; D010146:Pain / Q000503:physiopathology*; D010812:Physical Stimulation; D011930:Reaction Time; D012018:Reflex / Q000502:physiology*; D012044:Regression Analysis