THE INFLUENCE OF ATTENTIONAL FACTORS ON SHORT-LATENCY AND LONG-LATENCY JAW REFLEXES IN MAN

Reflexes evoked by applying non-painful taps to an incisor tooth were recorded bilaterally from the jaw-closing masseter and temporal muscle s of 21 humans. A series of inhibitory, excitatory, inhibitory and exc itatory waves (the Q, R, S and T waves) appeared in full-wave rectifie d and averaged post-stimulus electromyograms. These reflex responses w ere effected by the participants' levels of attention. When they under took mental exercises in the form of arithmetic calculations, increase s in electromyographic activity were found around the transitions betw een the Q and R and the S and T waves. These increases involved princi pally a shortening of the inhibitory Q and S waves. There was no signi ficant difference between the occurrence of these effects in the QR an d ST segments. However, the effects were seen more commonly when the r eflexes were evoked by hard (7.4 mN.s) as opposed to soft (3.4 mN.s) t aps. It is concluded that, in man, attentional factors can modulate bo th short- and long-latency jaw reflexes, particularly when these are e voked by higher-threshold afferent nerves. Copyright (C) 1997 Elsevier Science Ltd.