Trigeminal responses evoked by painful electrical stimulation.

Trigeminal sensory and motor responses to high-intensity electrical stimuli were studied in 10 healthy male subjects. During contraction at 10% of maximal bite force, late exteroceptive suppression periods assessed by EMG and bite force from masseter muscles were recorded together with evoked vertex potentials. Electrical stimuli were either delivered as 1 ms single pulses or as 21 ms (5 x 1 ms, 200 Hz) train pulses at two different intensities above the pain threshold. Three different perioral regions were stimulated in random order. The duration of the masseter suppression period was significantly longer and its latency significantly shorter at higher stimulus intensities whereas the amplitude of the evoked vertex potentials remained unchanged. Both the evoked potentials and the exteroceptive suppression period in the masseter muscle differed significantly between stimulation at the three perioral regions. The present results from combined measurements of sensory and motor responses in the trigeminal system may be explained by the function of trigeminal polysynaptic reflex circuits and the central cerebral processing of afferent inputs.