Trigemino-cervical reflexes in normal subjects

Trigemino-cervical reflexes, recorded from the semispinalis capitis muscle (SCM) in the posterior neck, were studied in 35 healthy volunteers, in response to electrical stimulation of the supraorbital trigeminal nerve and glabellar tapping. Simultaneous responses evoked from the ipsilateral orbicularis oculi muscle (OOM) were also recorded i.e. blink reflexes. Electrical stimulation of the supraorbital nerve elicited a reflex response with a latency of about 50 ms from the ipsilateral SCM which was called C3. An early reflex response, which sometimes had two components with latencies of 18 ms and 35 ms, was elicited with glabellar taps. They were called C1 and C2 respectively. When CI and C2 were elicited with usual glabellar taps, C3 was suppressed. With electrical stimulation, suppression of C1 and C2 was noted, though C3 could easily be obtained. Electrophysiological characteristics of Cc (and C2) were compatible with an oligosynaptic, innocuous reflex, whereas C3 seemed to be multisynaptic and nociceptive in nature. A negative interaction between these two reflexes was observed.