The effect of Trigeminal Nerve Block on the Articulatory Emg Activity of Facial Muscles

Abstract

The effect of blocking trigeminal afferent fibres was studied with reference to the EMG activity of facial muscles during speech production. Normal-speaking subjects were investigated without and with mandibular anaesthesia, and patients with trigeminal neuralgia before and after blockade of the Gasserian ganglion. No audible difference was detected between the non-anaesthetized and the uni-or bilaterally anaesthetized. The most consistent and salient finding was a general increase in the amount of prespeech and background activity as well as, in particular, the amount of articulatory activity. This increase often appeared symmetrically on both sides even with unilateral anaesthesia and was localized to the muscles that are best adapted for the production of the speech sounds in question, while the cocontractive activity of the antagonistic muscles decreased. The increase was often associated with an earlier onset of articulatory activity. The context dependence of the EMG activity was obviously impaired for the production of vowels but not of consonants. These EMG observations are discussed in relation to previous reports by other authors on the effects of de-afferentation of the limb and intercostal musculature. It is concluded that the EMG changes observed after blocking of afferent activity in the trigeminal nerve cannot be explained by a disturbed peripheral closed-loop feedback, similar to the muscle spindle-gamma efferent system, which therefore does not seem to be crucial for adult speech production. However, the findings could be accounted for by a disturbed positional sense. To compensate for this disturbance, the control of articulatory activity, which is not normally conscious, may be referred to a higher level of the central nervous system. Such a more conscious motor control might explain the overshooting muscle activation and the lack of context dependence of the EMG activity.