Modulation of the trigeminofacial pathway during syllabic speech

Abstract

The human orofacial system is richly endowed with low threshold, slowly adapting mechanoreceptors that respond to self-generated movements and external loads. The functional linkage between these afferents and the recruitment of motor units in the lower face during the dynamics of speech is unknown. Mechanically evoked activity in the orbicularis oris muscles was studied in young human female adults (N=10) during a lip force recruitment task associated with the repetition of the nonsense speech utterance "ah-wah." This speech task involved the recruitment of perioral motor units against an elastic load. A skin contactor probe coupled to a servo-controlled linear motor delivered punctate ipsilateral mechanical inputs (25 ms duration, 1800 μm displacement) to the glabrous surface of the upper lip in order to index the modulation and specificity of the compound trigeminofacial response as a function of speech force recruitment threshold (Ft). Modulation of the early (Ft = 0.2N) and later (Ft = 1.0N) components of the evoked perioral response was found at the two force thresholds. Beginning at approximately 60 ms post-stimulus, a significant suppression response was found among lower lip EMG recording sites and its magnitude was greatest when the mechanical perturbation occurred during the early phase of lip force recruitment. Variation in the lip force trajectories was manifest by a greater difference in net interangle force associated with lip perturbations indexed to the early Ft. This was interpreted to reflect the operation of a feedforward mechanism which may play a more significant role during an evolving speech action. Thus, the application of servo-controlled mechanosensory inputs effectively indexed the excitability of the facial motor nucleus during production of a simple speech phrase. Future studies are needed to explore mechanisms of short-term adaptation and trigeminofacial modulation during propositional speech in health and disease.

An evaluation of the effectiveness of PROMPT therapy in improving speech production accuracy in six children with cerebral palsy

“…These fi ndings are supported by behavioural studies that indicate sensory augmentation can play a role in enhancing motor learning in general, particularly when stimuli are diffi cult to perceive (Atchy-Dalama, Peper, Zanone, & Beek, 2005). For example, researchers have demonstrated that modifi cations to the speech system through external perturbation (i.e., stretching of the facial skin at the lateral angle of the mouth) changes speech production (Estep & Barlow, 2007). Further, articulator coupling patterns will re-organize or compensate as a response to modifi cations/disruptions in articulator movements (Estep, 2009).…”

Cutaneous stimulation of the digits and lips evokes responses with different adaptation patterns in primary somatosensory cortex

“…Afferents in the lips respond not only to contact with environmental objects, but most frequently to contacts between lips, teeth, or tongue tip, which accompany movements associated with speech, chewing and swallowing. Tactile input from the upper and lower lips has been hypothesized to support feedback information during such motor tasks (Gracco and Abbs, 1985, 1988; Barlow, 1998; Estep and Barlow, 2007). Under this assumption, motor control of orofacial movements during speech and of digits during fine manipulation would be dependent on continuous monitoring of superficial and deep mechanoreceptive sensory input.…”

Trigeminofacial reflex: a means of detecting proximity to ophthalmic and maxillary divisions of the trigeminal nerve during surgery

“…5 However, it was Sindou et al 17,18 who first referred to the communication as the trigeminofacial reflex and implemented it in surgical localization, where they proposed an application for the phenomenon in thermorhizotomy for trigeminal neuralgia. Not only did they find that different facial muscle groups respond to stimulation of different divisions, but they also observed that these responses were reproducible.…”