Orbicularis oculi muscle activation during swallowing in humans

Intraoral trigeminal afferents elicit EMG activity from the lower facial muscle, orbicularis oris (OR) during swallowing. The upper facial muscles and especially orbicularis oculi (OC) were not previously known to be associated with deglutitional events. Nevertheless, given the large area of intraoral mucosa and teeth innervated by the trigeminal nerve afferents, a connection between OC motoneurons and deglutition may theoretically be expected, which we sought to evaluate in this study. Healthy controls were investigated for the possible synchronization of orbicularis OC and OR muscles during deglutition by the following methods: EMG activities were recorded during voluntary dry, 3-, 10-, 20-ml discrete wet swallowing, and sequential swallowing from a cup, concurrent with respiratory recording. A polygraphic recording was obtained from these muscles to determine whether they were synchronously activated during spontaneous swallowing. The polygraphic recording during spontaneous swallowing demonstrated that the OC and OR muscles were synchronously activated in all subjects. This synchronous activation was less prominent in voluntary discrete swallowing. It is proposed that this might be based on trigemino-solitarii-facial pathways with weaker connection to OC muscles. The synchronization of OC muscle activity with deglutition may be an evolutionary process that should be rudimentary in higher mammals including humans. The swallowing-induced cranial muscle activities could potentially explain some movement disorders, such as craniofacial dystonias.