Short-Term Effects of Chewing on Task Performance and Task-Induced Mydriasis: Trigeminal Influence on the Arousal Systems

Abstract

Trigeminal input to the ascending activating system is important for the maintenance of arousal and may affect the discharge of the noradrenergic neurons of the locus coeruleus (LC), whose activity influences both vigilance state and pupil size, inducing mydriasis. For this reason, pupil size evaluation is now considered an indicator of LC activity. Since mastication activates trigeminal afferent neurons, the aims of the present study, conducted on healthy adult participants, were to investigate whether chewing a bolus of different hardness may: (1) differentially affect the performance on a cognitive task (consisting in the retrieval of specific target numbers within numerical matrices) and (2) increase the dilatation of the pupil (mydriasis) induced by a haptic task, suggesting a change in LC activation. Results show that chewing significantly increased both the velocity of number retrieval (without affecting the number of errors) and the mydriasis associated with the haptic task, whereas simple task repetition did not modify either retrieval or mydriasis. Handgrip exercise, instead, significantly decreased both parameters. Effects were significantly stronger and longer lasting when subjects chewed hard pellets. Finally, chewing-induced improvements in performance and changes in mydriasis were positively correlated, which suggests that trigeminal signals enhanced by chewing may boost the cognitive performance by increasing LC activity.

Trigeminal, Visceral and Vestibular Inputs May Improve Cognitive Functions by Acting through the Locus Coeruleus and the Ascending Reticular Activating System: A New Hypothesis

“…So, orofacial input is particularly effective in enhancing arousal, thus boosting performance. In fact, 2 min of chewing a hard pellet may boost performance and task-induced mydriasis, while a bilateral handgrip exercises of the same duration do not (Tramonti Fantozzi et al, 2017 ). These data are consistent with the observation that, in the encephale isolé preparations, where ARAS and LC have been disconnected from the spinal cord, an additional lesion of the trigeminal, but not of the other cranial nerves afferents, triggers the transition of the desynchronized EEG activity towards a synchronized sleeping pattern (Roger et al, 1956 ).…”

“…Since the LC is implicated in AD initial stages, stimulation of trigeminal proprioceptive afferents, which could be electrically coupled to LC neurons (Fujita et al, 2012 ; see however Tramonti Fantozzi et al, 2017 ), could rescue their activity and trophic condition. Indeed, chewing helps to maintain cognitive functions while masticator deficiency is associated with development of dementia (Teixeira et al, 2014 ).…”

Standard Correction of Vision Worsens EMG Activity of Pericranial Muscles in Chronic TMD Subjects

“…Voluntary teeth clenching and rubber mastication in humans can modify pupil dynamics, probably indirectly, via stimulation of the locus coeruleus and the ascending systems of arousal [59]. Alterations in occlusal status or chronic pain disorders of the trigeminal region are associated with dysregulation of arousal-related systems [42,60].…”

Linear and non linear measures of pupil size as a function of hypnotizability

“…Before the experimental session, participants completed the State Anxiety Inventory (STAI-X) 64 to ascertain the absence of basal differences in anxiety which could bias the pupil response to the procedure 77 . Then, they sat in a comfortable armchair in a sound attenuated room with constant temperature (20°) and luminance (neon light illumination) and were invited to relax at their best and to avoid the contact between teeth arches to prevent trigeminal stimulation possibly leading to LC activation 78 . ECG, Skin Conductance (SC) and the right pupil diameter were recorded during a simple relaxation session 60 lasting 6 min, after 5 min of familiarization with the experimental setting .…”