Abstract
Chewing improves cognitive performance, which is impaired in subjects showing an asymmetry in electromyographic (EMG) masseter activity during clenching. In these subjects, the simultaneous presence of an asymmetry in pupil size (anisocoria) at rest indicates an imbalance in Ascending Reticular Activating System (ARAS) influencing arousal and pupil size. The aim of the present study was to verify whether a trigeminal EMG asymmetry may bias the stimulating effect of chewing on cognition. Cognitive performance and pupil size at rest were recorded before and after 1 min of unilateral chewing in 20 subjects with anisocoria, showing an EMG asymmetry during clenching. Unilateral chewing stimulated performance mainly when it occurred on the side of lower EMG activity (and smaller pupil size). Following chewing on the hypotonic side, changes in cognitive performance were negatively and positively correlated with those in anisocoria and pupil size, respectively. We propose that, following chewing on the hypotonic side, the arousing effects of trigeminal stimulation on performance are enhanced by a rebalancing of ARAS structures. At variance, following chewing on the hypertonic side, the arousing effect of trigeminal stimulation could be partially or completely prevented by the simultaneous increase in ARAS imbalance.
Highlights
Recent investigations have shown how chewing can exert a stimulating effect on cognitive performance
The results of the present experiments highlight only minor differences between right and left dominant subjects, while indicate that the presence of an asymmetry in EMG activity during clenching constrains the stimulating effects of chewing on performance, which occur mainly when mastication is performed on the hypotonic side
These results could be attributed to a refractoriness of ARAS structures on the hypertonic side to sensorimotor trigeminal activation, or else to a change in the ARAS imbalance which is detrimental for cognitive performance and is reduced following chewing on the hypotonic side
Summary
Recent investigations have shown how chewing can exert a stimulating effect on cognitive performance. Shortening of reaction times and latencies of stimulus-triggered evoked potentials are observed (Sakamoto et al, 2009; Hirano and Onozuka, 2014). The decrease in reaction time (Hirano and Onozuka, 2014) and the enhancement of short-term memory processing (Hirano et al, 2008) induced by chewing are coupled to an increase in the blood-oxygenlevel dependent (BOLD) signal in those brain regions activated by a cognitive task. Stimulation of cognitive performance elicited by chewing can last for a period of 15–20 min (Onyper et al, 2011) and even more, when hard pellet is chewed (Tramonti Fantozzi et al, 2017).
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