Abstract
Several studies have demonstrated that chewing can be regarded as a preventive measure for cognitive impairment, whereas masticatory deficiency, associated with soft-diet feeding, is a risk factor for the development of dementia. At present the link between orofacial sensorimotor activity and cognitive functions is unknown. In subjects with unilateral molar loss we have shown asymmetries in both pupil size and masticatory muscles electromyographic (EMG) activity during clenching: the molar less side was characterized by a lower EMG activity and a smaller pupil. Since implant-prostheses, greatly reduced both the asymmetry in EMG activity and in pupil’s size, trigeminal unbalance, leading to unbalance in the activity of the Locus Coeruleus (LC), may be responsible for the pupil’s asymmetry. According to the findings obtained in animal models, we propose that the different activity of the right and left LC may induce an asymmetry in brain activity, thus leading to cognitive impairment. According to this hypothesis, prostheses improved the performance in a complex sensorimotor task and increased the mydriasis associated with haptic tasks. In conclusion, the present study indicates that the implant-prosthesis therapy, which reduces the unbalance of trigeminal proprioceptive afferents and the asymmetry in pupil’s size, may improve arousal, boosting performance in a complex sensorimotor task.
Highlights
Previous studies reported that mastication improves cognitive processing speed [1], alertness [2], attention [3], intelligence [4], as well as reaction time [5,6], event-related potentials latencies [7] and cerebral blood oxygen-dependent (Bold) signal [6]
All the subjects analysed in the CROWN OFF condition showed asymmetries in EMG activity of masseter muscles during biting (Fig 4A) and in the basal pupil size (Fig 4B)
The present findings indicate that, in subjects deprived unilaterally of the first and second molar, an asymmetric EMG activity of masticatory muscles develops when the arches are in contact
Summary
Previous studies reported that mastication improves cognitive processing speed [1], alertness [2], attention [3], intelligence [4], as well as reaction time [5,6], event-related potentials latencies [7] and cerebral blood oxygen-dependent (Bold) signal [6]. It has been proposed that chewing may enhances arousal and modulate cognitive functions [7] by enhancing the activity of Ascending Reticular Activating System [8]. In additions to these short-term effects on performance, it has been suggested that the cerebral cortex activity elicited by mastication may lead to long term effects on the cerebral nervous system and be helpful in preventing degradation of brain functions [9,10,11]. Epidemiological studies have reported that tooth loss before 35 years of age was a significant risk factor for dementia or Alzheimer Disease [12,13].
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