It is known that sensory signals sustain the background discharge of the ascending reticular activating system (ARAS) which includes the noradrenergic locus coeruleus (LC) neurons and controls the level of attention and alertness. Moreover, LC neurons influence brain metabolic activity, gene expression and brain inflammatory processes. As a consequence of the sensory control of ARAS/LC, stimulation of a sensory channel may potential influence neuronal activity and trophic state all over the brain, supporting cognitive functions and exerting a neuroprotective action. On the other hand, an imbalance of the same input on the two sides may lead to an asymmetric hemispheric excitability, leading to an impairment in cognitive functions. Among the inputs that may drive LC neurons and ARAS, those arising from the trigeminal region, from visceral organs and, possibly, from the vestibular system seem to be particularly relevant in regulating their activity. The trigeminal, visceral and vestibular control of ARAS/LC activity may explain why these input signals: (1) affect sensorimotor and cognitive functions which are not directly related to their specific informational content; and (2) are effective in relieving the symptoms of some brain pathologies, thus prompting peripheral activation of these input systems as a complementary approach for the treatment of cognitive impairments and neurodegenerative disorders.

Cerebellar modules process afferent information and deliver outputs relevant for both reflex and voluntary movements. The response of cerebellar modules to a given input depends on the whole array of...

Starting from a survey of current ideas on the role of the cerebellum in sensorimotor transformations, the present review summarizes the results of recent experiments showing that (a) somatosensory...

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.

Sensorimotor trigeminal unbalance modulates pupil size

Objective To verify whether the direction of head tilt coded by the population response of Purkinje (P) cells located in the cerebellar anterior vermis is modified by the relative position of the body with respect to the head. Material and Methods In decerebrate cats, the responses of P cells to wobble of the whole animal were analyzed in order to compute the response vectors of the same cells to the labyrinthine input. These response vectors were used to evaluate the population response (vector) of all the recorded neurons to head tilt in specific directions. Results When the head was aligned with the body, the direction of the population vector closely corresponded to that of head tilt. A 30° body-to-head rotation to the left or right around a C1–C2 vertical axis modified the response vectors of most of the recorded neurons, leading to reciprocal deviations of the population vector from the direction of head tilt of ≈30°. Conclusion We propose that information from neck receptors regulates the convergence of labyrinthine signals with different spatial and temporal properties on corticocerebellar units, thus allowing the P-cell population to code the direction of body tilt.