Sensorimotor trigeminal unbalance modulates pupil size

We studied whether the patients affected by Temporo-Mandibular Disorder (TMD) showing asymmetric electromyographic (EMG) activity of masticatory muscles display asymmetries also in the pupils size in order to detect a possible tonic trigeminal control on autonomic centres. In 30 pain free TMD patients, we found a highly significant, positive correlation between left-right differences in EMG and pupils size. The asymmetry in the pupils size was likely induced by the asymmetric sensorimotor signals arising from the oro-facial region, as the pupils asymmetry decreased significantly after application of a cusp bite. Moreover, cusp bite wearing bilaterally increased the mydriasis induced by performing haptic tasks. Finally, unbalancing the occlusion by a precontact increased the diameter of the ipsilateral pupil and abolished the mydriasis induced by haptic tasks. In conclusion, trigeminal sensorimotor signals may exert a tonic control on autonomic structures regulating the pupils size at rest and during haptic tasks. Since task-associated mydriasis is correlated with task performance and is strictly proportional to the phasic release of noradrenaline at cerebral cortical level, present findings suggest that unbalanced trigeminal activity influences brain processes not directly related to the orofacial region.