Physiological oculo-auricular-facial-mandibular synkinesis elicited in humans by gaze deviations

Integrated motor behaviors involving ocular motion-associated movements of the head, neck, pinna, and parts of the face arecommonly seen in animals orienting to a visual target. A number of coordinated movements have also been observed in humansmaking rapid gaze shifts to horizontal extremes, which may be vestiges of these. Since such integrated mechanisms point to anonpathological coactivation of several anatomically separate cranial circuits in humans, it is important to see how the differentpairs of integrative motor behaviors with a common trigger (i.e., ocular motion) manifest in relation to one another. Here, we sys-tematically examined the pattern of eye movement-induced recruitment of multiple cranial muscles in humans. Simultaneousvideo-oculography and bilateral surface electromyograms of transverse auricular, temporalis, frontalis, and masseter muscleswere recorded in 15 healthy subjects (8 females; 29.3 ± 5.2 yr) while they made head-fixed, horizontal saccadic, pursuit, andoptokinetic eye movements. Potential chin laterotrusion linked to contractions of masticator muscles was captured with a jaw-fixed accelerometer. Ourfindings objectively show an orchestrated aural-facial-masticatory muscle response to a range of hori-zontal eye movements (prevalence of 21%–93%). These responses were most prominent during eccentric saccades. We furtherreveal distinctions between the various observed activation patterns in terms of their profile (transient or sustained), laterality(with respect to direction of gaze), and timing (with respect to saccade onset). Possible underlying neural substrates, their atavis-tic behavioral significance, and potential clinical applications for monitoring sensory attention and designing attention-directedhearing aids in the future are discussed. NEW & NOTEWORTHY: Healthy humans exhibit different combinations of nonpathological, synkinetic gaze-associated move-ments with aural, facial, and/or masticatory muscles during different types of voluntary and reflexive horizontal eye movements.The manifestations of these collective phenomena are strongest during large-scale horizontal saccades and accompanied by adetectable horizontal chin movement. Auricular muscle activations occur equally on both sides, whereas the activation of facialand masticatory muscles is predominantly ipsilateral (in regard to gaze direction)