The goal of the proposed research is to understand the vestibulo-cervical reflex, also called the vestibulocollic reflex (VCR), and its relation to the vestibulo-ocular reflex (VOR) and vestibulo-spinal postural reflexes. The neuronal circuitry of vestibular reflexes receives vestibular input from the semicircular canals and otoliths, and coordinates muscle contractions throughout the body. When vestibular reflexes are disabled, vision is badly blurred, the head wobbles rapidly and uncontrollably, and falls are likely. Thus, one vestibular reflex function is to maintain body, head, and eye stability. Head and body righting reflexes are also disrupted by interruption of vestibular signals, suggesting that another reflex function is righting the head and body to return to the usual upright posture. Studies are planned to examine the interaction of the VCR with the VOR, and to record the activity of individual neurons that send axons to the motor neurons that control the VCR and VOR. The proposed research in cats and mice has two experimental aims: 1. Record the activity of individual vestibulo-cervical neurons (VC neurons) whose axons are electrically activated antidromically from the vicinity of the descending medial vestibulospinal tract to the cervical motor neurons, vestibulo-ocular neurons (VO neurons) whose axons are electrically activated antidromically from the vicinity of the extraocular motor neurons, and vestibulo-oculo-cervical neurons (VOC neurons) activated from both sites. Compare the signals carried by the three classes of neurons during the reflex tests of aim 2. 2. Document VCR and VOR independence or interaction, by recording behaviors and cervical muscle electromyographic activity to test the ideas that the VCR over-rides the VOR for body righting, and that the VCR uses signals known to be constructed by the brain for use by the VOR, head angular velocity storage and velocity estimation. This research will expand our knowledge of sensory-motor neuronal systems and vestibular reflexes. Results may be relevant to treatment of otologic, neurological, or neuromuscular disease such as torticollis, vertigo, and cerebellar and oculomotor disorders, and help us understand neurological injury and disease in general.
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