Abstract
The effect of unilateral sound stimulation (95 dB(A), 490 Hz) on antigravity muscles subserving postural balance, and on neck and forearm muscles was recorded in a patient with sound-induced oscillopsia, vertigo, and postural imbalance (otolithic Tullio phenomenon) using surface EMG electrodes; postural sway was measured while the patient stood upright with his eyes closed on a Kistler platform. The tibialis anterior and gastrocnemius muscles of the ipsilateral leg were coactivated at latencies as short as 47 ms (mean 58 ± 10 ms), with a weaker activation of the contralateral lower leg muscles following about 10 ms later. Neck muscles, triceps brachii, and forearm extensor muscles ipsilateral to the stimulated ear were activated at latencies as long as those of the lower leg muscles or often longer. Changes in posture, e.g. turning the head in either direction, balancing on one foot, and sitting or resting supine, as well as visual input modulated these early motor responses. They are thus of functional significance for counterregulating body perturbations and maintaining equilibrium in man. We conclude that otolithic input contributes directly to the control of posture and gait by fast descending pathways.
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