This two-year award is on the function of the vestibular system of the inner ear, used for balance. The semicircular canals of the vestibular system are fluid-filled ducts in the head. When the head is rotated, the fluid in each canal shifts, and stimulates mechanosensory cells called hair cells. The activity of these cells then stimulates the neurons (nerve cells) of the vestibular nerve to the brain. The neurons are sensitive over a very wide frequency range of head movements, and also show some decrease in activity, or adaptation, to high frequency or high intensity stimuli. This project will test the responses of the canal nerves for stimuli representing various frequencies of head oscillations (from 0.01 per second to nearly 100 per second). This wide stimulus range will establish the limits of current bioengineering models of the vestibular syste in a way which has only been touched on by other experiments. The wide range of stimuli is important to many animals, but pigeons provide an excellent model because they receive very low frequencies of swaying perches in trees, to the very high frequencies of air turbulence in fast flight. Both rotational stimulation and direct mechanical stimulation of the canals will be used, and nerve activity recorded. The mathematical transfer function that relates nerve sensitivity to stimulus frequency will be determined, and the degree of adaptation across frequencies will be measured. The results will allow determination of an important parameter in vestibular mechanics, the value of the short time constant, which has not yet been established for warm- blooded vertebrates. This work is a novel approach that has some technical challenges, but should have high impact on a sensory system that is not yet well understood.
