Journal of Neurophysiology, Vol 42, Issue 5 1479-1493, Copyright © 1979 by APS
Statoacoustic properties of utricular afferents
R. Budelli and O. Macadar
1. We classified the utricular afferents on the basis of their spontaneous
acitivity and responses to tilts and vibrations. 2. Type I afferents fire
spontaneously in a regular pattern; their responses to tilts consist of a
phasic-tonic change in firing rate. They may respond to vibrations by
increasing or decreasing their rate and show no adaptation. 3. The
spontaneous activity and the responses to tilts of type II are similar to
those observed in type I afferents. The differences become apparent when
the preparation is subjected to a vibrational stimulus, since type II
neurons increase their firing rate regardless of the stimulus frequency and
show adaptation. 4. Type III neurons have no spontaneous activity. They
respond to tilts by firing during the transition from one position to the
other. They respond to a vibrational stimulus with maintained firing and
show no adaptation. 5. We studied the dynamic responses of each type of
neuron. We used sensitivity curves for the study of type III afferents and
proposed a statistical method to define gain curves for the study of the
other types. 6. The gain curves generated by type I neurons reach their
maximum at frequencies of stimulation close to the spontaneous rate of
firing. 7. In the gain curves of type II afferents the maximum corresponds
to frequencies higher than their spontaneous activity. 8. Sensitivity
curves and gain curves give similar results for type III fibers. The
sensitivity curves of these afferents were classified into four subtypes.
9. We studied the responses of the three types of afferents to bursts of
sinusoidal vibrations. 10. We concluded that the properties of types I and
II fibers are fit to carry information about movements and position of the
head, but also transmit acoustical information. Type III fibers are more
adapted to provide information about acoustical stimuli, but can also
convey information about head movements.
