Journal of Neurophysiology, Vol 60, Issue 5 1739-1752, Copyright © 1988 by APS
Yaw direction neurons in the cat inferior olive
F. R. Robinson, M. O. Fraser, J. R. Hollerman and D. L. Tomko
Department of Physiology, University of Pittsburgh School of Medicine, Pennsylvania 15261.
1. Single units that responded to yaw rotation were recorded
extracellularly in the caudal inferior olive (IO) of
barbiturate-anesthetized cats. Of 276 neurons, 55 responded reliably to
yaw, and extensive quantitative data were recorded from 25. 2. No
yaw-sensitive IO neuron responded to somatosensory or auditory stimuli but
two responded, though unreliably, to flash. 3. Yaw-sensitive IO cells fired
at low (1-4 spikes/s), irregular rates during one direction of rotation.
Though cells responded reliably during yaw, firing rates varied
considerably from cycle to cycle. Rotation speed and acceleration were not
represented in any cell's firing rate. 4. Eighty five percent (47/55) of
yaw-sensitive cells fired during contralateral rotation, 9% (5/55) during
ipsilateral rotation, and 6% (3/55) fired from late in the ipsilateral
phase of a sinusoidal oscillation to the middle of the contralateral phase.
5. Responses were tested to 0.1-Hz sinusoidal yaw oscillations with a range
of peak angular velocities (1-200 degrees/s). Thresholds were not sharp
because of the cycle to cycle variability in response rates but were
estimated using averaged responses. The peak rate of the most sensitive
cell was driven to criterion (2 SD above spontaneous rate) by an
oscillation with a peak velocity of 1 degrees/s. Other cells reached
criterion between 5 and 50 degrees/s. 6. Sinusoidal oscillation at all
frequencies tested (0.01-0.5 Hz) elicited approximately the same firing
rates. Even at 0.01 Hz cells responded well. Responses lagged acceleration
by approximately 25 degrees at 0.01 Hz and shifted to later parts of the
cycle as frequency increased so that firing lagged acceleration by
approximately 200 degrees at 0.5 Hz. 7. Histological reconstruction showed
that yaw-sensitive neurons were recorded in olivary subnucleus beta (N
beta), the dorsal cap of Kooy (DC), the posterior medial region of the
medial accessory division of the inferior olive (MAO), and in the
medial-lateral center of the caudal MAO. 8. Yaw-sensitive neurons in the
inferior olive provide a signal to the cerebellum that indicates the
direction of passive rotation over a wide range of velocity and
acceleration. The signal from individual neurons does not reliably encode
either rotation velocity or acceleration. Yaw-sensitive IO neurons are
therefore unlike other central vestibular neurons but are similar to
somatosensory IO cells which signal the presence, but not the intensity of
a stimulus.
