Modification of the cervico-ocular reflex by canal plugging

Abstract

The cervico-ocular reflex (COR) has a low gain in normal animals. In this study, we determined whether COR gain increases were specific to the low/midband frequency range, which is the range over which the angular vestibulo-ocular reflex (aVOR) is compromised by plugging. The gain and phase of the yaw and pitch COR and aVOR were compared in normal monkeys and those with all six semicircular canals or only the lateral canal plugged. During experiments animals sat with the body fixed to a chair and the head fixed in space. The body was oscillated about body-yaw and body-pitch axes over a frequency range of 0.05-6 Hz, with amplitude <10 degrees. For normal animals, both yaw and pitch eye velocities were compensatory to the relative velocity of the head with respect to the body. The gains were 0.1-0.2 at frequencies below 1 Hz and decreased to zero as stimulus frequency increased above 1 Hz. Canal-plugged animals had COR gains close to 1.0 at low frequencies, decreasing to approximately 0.6 at 0.5 Hz and to 0.2 for stimulus frequencies above 3 Hz. The phase of eye velocity was 180 degrees relative to head-re-body velocity at frequencies below 0.5 Hz and shifted toward 270 degrees as frequencies were increased to 4 Hz. This study demonstrates that adaptation of COR gain is tuned to a frequency range at which the aVOR is compromised by the canal plugging.

Figure 1

(A, B) Gains of yaw and (C, D) pitch cervico-ocular reflex (COR) induced in (A, C) naïve cynomolgus and (B, D) rhesus monkeys.

Figure 2

Typical example of yaw eye velocities induced by body oscillation of a six canal-plugged animal (M9357) at frequencies of (A) ≈0.5 Hz and (B) ≈2.0 Hz. Vertical dotted lines in the eye-velocity traces are saccades that were marked for exclusion from analysis. Vertical double-headed arrows indicate that the peaks of yaw eye velocity are (A) 180° out of phase with peak yaw head-re-body velocity at 0.5 Hz, but (B) 180° out of phase with peak yaw head-re-body position at 2 Hz.

Figure 3

(A–C) Yaw cervico-ocular reflex (COR) (black symbols) and angular vestibulo-ocular reflex (aVOR) (gray symbols) obtained by rotation about spatial vertical axis in a six canal-plugged (M9357 and M17115) and lateral canal-plugged (M98078) animals. The black line is the fit of the COR gains with COR transfer function. The gray line is the fit of aVOR gains with a model-based aVOR transfer function. The dashed line is the summation of COR and aVOR transfer functions. (D–F) COR phases. The black line is the prediction of the COR phases based on the COR gain transfer function determined for each animal.

Figure 4

(A–C) Pitch cervico-ocular reflex (COR) (black symbols) and angular vestibule-ocular reflex (aVOR) (gray symbols) obtained by rotation about spatial vertical axis in a six canal-plugged (M9357 and M17115) and lateral canal-plugged (M98078) animals. The black line is the fit of COR gains with a first-order COR transfer function. The gray line is a fit of aVOR gains with model-based transfer function. The dashed line is the summation of COR and aVOR transfer functions. (D–F) COR phases. The black line is the prediction of the COR phases based on the COR gain transfer function determined for each animal.