Response of semicircular canal dependent units in vestibular nuclei to rotation of a linear acceleration vector without angular acceleration

Abstract

SUMAARY1. Recent experiments have shown that rotation of a linear acceleration vector round the head can generate involuntary ocular nystagmus in the absence of angular acceleration. The present experiments examine the suggestion that adequate stimulation of the semicircular canals may contribute to this response.2. Decerebrate cats were located in a stereotaxic device on a platform, slung from four parallel cables, which could be driven smoothly round a circular orbit without inducing significant angular movement of the platform. This Parallel Swing Rotation (PSR) generated a centripetal acceleration of 4-4 m/sec2 which rotated round the head at 052 rev/sec.3. The discharge frequency of specifically lateral canal-dependent neural units in the vestibular nuclei of cats was recorded during PSR to right and left, and in the absence of motion. The dynamic responses to purely angular motion were also examined on a servo-driven turntable.4. Without exception all proven canal-dependent cells examined (twenty-nine cells in nine cats) were more active during PSR in the direction of endolymph circulation assessed to be excitatory to the unit, than during PSR in the opposite direction.5. The observed changes in discharge frequency are assessed to have been of a magnitude appropriate for the generation of the involuntary oculomotor response induced by the same stimulus in the intact animal.6. The findings suggest that a linear acceleration vector which rotates in the plane of the lateral semicircular canals can be an adequate stimulus

Two-dimensional coding of linear acceleration and the angular velocity sensitivity of the otolith system

“…In contrast to the sinusoidal responses of vestibular nuclei neurons reported during stimulation with a rotating linear acceleration vector (Melvill Jones and Milsum, 1969;Schor et al 1984;Chan et al 1987), Benson et al (1970) showed that some vestibular nuclei neurons responding exclusively to horizontal canal stimulation had different mean firing rates at rest and during constant velocity CW and CCW rotation of a linear acceleration vector around the animal's horizontal plane. The generation of these responses involves an additional computational step beyond the output of the "two-dimensional" neurons described here.…”

“…As explained above, the response of "two-dimensdional" neurons to OVAR is sinusoidal and the information regarding the rotational velocity is carried in the difference between their amplitude modulation during CW and CCW rotations. An additional nonlinear step is necessary to "rectify" these sinusoidal responses and produce the observed steady-state change in the neuronal firing rate during OVAR (Benson et al 1970). The accompanying paper (Angelaki 1992b) suggests a biologically plausible mechanism for this "rectification".…”

Detection of rotating gravity signals

“…Vestibular nuclei neurons that change their mean firing rate during constant velocity rotation of a linear acceleration vector have been reported by Benson et al (1970) and recently by Reisine and Raphan (1992). Chan et al (1987) observed periodic modulations in the firing rates of vestibular nuclei neurons during OVAR at 1.75~ (0.005 Hz), however, no changes in the mean firing rates were reported.…”

Nystagmus Responses during Rotation about a Tilted Axis,

“…None of these hypc..eses has, as yet, received direct experimental verification; so, the issue is unresolved. However, a relevant observation was provided by Benson et al (6) when they recorded action potentials from neurons in the medial vestibular nucleus of the cat. These units had been rigorously diagnosed as "canal-dependent," yet they also responded to a rotating linear acceleration vector.…”