Vestibular contribution to the orientation of cervico-ocular reflex in rabbit

In the rabbit the cervico-ocular reflex (COR) helps to maintain the gaze stability during passive head displacements, by increasing the gain and decreasing the phase lead of low frequency vestibular responses and by diminishing in amplitude the anticompensatory vestibular fast phases. These cervical influences appear only for horizontal stimulations, while they are scarce or absent in the vertical and sagittal planes. Ocular responses to horizontal body displacements are oriented in the horizontal plane and remain in the same plane when the head is statically pitched at various degrees, in spite of the directional changes in the extraocular muscle (EOM) lines of force with respect to space. Tension recordings from the EOMs show that the oculomotor system is differently activated depending upon the degree of head inclination. This change in the EOM activation is not observed when the body, instead of the head, is pitched. Furthermore, after bilateral labyrinthectomy (BL) the cervico-ocular responses lose their appropriate directionality. It is concluded that the information for determining the plane of the eye movements during cervical stimulations does not originate from the neck proprioception but is provided by the otolithic receptors.