Spatial and temporal response properties of secondary neurons that receive convergent input in vestibular nuclei of alert cats.

Responses to rotation in many vertical and horizontal planes were studied in electrically identified secondary vestibular neurons of alert cats. This report concerns secondary neurons that gave responses which could not be explained as due to a summation of semicircular canal inputs. These cells responded to sinusoidal rotation of the cat in any vertical plane, and response phase depended on the plane of rotation. The responses were modeled as the result of summation of two inputs that differed in their spatial orientations and dynamics. Response dynamics and a comparison of responses to vertical and horizontal rotations showed that some cells were sensitive to rotation with respect to gravity. Their responses both to gravity and horizontal rotations argue that these secondary neurons received convergent otolith and canal inputs. Some cells also had oculomotor related discharges and/or responded weakly to neck rotation.