Horizontal canal input to upper cervical commissural neurons.

We studied in decerebrate, paralyzed cats, the effect of sinusoidal yaw rotation on upper cervical commissural neurons. The activity of some neurons was modulated by this stimulus, and they were classified as receiving input from the horizontal semicircular canal. The responses, which were mainly type II, were well correlated with the velocity of the stimulus. These commissural neurons, some of them propriospinal, transmit horizontal canal signals to the contralateral ventral horn, presumably to motoneurons, as well as to more caudal levels of the spinal cord.