Response to constant angular accelerations of neurons in the monkey superior vestibular nucleus.

The response to constant angular acceleration of type I neurons in the superior vestibular nucleus was studied in pentobarbital-anesthetized, cerebellectomized squirrel monkeys. Some so-called intact animals had six active semicircular canals. In other animals, the three canals on one side were rendered non-responsive by plugging, and data were obtained from the plugged and unplugged sides. There is no significant difference between the mean resting activities of units from the plugged and unplugged sides and from intact animals. Two observations appear to reflect a synergy of inputs from parallel canals. First, units on the unplugged side have roughly linear excitatory input-output relationships. Some plugged-side units exhibit an excitatory saturation. The nonlinear excitatory input-output relation of units from intact animals may result from addition of ipsilateral linear and contralateral nonlinear inputs. Second, the mean sensitivity to angular acceleration of units on the plugged and unplugged sides is significantly smaller than that of units from intact animals. Units responsive to stimulation in either of two canal planes showed response summation with simultaneous activation of the two inputs. Type III and type IV responses can result from such summation.