Abstract
An important structure in the neural circuitry for saccadic gaze shift control is the midbrain's superior colliculus (SC). It has been proposed that the SC intermediate layer lies within a gaze feedback loop and generates an error signal specifying gaze position-error (GPE), the distance between target and current gaze positions. We investigated previously this feedback hypothesis, in cat, by briefly stopping head motion during large gaze saccades made in the dark. Firing frequency of a cell gradually increased to a maximum that just preceded the optimal gaze saccade encoded by the cell's position in the caudal SC. In "brake" trials, we demonstrated that the activity-level just preceding a brake-induced gaze plateau continued steadily during the plateau and waned to zero only near the end of the corrective saccade. In the present experiments, we tested descending axonal projections of the SC neurons on the motor map to the brain stem, using antidromic mapping technique. Stimulus currents were usually restricted to less than 30μ A. Some neurons were antidromically activated by the dorsal part of the midbrain and the reticular formation. The neural activity-level continued during the brake-induced gaze plateau. Discharge pattern reflected gaze trajectory perturbations. The data suggest that the cat's tecto-reticular cell probably lies in a gaze feedback loop. [J Physiol Sci. 2006;56 Suppl:S189]
