Abstract
It has been hypothesized that the superior colliculus (SC) intermediate layer lies within a gaze feedback loop and generates an error signal specifying gaze position-error, the distance between target and current gaze positions. To test coordinated eye-head movements are controlled by feedback, we briefly (less than 400 ms) stopped head motion during gaze saccades made in the dark. At the same time, we recorded fixation neurons in cat SC that fired tonically during fixation and were silent during gaze shifts. Then, descending axonal projections of the neurons were tested, using antidromic mapping technique. Stimulus currents were usually restricted to less than 50μA. Some neurons were antidromically activated from the medial part of the pontine reticular formation. Neural activity of the neurons continued steadily during a brake-induced gaze plateau with activity-level just preceding the plateau. The activity peaked near the end of the corrective saccade. We did dot find that fixation neurons with and without descending projections show different firing patterns during gaze shift perturbations, respectively. The data suggest that the fixation cells which encode gaze position-error are updated in real time and the axons project to the omnipause neuron area. [J Physiol Sci. 2007;57 Suppl:S161]
