Electrophysiological study of the posterior accessory optic tract

Abstract

Electrophysiological methods were used to detect the presence of the posterior accessory optic tract—transpeduncular tract in the rabbit. Photic stimulation gave rise to mainly an ‘on’ response from the contralateral nucleus of the transpeduncular tract. Electrical stimulation of the optic nerve fibers evoked a response from this nucleus with a latency of 1–3 msec. A response could not be elicited from the nucleus of the transpeduncular tract, the lateral geniculate nucleus, or the superior colliculus by ipsilateral stimulation. Encéphale isolé preparations showed that the responses recorded under urethane anesthesia were not altered by the drug. The nucleus of the posterior accessory optic tract is situated between the optic nerve and the nucleus of the transpeduncular tract, and lies on the dorsolateral aspect of the midbrain between the superior colliculus and the medial geniculate nucleus. No centrifugal fiber responses have been found which originate from the nucleus of the transpeduncular tract and pass to the retina via the optic nerve.