Bilateral visual inputs to the dorsal cap of inferior olive: differential localization and inhibitory interactions.

There are two pathways known to mediate optic signals to the rabbit flocculus through the dorsal cap of the inferior olive; one (I) projects from the contralateral and the other (II) from the ipsilateral eye, both to the contralateral flocculus. The present study on anesthetized rabbits revealed that the two pathways are relayed at different loci of the dorsal cap, I at its caudal and II its rostral half. The ventrolateral outgrowth of the inferior olive also projects to the flocculus, but a prominent field potential could not be produced by optic signals. The present study further demonstrated that transmission in pathway I accompanies an inhibitory action upon that in II. Since direct stimulation of these pathways at preolivary levels revealed similar inhibition, and since this was reflected in the depression of antidromic invasion of dorsal cap neurons, it is concluded that inhibition occurs postsynaptically in dorsal cap neurons. Inhibition is unidirectional, as activities in pathway II did not influence those in I.