Electrosensory pathways to the valvula cerebelli in mormyrid fish.

The valvula cerebelli of mormyrid fish has been implicated in the electroreceptive capabilities of these animals. This study uses peroxidase and tritiated amino acid tracing techniques to examine the pathways by which electroreceptive information gains access to the valvula. Ampullary and mormyromast receptor information reaches the medial and ventrolateral portions of the valvula by means of a large, direct projection from n. lateralis, part of the midbrain electrosensory area. In addition, smaller indirect n. lateralis-valvular projections travel via a pretectal nucleus and the so-called postventral thalamic nucleus, Knollenorgan receptor information ends in the dorsolateral portion of the valvula. A small, relatively direct pathway runs via n. medialis ventralis, but most Knollenorgan information appears to travel via an indirect system involving n. extrolateralis pars posterior and n. isthmi. The lateral line processing areas of the valvula project back onto many of the midbrain electrosensory nuclei. These results indicate that much of the cerebellum of this family is devoted to sensory processing rather than motor functions.