The Sensory Functions of the Cerebellum of the Thornback Ray, Platyrhinoidis triseriata

Summary

Single unit spikes and evoked field potentials were recorded in different parts and depths of the corpus cerebelli and auricle of immobilized rays before and after stimulating with light, electric fields, touch, tail bending and direct shock to mechanoreceptive nerves of the lateral line.

Discrete areas of the cerebellum are responsive to these modalities and the areas show limited overlap; they are all distinct from the area reported by Plassmann to be responsive to angular acceleration. The visual and tactile-proprioceptive areas are large; the electric area is small. Most units are excited only by one modality.

The tail is represented only in the posterior lobe; trigeminal innervation extends from the posterior onto the anterior lobe, suggesting some topographic projection.

The dynamic characteristics of the responses were examined particulary in the visual units. To a flash, units discharge up to six bursts of spikes in 500 ms. This pattern is reduced at repetition rates >1/s; above ca. 4/s units tend to fire irregularly. Various kinds of units are found in respect to the succession of responses to short trains of flashes. Some units fire much better to objects moving in a limited visual field with a certain direction and rate.