Visual fields of butterfly interneurons

Abstract

A relatively novel and precise technique was employed for the detailed plotting of the extent and nature of the fields of fibres in the visual pathway of 11 species of butterflies. For these experiments, a moving, flashing spot of light on the face of an oscilloscope was used as a photostimulator. Some 160 fibres were analysed by this technique. In many cases, the response to light adaptation was observed. Unlike many previous reports, units were found to have exceedingly complex fields, not easily described. Two major categories of optic lobe units were detected. These included: (1) fibres with large diffuse fields with many ‘holes’ and channels within their substance, which were markedly altered by light adaptation, and (2) relatively uncommon, smaller visual fields, which were somewhat more uniform in responsiveness. Four categories of visual fields were recorded in the protocerebrum. These included: (1) units with a large, diffuse field with a sharp boundary corresponding to the horizon, (2) binocular fields with much, little, or no overlap, (3) large diffuse fields, not unlike those discovered in the optic lobe, and (4) fibres demonstrating an inhibitory influence and resulting decrease in the size of the visual field as a result of contralateral stimulation.