The Physiology and Morphology of Visual Commissures in the Honeybee Brain

ABSTRACT Visual commissures of the honeybee brain were investigated by electrophysiological and histological methods. A newly described serpentine optic commissure (SOC) consists of four neurones each of which has widely extending arborizations in both medullae and lobulae. The cells are monocularly sensitive, the best stimulus being a moving target. Neurones of the posterior optic commissure (POC) connect the two medullae and show spatial opponency; the sign of the tonic response depends on the position of the stimulus in the receptive field of the cell. The inferior optic commissure (IOC) assembles neurones that have ramifications in both lobulae. They show directional selectivity to a moving stimulus and this is often combined with an opponent tonic response. The anterior optic commissure (AOC) contains neurones which are similar to those of the IOC and which connect the two lobulae. These show a preferential sensitivity to one direction of movement. A single pair of cells close to the interoptic tubercle commissure is identified as being movement-sensitive without directional selectivity.