The Physiology and Morphology of Centrally Projecting Visual Interneurones in the Honeybee Brain

Visual interneurones with projections into the median protocerebrum of the honeybee brain were characterized by electrophysiological and neuroanatomical methods. Extrinsic medulla neurones with wide ramifications in the medulla and terminations in the median posterior protocerebrum show spatial opponency in their tonic responses to stationary light. Wide-field lobula neurones projecting into the dorsal lobe code the direction of movement of visual stimuli by changing the sign of their tonic response. Lobula neurones, with two branches ipsiand contralateral to the oesophagus, are binocularly sensitive. A moving stimulus in either direction causes excitation or inhibition of these neurones, the sign of the response being dependent on the side of stimulation. The presumed dendrites of an extrinsic lobula neurone, showing combined spectral and spatial opponency, differ markedly in shape from those of lobula movement-detecting neurones. Neurones that connect the optic tubercle with the contralateral dorsal lobe are characterized. They show a non-directionally selective movement sensitivity within a binocular receptive field.