Visual system of calliphorid flies: motion- and orientation-sensitive visual interneurons supplying dorsal optic glomeruli.

Intracellular recordings accompanied by dye fills were made from neurons associated with optic glomeruli in the lateral protocerebrum of the brain of the blowfly Phaenicia sericata. The present account describes the morphology of these cells and their electrophysiological responses to oriented bar motion. The most dorsal glomeruli are each supplied by retinotopic efferent neurons that have restricted dendritic fields in the lobula and lobula plate of the optic lobes. Each of these lobula complex cells represents a morphologically identified type of neuron arranged as an ensemble that subtends the entire monocular visual field. Of the four recorded and filled efferent types, three were broadly tuned to the orientation of bar stimuli. At the level of optic glomeruli a relay neuron extending centrally from optic foci and a local interneuron that arborizes among glomeruli showed narrow tuning to oriented bar motion. The present results are discussed with respect to the behavioral significance of oriented motion discrimination by flies and other insects, and with respect to neuroanatomical data demonstrating the organization of deep visual neuropils.