The Structural Basis of Information Processing in the Visual System of the Bee

Abstract

The optic lobes of the bees are composed of three ganglia. From the periphery inward, the three regions are known as the lamina, the medulla and the lobula. The three optical ganglia are connected to each other by the outer chiasma which connects the lamina with the medulla and the inner chiasma which connects the medulla with the lobula (Fig. 1). The first optic ganglion, the lamina, is a neuropil zone consisting of thousands of cylindrical units, the optical cartridges, which receive the inputs of the receptor cell axons (RCA’s). The nine RCA’s emerging from the ommatidium, project in one bundle either as short visual fibers (svf) or long visual fibers (lvf) to the cartridge below. In addition to the RCA’s and the four different L-neurons in each cartridge an unknown number of tangential, centrifugal, and horizontal fiber elememts are found. The medulla, like the retina and lamina, shows in its distal layers a highly regular arrangement of axon bundles. The visual information reaches the medulla through at least seven channels either directly from the retina via the three long visual fibers or after relay from the six short visual fibers via the four L-fiber types. The main neuronal elements in the medulla are the transmedullary cells and an unknown number of tangential and amacrine cells. Y- and T- cells link the medulla with the third optic ganglion. The lobula is a multi-stratified, spherical-shaped ganglion. The three outermost strata contain endings of the transmedullary cells and those of the shallow endings of Y- and T-cells. The neuronal endings leave the ganglion in several fibre bundles and project to the posterior or anterior protocerebrum.