THE BRAIN OF THE HONEYBEE APIS-MELLIFERA .1. THE CONNECTIONS AND SPATIAL-ORGANIZATION OF THE MUSHROOM BODIES

The mushroom bodies of the bee are paired neuropils in the dorsal part of the brain. Each is composed of the arborizations of over 17 .times. 104 small interneurons of similar architecture called Kenyon cells. Golgi staining demonstrates that these neurons can be divided into 5 groups. The mushroom body neuropils each consist of a pair of cup-shaped structures, the calyces, connected by 2 short fused stalks, the pedunculus, to 2 lobes, and .alpha.- and .beta.-lobes. Each calyx is formed from 3 concentric neuropil zones, the basal ring, the collar and the lip. The calyces are organized in a polar fashion; within the calyces each of the 5 categories of Kenyon cell has a distribution limited to particular polar contours. The dendritic volumes of neighboring Kenyon cells arborizing within each individual contour are greatly overlapped. Fibers from groups of neighboring cells within a calycal contour are gathered into bundles that project into the pedunculus, each fiber dividing to enter both the .alpha.- and .beta.-lobes. The pedunculus and the lobes are layered. Kenyon cells with neighboring dendritic fields within the same calycal contour occupy a single layer in the pedunculus and lobes. The 2-polar organization of the calyces is transformed into a Cartesian map within the pedunculus, which continues into the .alpha.- and .beta.-lobes. The calyx receives input fibers from both the antennal lobes and the optic neuropils. The branching patterns of these cells reflect the polar organization of the calyces as their branches are restricted to 1 or more of the 3 gross compartments of the calycal neuropil. Cells considered to represent outputs from the mushroom bodies arborize in the pedunculus and .alpha.- and .beta.-lobes. Arborizations of the output neurons reflect the layered organization of these neuropils. Fibers from the 2 lobes run to the anterior median and lateral protocerebral neuropil, and the anterior optic tubercle. There is an extensive network of feedback interneurons that interconnect the .alpha.- and .beta.-lobes with the ipsi- and contralateral calyces. Many individual neurons have branches in both the .alpha.- and the .beta.-lobes and in the pedunculus. The pathways and geometries of the fibers subserving the 2 lobes are described. The anatomy of the bee''s mushroom bodies suggests that they process 2nd-order antennal and 4th- and higher-order visual information.