Gross anatomy of the locust brain, visual pathways, and relevant types of central complex neurons.

A. Bilateral pathways of light-sensitive neurons from the optic lobes converge onto a network in the central complex (frontal view). Stages of early visual processing include the lamina (LA), medulla (ME) and lobula (LO) of the optic lobe. Neuropils shaded red (green) are involved in an anterior (posterior) pathway of interneurons sensitive to sky compass signals. Additional pathways (yellow neuropils) might signal optic flow and / or represent features of the visual object-background scenery. DRLA (DRME), dorsal rim area of the lamina (medulla); ALO, anterior lobe of the lobula; AME, accessory medulla; AOTU, anterior optic tubercle; POTU, posterior optic tubercle; MBU (LBU) medial (lateral) bulb; LAL, lateral accessory lobe; together with the LAL, the MBU and LBU make up the lateral complex (LX). CBL (CBU) lower (upper) division of the central body; PB, protocerebral bridge; SMP, superior medial protocerebrum; CA, calyx of mushroom body. B. Relevant cell types of the central complex (frontal view). Tangential neurons invade all slices of the CBL (TL neurons) or some slices in the PB (TB1 neurons), as well as regions in a lateral complex (TL) or layers in a POTU (TB). Columnar neurons connect distinct slices of the PB to the CBU (CPU neurons) or CBL (CL neurons) of the central body and have additional arborizations in the lateral complexes. Scale bar, 100 μm.