Chapter 24 A Brain Region in Insects That Supervises Walking

Abstract

Publisher Summary Central pattern generator circuits provide rhythmic patterns of activity among connected neurons that mediate walking. Local perturbations, such as irregularities in ground height, are relayed to central pattern generators by feedback from many thousands of mechanoreceptors. This sensory information is integrated locally by spiking and nonspiking local interneurons that control and maintain patterned firing among motoneurons. Local circuits integrate information about leg position, allowing compensatory adjustments at the leg joints for maintaining posture and gait. In many insect species, local sensory afferents and the thoracic nervous system could alone maintain forward locomotion. Circuits underlying locomotion toward a stimulus source appear to be more complexly organized than those mediating escape behaviors. Descending neurons that relay information from the brain to thoracic ganglia have several discrete dendritic domains in the brain, which usually receive sensory inputs indirectly through ensembles of interneurons. In addition, many descending neurons that supply leg motor circuits also receive connections from a prominent midline neuropil, called “the central complex.” This chapter discusses some of the known properties of this center and speculates about the significance of its structure. To date, behavioral genetics, electrophysiology, and comparative anatomy all suggest that the central complex plays a cerebellar-like role in controlling forward locomotion, change of direction, and other limb actions. However, before considering the central complex, it is important to outline the segmental organization of the insect brain and to emphasize the unique position of the central complex within the three pre-oral ganglia.