Abstract

Cue integration and flexible action selection are essential elements of brain function. A key open question is how these operations are implemented at the level of circuit connectivity and cellular physiology. My laboratory has recently been investigating this question by focusing on the upper motor neurons of the Drosophila brain – i.e., the neurons that project to the ventral nerve cord (the “spinal cord”). We have been recording from these cells in walking flies while also presenting sensory guidance cues. We have identified several types of upper motor neurons whose dendritic arbors reside mainly in the lateral accessory lobe (LAL), a brain region involved in limb control. We have found that the LAL integrates guidance cues from higher sensory regions, including visual, olfactory, and mechanosensory regions. It is also bidirectionally connected to the brain region which contains the representation of the organism’s heading direction. We find that LAL upper motor neurons encode both multisensory variables and motor variables related to orienting (turning) behaviors. The LAL is involved in selecting among competing sensory cues, representing latent biases in action selection, and gating turns based on salience cues. These findings provide a foundation for a more mechanistic understanding of how spatial guidance cues, contextual salience cues, and internal brain states are integrated to produce flexible motor control.