The subesophageal ganglion modulates locust inter-leg sensory-motor interactions via contralateral pathways

Electrophysiological experiments and anatomical staining suggest that sensory signals from leg nerves are transmitted to the SEG through the connective contralateral to the stimulation site, processed and pass to the other side of the ventral nerve chain as descending commands to the local motor centers. [Display omitted] •The locust SEG modulates interactions between thoracic sensory inputs and motor output.•The SEG is essential for intersegmental transfer of leg’ sensory-related signals.•Similar to vertebrates, ascending pathways are mainly contralateral. The neural control of insect locomotion is distributed among various body segments. Local pattern-generating circuits at the thoracic ganglia interact with incoming sensory signals and central descending commands from the head ganglia. The evidence from different insect preparations suggests that the subesophageal ganglion (SEG) may play an important role in locomotion-related tasks. In a previous study, we demonstrated that the locust SEG modulates the coupling pattern between segmental leg CPGs in the absence of sensory feedback. Here, we investigated its role in processing and transmitting sensory information to the leg motor centers and mapped the major related neural pathways. Specifically, the intra- and inter-segmental transfer of leg-feedback were studied by simultaneously monitoring motor responses and descending signals from the SEG. Our findings reveal a crucial role of the SEG in the transfer of intersegmental, but not intrasegmental, signals. Additional lesion experiments, in which the intersegmental connectives were cut at different locations, together with double nerve staining, indicated that sensory signals are mainly transferred to the SEG via the connective contralateral to the stimulated leg. We therefore suggest that, similar to data reported for vertebrates, insect leg sensory-motor loops comprise contralateral ascending pathways to the head and ipsilateral descending ones.