Central coordination of electromotor and locomotor pathways in the weakly electric fish Brevimyrus niger.

Coordinating multiple motor outputs is essential for active sensing. Mormyrid weakly electric fish generate electric organ discharges (EODs) while swimming, providing a tractable system for studying central mechanisms of motor coordination. The optic tectum (OT), homolog of the mammalian superior colliculus (SC), is a conserved sensorimotor center that regulates orienting behaviors and is reciprocally connected with the central electromotor network in mormyrid fish. Further, stimulation of the OT can elicit fictive swimming. However, whether the OT coordinates locomotor and electromotor outputs remains unknown. By combining electrical recordings with precise behavioral tracking in freely swimming Brevimyrus niger , we found that changes in EOD rate reliably preceded swimming movements, suggesting a temporal hierarchy of motor control. In paralyzed in vivo preparations, local OT microstimulation elicited both fictive EODs and fictive swimming, with the same temporal ordering observed during behavior. Spatial analyses revealed that fictive swimming was elicited more by stimulation of deeper OT regions. Similarly, fictive EODs were elicited more by stimulation of deeper and more ventroposterior regions, consistent with previous anatomical findings. Furthermore, OT stimulation sites that elicited higher rates of fictive EODs also tended to elicit more fictive swimming, suggesting that the OT provides a common drive to electromotor and locomotor systems. Together, our results extend the conserved role of the OT/SC in coordinating orienting behaviors to the active electrosensory system of weakly electric fish.