INT - Institut de Neurosciences de la Timone

The capacity to elaborate coordinated movements is essential for most, if not all, behaviors. The executive circuits for movements, i.e. that directly trigger muscular contractions, reside in the spinal cord but are under obligatory control of supra-spinal inputs. Important descending command pathways for movement take origin in the reticular formation (RF) of the brainstem. However, the organizational logic that allows the coordinated control of multiple component actions during multi-faceted motor behaviors is unclear. How do different executive circuits interact functionally ? Are they under common descending control ? Is there some form of somatotopic organization, or functional specialization, of descending motor pathways by action type ? We address here these questions taking the example of locomotor movements and their coordination with orienting movements and breathing. Our work favors a multifunctional role of specific motor centers in the brainstem. It also underscores the existence of functional, behavior-specific, modules defined by genetic identities but argues for a muscle group oriented functional specialization at the connectomics level within modules. The latter may underlie the control of the individual actions of coherent and multi-faceted motor behaviors.