Hierarchy in influence but not firing patterns among forelimb motor cortices

Abstract

AbstractThough hierarchy is commonly invoked in descriptions of neural system function, its presence and manifestation in firing patterns remain poorly resolved. Here we use rapid activity perturbations to demonstrate asymmetric influence between premotor and primary motor cortices on fast timescales during reaching in mice, confirming hierarchy among endogenous firing patterns. However, this hierarchy had a surprising manifestation: firing in each region was dominated by temporally-aligned patterns and was equally predictive of future firing in the other region. Network modeling suggests an explanation: functional hierarchy can be determined by the relative dependence of local circuits on across-region input, rather than asymmetry in that input. We propose that motor cortical firing patterns are primarily defined not by across-region input, but by the constraints of patterning motor output.