Title:  Population Interactions in the Motor System

While several brain regions involved in controlling movement have been identified, the neural signal processing that ultimately governs motor commands sent to muscles has remained stubbornly opaque. Synaptic interactions within and between neuronal populations are probable loci of this processing, but historically it has been extremely challenging in practice to observe these interactions at cellular and spike resolution during behavior. Mechanistic models of motor system operation in real time during movement execution are thus lacking. Work in my lab aims to characterize interactions within and between motor system populations as a means to build and refine such models. During my talk, I will first discuss a line of research that addresses how motor cortical output engages downstream effector circuits. Historical views of motor system organization all share a common feature: they impute distinct functions onto distinct subsets of cells. In motor cortex, subpopulations of neurons are thought to drive particular muscle groups or movement types, implying that signals are conveyed to downstream targets by activity in specific neuronal subpopulations. However, our recent work suggests that motor cortical activity is not dominated by a muscle- or task-based organization, but that changes in the activity covariation of motor cortical output induce downstream circuits to respond in a task-specific manner. Thus the taxonomy of motor system function may need an additional layer that reflects task-specific population dynamics. I will also discuss another line of research addressing the common view of a functional hierarchy among motor cortices in which a premotor cortex primarily plans voluntary movements, while a downstream primary motor cortex is involved chiefly with the execution of voluntary movements. Here we are using multielectrode array recording and optogenetics together with emerging methods for quantifying neuronal interactions on fast synaptic timescales to assess functional hierarchy among motor cortices.

Dr. Miri is an Assistant Professor in the Department of Neurobiology at Northwestern University.

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