Reorganization between preparatory and movement population responses in motor cortex.

Gamaleldin F Elsayed,Matthew T Kaufman,John P Cunningham,Antonio H Lara,Mark M Churchland

doi:10.1038/ncomms13239

Abstract

Neural populations can change the computation they perform on very short timescales. Although such flexibility is common, the underlying computational strategies at the population level remain unknown. To address this gap, we examined population responses in motor cortex during reach preparation and movement. We found that there exist exclusive and orthogonal population-level subspaces dedicated to preparatory and movement computations. This orthogonality yielded a reorganization in response correlations: the set of neurons with shared response properties changed completely between preparation and movement. Thus, the same neural population acts, at different times, as two separate circuits with very different properties. This finding is not predicted by existing motor cortical models, which predict overlapping preparation-related and movement-related subspaces. Despite orthogonality, responses in the preparatory subspace were lawfully related to subsequent responses in the movement subspace. These results reveal a population-level strategy for performing separate but linked computations.

Highlights

Neural populations can change the computation they perform on very short timescales
A canonical example occurs in the delayed-reach task, where a population of motor cortical neurons—spanning both primary and premotor cortex—participates in two processing stages
We have previously argued that one purpose of the preparatory computation is to produce a neural state that determines how neural activity evolves during the movement computation[3,11,12]

Summary

Introduction

Neural populations can change the computation they perform on very short timescales. such flexibility is common, the underlying computational strategies at the population level remain unknown. Single neurons typically exhibit different tuning (for example, a different relationship between firing rate and reach direction) during the preparatory and movement epochs[5,9,12,26,31] Despite this seemingly complex reorganization of responses, multiple lines of evidence argue that preparation and movement are mechanistically linked[3,6,32,33,34,35,36,37]. The models of Churchland et al.[11] and Sussillo et al.[42] employ this same strategy: responses during the preparatory and movement computations share some neural dimensions, but preparatory activity avoids causing premature movement by avoiding a few key dimensions that directly influence muscle activity This series of studies assumes overlapping computations

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Conclusion