PT  - JOURNAL ARTICLE
AU  - Abigail A. Russo
AU  - Ramin Khajeh
AU  - Sean R. Bittner
AU  - Sean M. Perkins
AU  - John P. Cunningham
AU  - Laurence F. Abbott
AU  - Mark M. Churchland
TI  - Neural trajectories in the supplementary motor area and primary motor cortex exhibit distinct geometries, compatible with different classes of computation
AID  - 10.1101/650002
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 650002
4099  - http://biorxiv.org/content/early/2019/05/24/650002.short
4100  - http://biorxiv.org/content/early/2019/05/24/650002.full
AB  - The supplementary motor area (SMA) is believed to contribute to higher-order aspects of motor control. To examine this contribution, we employed a novel cycling task and leveraged an emerging strategy: testing whether population trajectories possess properties necessary for a hypothesized class of computations. We found that, at the single-neuron level, SMA exhibited multiple response features absent in M1. We hypothesized that these diverse features might contribute, at the population level, to avoidance of ‘population trajectory divergence’ – ensuring that two trajectories never followed the same path before separating. Trajectory divergence was indeed avoided in SMA but not in M1. Network simulations confirmed that low trajectory divergence is necessary when guidance of future action depends upon internally tracking contextual factors. Furthermore, the empirical trajectory geometry – helical in SMA versus elliptical in M1 – was naturally reproduced by networks that did, versus did not, internally track context.