Introduction Motor control requires continuous comparison between desired and actual states, yet how error signals are computed at the cellular level is not well understood. Optimal Feedback Control theory presents what computations the brain might perform during movement but not how neurons implement them [1,2]. Inhibition in sensorimotor cortex is typically framed as maintaining excitatory-inhibitory balance, shaping activity patterns, or providing gain control [3], not as computing error signals. We propose a minimal excitatory-inhibitory (E-I) circuit motif in which inhibition implements subtraction, providing a mechanistic account of error computation.
Methods
Results Individual E-I pairs produce rectified subtraction and track sinusoidal inputs up to 5 Hz with a gain above 0.5 before attenuating at higher frequencies, comfortably exceeding the approximately 2.4 Hz bandwidth imposed by muscle-tendon dynamics [4]. At the population level, linear decoders achieve R-squared greater than 0.85 for position error and velocity during centre-out reaching tasks.
Discussion
References [1] Scott, S. H. (2004). Optimal feedback control and the neural basis of volitional motor control. Nat Rev Neurosci, 5(7), 532-546. [2] Todorov, E. & Jordan, M. I. (2002). Optimal feedback control as a theory of motor coordination. Nat Neurosci, 5(11), 1226-1235. [3] Isaacson, J. S. & Scanziani, M. (2011). How inhibition shapes cortical activity. Neuron, 72(2), 231-243. [4] Crevecoeur, F. & Scott, S. H. (2014). Beyond Muscles Stiffness: Importance of State-Estimation to Account for Very Fast Motor Corrections. PLoS Comput Biol, 10(10), e1003869.
Acknowledgement This work was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to G. Blohm.
