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Identification of a cellular node for motor control pathways
Ariel J Levine13, Christopher A Hinckley13, Kathryn L Hilde1,2, Shawn P Driscoll1,2, Tiffany H Poon1,2, Jessica M Montgomery1,2 & Samuel L Pfaff1,2
The rich behavioral repertoire of animals is encoded in the CNS as a set of motorneuron activation patterns, also called motor synergies. However, the neurons that orchestrate these motor programs as well as their cellular properties and connectivity are poorly understood. Here we identify a population of molecularly defined motor synergy encoder (MSE) neurons in the mouse spinal cord that may represent a central node in neural pathways for voluntary and reflexive movement. This population receives direct inputs from the motor cortex and sensory pathways and, in turn, has monosynaptic outputs to spinal motorneurons. Optical stimulation of MSE neurons drove reliable patterns of activity in multiple motor groups, and we found that the evoked motor patterns varied on the basis of the rostrocaudal location of the stimulated MSE. We speculate that these neurons comprise a cellular network for encoding coordinated motor output programs.
npg 201 4 Nature America, Inc. All rights reserved.
Common movements, such as reaching and grasping an object or stepping, involve complex neural calculations to select the appropriate muscles and precisely control the timing of their contractions to achieve the desired outcome. This motor coordination involves many regions in the central nervous system (CNS), including the motor cortex, red nucleus, basal ganglia, brainstem, cerebellum, peripheral sensory system and spinal neurons. These neural pathways ultimately converge onto motorneuron pools that are each dedicated to controlling a single muscle of the body. Given the number of muscles and possible joint positions of the body that can vary at each moment, the efficiency and reliability of common movements are remarkable.
To simplify the motor-control tasks of the CNS, neural plans for compound movements that invoke multiple joints or body regions are thought to be fractionated into a series of subroutines or synergies that bind together useful combinations of motorneuron activation13.
These synergies may then be flexibly recruited into multiple types of movement, such as voluntary and reflexive behaviors. It has long been recognized that voluntary movements and those evoked by direct stimulation of the motor cortex...