Skilled reaching relies on a V2a propriospinal internal copy circuit.
The precision of skilled forelimb movement has long been presumed to rely on rapid feedback corrections triggered by internally directed copies of outgoing motor commands, but the functional relevance of inferred internal copy circuits has remained unclear. One class of spinal interneurons implicated in the control of mammalian forelimb movement, cervical propriospinal neurons (PNs), has the potential to convey an internal copy of premotor signals through dual innervation of forelimb-innervating motor neurons and precerebellar neurons of the lateral reticular nucleus. Here we examine whether the PN internal copy pathway functions in the control of goal-directed reaching. In mice, PNs include a genetically accessible subpopulation of cervical V2a interneurons, and their targeted ablation perturbs reaching while leaving intact other elements of forelimb movement. Moreover, optogenetic activation of the PN internal copy branch recruits a rapid cerebellar feedback loop that modulates forelimb motor neuron activity and severely disrupts reaching kinematics. Our findings implicate V2a PNs as the focus of an internal copy pathway assigned to the rapid updating of motor output during reaching behaviour.
Howard Hughes Medical Institute, Kavli Institute for Brain Science, Mortimer B. Zuckerman Mind Brain Behavior Institute, Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, New York 10032, USA.
Eiman
E
Azim
Department of Integrative Medical Biology, Section of Physiology, Umeå University, Umeå, Sweden.
Juan
J
Jiang
Department of Integrative Medical Biology, Section of Physiology, Umeå University, Umeå, Sweden.
Bror
B
Alstermark
Howard Hughes Medical Institute, Kavli Institute for Brain Science, Mortimer B. Zuckerman Mind Brain Behavior Institute, Departments of Neuroscience and Biochemistry and Molecular Biophysics, Columbia University, New York, New York 10032, USA.
Thomas M
TM
Jessell
D000818:Animals; D002531:Cerebellum / Q000502:physiology; D025461:Feedback, Physiological; D005260:Female; D005552:Forelimb / Q000294:innervation* / Q000502:physiology*; D007395:Interneurons / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology*; D009048:Motor Skills / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D009434:Neural Pathways; D062308:Optogenetics; D011597:Psychomotor Performance / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology*