Extensive Cortical Convergence to Primate Reticulospinal Pathways

Karen M Fisher, Boubker Zaaimi, Steve A Edgley, Stuart N Baker

Research output: Contribution to journalArticlepeer-review


Early evolution of the motor cortex included development of connections to brainstem reticulospinal neurons; these projections persist in primates. In this study, we examined the organization of corticoreticular connections in five macaque monkeys (one male) using both intracellular and extracellular recordings from reticular formation neurons, including identified reticulospinal cells. Synaptic responses to stimulation of different parts of primary motor cortex (M1) and supplementary motor area (SMA) bilaterally were assessed. Widespread short latency excitation, compatible with monosynaptic transmission over fast-conducting pathways, was observed, as well as longer latency responses likely reflecting a mixture of slower monosynaptic and oligosynaptic pathways. There was a high degree of convergence: 56% of reticulospinal cells with input from M1 received projections from M1 in both hemispheres; for SMA, the equivalent figure was even higher (70%). Of reticulospinal neurons with input from the cortex, 78% received projections from both M1 and SMA (regardless of hemisphere); 83% of reticulospinal cells with input from M1 received projections from more than one of the tested M1 sites. This convergence at the single cell level allows reticulospinal neurons to integrate information from across the motor areas of the cortex, taking account of the bilateral motor context. Reticulospinal connections are known to strengthen following damage to the corticospinal tract, such as after stroke, partially contributing to functional recovery. Extensive corticoreticular convergence provides redundancy of control, which may allow the cortex to continue to exploit this descending pathway even after damage to one area. 2021 Fisher et al.

Original languageEnglish
Pages (from-to)1005-1018
Number of pages14
JournalJournal of Neuroscience
Issue number5
Early online date2 Dec 2020
Publication statusPublished - 3 Feb 2021

Bibliographical note

Copyright © 2020 Fisher et al.
This is an open-access article distributed under the terms of the Creative Commons Attribution
4.0 International license, which permits unrestricted use, distribution and reproduction in any
medium provided that the original work is properly attributed.


  • Intracellular
  • Primate
  • Reticular formation
  • Neurons/physiology
  • Male
  • Macaca mulatta
  • Reticular Formation/physiology
  • Spinal Cord/physiology
  • Membrane Potentials/physiology
  • Pyramidal Tracts/physiology
  • Motor Cortex/physiology
  • Animals
  • Excitatory Postsynaptic Potentials/physiology
  • Neural Pathways/physiology
  • Female


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