Changes in descending motor pathway connectivity after corticospinal tract lesion in macaque monkey

Boubker Zaaimi, Steve A. Edgley, Demetris S. Soteropoulos, Stuart N. Baker*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Damage to the corticospinal tract is a leading cause of motor disability, for example in stroke or spinal cord injury. Some function usually recovers, but whether plasticity of undamaged ipsilaterally descending corticospinal axons and/or brainstem pathways such as the reticulospinal tract contributes to recovery is unknown. Here, we examined the connectivity in these pathways to motor neurons after recovery from corticospinal lesions. Extensive unilateral lesions of the medullary corticospinal fibres in the pyramidal tract were made in three adult macaque monkeys. After an initial contralateral flaccid paralysis, motor function rapidly recovered, after which all animals were capable of climbing and supporting their weight by gripping the cage bars with the contralesional hand. In one animal where experimental testing was carried out, there was (as expected) no recovery of fine independent finger movements. Around 6 months post-lesion, intracellular recordings were made from 167 motor neurons innervating hand and forearm muscles. Synaptic responses evoked by stimulating the unlesioned ipsilateral pyramidal tract and the medial longitudinal fasciculus were recorded and compared with control responses in 207 motor neurons from six unlesioned animals. Input from the ipsilateral pyramidal tract was rare and weak in both lesioned and control animals, suggesting a limited role for this pathway in functional recovery. In contrast, mono- and disynaptic excitatory post-synaptic potentials elicited from the medial longitudinal fasciculus significantly increased in average size after recovery, but only in motor neurons innervating forearm flexor and intrinsic hand muscles, not in forearm extensor motor neurons. We conclude that reticulospinal systems sub-serve some of the functional recovery after corticospinal lesions. The imbalanced strengthening of connections to flexor, but not extensor, motor neurons mirrors the extensor weakness and flexor spasm which in neurological experience is a common limitation to recovery in stroke survivors.

Original languageEnglish
Pages (from-to)2277-2289
Number of pages13
Issue number7
Publication statusPublished - 1 Jul 2012

Bibliographical note

© The Author (2012). Published by Oxford University Press on behalf of the Guarantors of Brain.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


  • Plasticity
  • Post-stroke recovery
  • Primate
  • Pyramidal tract lesion
  • Reticulospinal tract


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