Progressive plastic changes in the hand representation of the primary motor cortex parallel incomplete recovery from a unilateral section of the corticospinal tract at cervical level in monkeys

Abstract

After a sub-total hemi-section of the cervical cord at level C7/C8 in monkeys, a paralysis of the homolateral hand is rapidly followed by an incomplete recovery of manual dexterity, reaching a plateau after about 40-50 days, whose extent appears related to the size of the lesion. During a few days after the lesion, the hand representation in the contralateral motor cortex disappeared, replaced by representations of either face or more proximal body parts. Later, however, following a time course (about 40 days) consistent with the functional recovery, progressive plastic changes in the contralateral motor cortex took place, as demonstrated by a progressive re-appearance of digit movements elicited by intracortical microstimulation. These progressive plastic changes, which parallel the functional recovery, correspond to a re-installation of a hand representation, though substantially diminished in size as compared to pre-lesion. Regarding the functional recovery, the motor cortex (including the re-established hand area) contralateral to the unilateral cervical cord lesion played a crucial role in re-establishing control on finger movements, as assessed by reversible inactivation experiments. In contrast, the motor cortex ipsilateral to the cervical cord lesion, with largely intact projections to the spinal cord, did not contribute significantly to the recovered movements by the affected hand. These observations indicate that the CS fibers spared by the lesion are not sufficient, at least in their pre-lesion condition, to control the motoneurones innervating the digit muscles and that the pathways conveying signals from the contralateral M1 underwent reorganization.Theme G: Motor system and sensorimotor integration Topic: Cortex

Fate of rubrospinal neurons after unilateral section of the cervical spinal cord in adult macaque monkeys: Effects of an antibody treatment neutralizing Nogo-A

“…The manual dexterity performances were assessed for several months post-lesion, until the animals reached a plateau reflecting a stable level of manual dexterity. The behavioural, electrophysiological and neuroanatomical tracing data related to the CS tract derived from these animals were described in previous reports (Freund et al, , 2007Schmidlin et al, 2005Schmidlin et al, , 2004Wannier et al, 2005). The present report is focussed on anatomical aspects dealing specifically with the issue of fate of RS neurons after unilateral cervical section.…”

“…All animals included in the present study belong to a long-term research project on spinal cord lesion from which post-lesion changes in the CS system were described earlier (Freund et al, , 2007Schmidlin et al, 2005Schmidlin et al, , 2004Wannier et al, 2005). To assess the number of RS neurons in this model, midbrain sections including the red nucleus were obtained from 15 adult (3-8 years old) macaque monkeys (Macaca mulatta or Macaca fascicularis).…”

“…The surgical procedures for the unilateral spinal cord lesion at C7/C8 level have been described in detail in previous reports; (Freund et al, , 2007Schmidlin et al, 2004;Wannier et al, 2005). Briefly, the animal was anesthetized by intramuscular (i.m.)…”

“…The drawings were then aligned to allow reconstruction of the location and extent of the lesion on a transverse view of the spinal cord (Fig. 1), as previously described (Schmidlin et al, 2004;Wannier et al, 2005). In one monkey (Mk-AT, Table 1) the size of the lesion could not be estimated due to poor quality of the spinal cord tissue after histological processing.…”

Mapping the cortical representation of the lumbar paravertebral muscles

“…Changes include shrinkage of the cortical representation synonymous with the area of injury (Toldi et al 1996), the corresponding area in the uninjured cortex and invasion of adjacent territory by neighbouring representations (Nudo et al 1997). This motor cortical reorganisation can be influenced by training tasks and studies have shown that functional recovery mirrors further cortical reorganisation (Nudo et al 1996, Liepert et al 2000, Schmidlin et al 2004). …”