Long-term motor cortical map changes following unilateral lesion of the hand representation in the motor cortex in macaque monkeys showing functional recovery of hand functions

Purpose: How are motor maps modified within and in the immediate vicinity of a damaged zone in the motor cortex of non-human primates? Methods: In eight adult macaque monkeys subjected to a restricted chemical lesion of the hand area in the primary motor cortex (M1), motor maps were established using intracortical micro-stimulation (ICMS) techniques. The monkeys were subdivided into five animals without treatment, whereas three monkeys received an anti-Nogo-A antibody treatment. Results: Following permanent M1 injury, the lesion territory became largely non micro-excitable several months post-lesion, in spite of some recovery of hand function. Few sites within the lesion territory remained excitable, though irrespective to the degree of functional recovery. Around the lesion in M1, there was no reallocation of proximal shoulder/arm territories into distal hand functions. However, ICMS delivered at supra-threshold intensities in these proximal territories elicited digit movements. Post-lesion ICMS thresholds to elicit movements of forelimb muscle territories increased, independently from the degree of functional recovery. Further behavioural evidence for an enhancement of functional recovery promoted by the anti-Nogo-A antibody treatment is provided. Conclusion: The degree of functional recovery is not related to a reorganization of motor maps within, and in the vicinity of, a M1 lesion.