Plasticity in the developing brain: neurophysiological basis for lesion-induced motor reorganization

Abstract

The plasticity of the developing brain can be observed following injury to the motor cortex and/or corticospinal tracts, the most commonly injured brain area in the pre- or peri-natal period. Factors such as timing of injury, lesion size, and lesion location may affect a single hemisphere’s ability to acquire bilateral motor representation. Bilateral motor representation of single hemisphere origin is most likely to occur if brain injury occurs before the age of 2 years; however, the link between injury etiology, reorganization type, and functional outcome is largely understudied. We performed a retrospective review to examine reorganized cortical motor maps identified through transcranial magnetic stimulation in a cohort of 52 patients. Subsequent clinical, anthropometric, and demographic information was recorded for each patient. Each patient’s primary hand motor cortex center of gravity, along with the Euclidian distance between reorganized and normally located motor cortices, was also calculated. The patients were classified into broad groups including reorganization type (inter- and intra-hemispheric motor reorganization), age at time of injury (before 2 years and after 2 years), and injury etiology (developmental disorders and acquired injuries). All measures were analyzed to find commonalities between motor reorganization type and injury etiology, function, and center of gravity distance. There was a significant effect of injury etiology on type of motor reorganization (P < 0.01), with 60.7% of patients with acquired injuries and 15.8% of patients with developmental disorders demonstrating interhemispheric motor reorganization. Within the inter-hemispheric motor reorganization group, ipsilaterally and contralaterally projecting hand motor cortex centers of gravity overlapped, indicating shared cortical motor representation. Furthermore, the data suggest significantly higher prevalence of bilateral motor representation from a single hemisphere in cases of acquired injuries compared to those of developmental origin. Functional outcome was found to be negatively affected by acquired injuries and inter-hemispheric motor reorganization relative to their respective developmental lesions and counterparts with intra-hemispheric motor reorganization. These results provide novel information regarding motor reorganization in the developing brain via an unprecedented cohort sample size and transcranial magnetic stimulation. Transcranial magnetic stimulation is uniquely suited for use in understanding the principles of motor reorganization, thereby aiding in the development of more efficacious therapeutic techniques to improve functional recovery following motor cortex injury.

The role of early functional neuroimaging in predicting neurodevelopmental outcomes in neonatal encephalopathy

“…If replicated in larger-scale studies, these results may improve the ability to predict CP in newborns with NE before clinical evidence and promote early targeted educational interventions. We hypothesized that the negative responses observed in the right sensorimotor area of the newborns who later develop CP might be related to oxygen consumption associated with possible synaptogenesis due to brain plasticity and motor reorganization [8,32]. These mechanisms might also explain why this relationship was only observed in the right hemisphere, in addition to the eventual maturational asymmetry, cortical hemisphere preference, or influence of the stimulus type.…”