The structural basis of developmental plasticity in the human brain

Our objective was to review the spatial and temporal factors which determine structural plasticity of the developing fiber pathways in the human fetal and preterm brain. The fiber pathways show structural plasticity (detouring, rerouting, sprouting) during initial outgrowth, pathway selection phase, „waiting“, target- and address selection phase (temporal parameters) occuring in sequential developmental „windows“. The „plastic“ changes take place in the following compartments: internal capsule, periventricular cross-roads, intermediate zone, subplate and cortical plate (spatial parameters). The most prominent compartment in the human cerebrum is subplate which contains afferent fibers during „waiting“ period.

Using histological techniques on postmortem brains of preterms and children who died after various post-lesion survival and histological-magnetic resonance correlation on „normal“ brains we have obtained results which shed new light on pathways plasticity.

Thalamocortical fibers may be rerouted if periventricular lesion occurs before 24–26 weeks post conception (wpc), during a „waiting“ period in the subplate. Long cortico-cortical pathways cause formation of new convolutions around porencephalic cavity, after damage of their prospective cortical target area. The developmental peak of this plasticity is around 34 wpc, during the existence of subplate zone. Corpus callosum is the most affected fibre system due to the fact that it grows through numerous periventricular cross-roads, rich in axonal guidance molecules. In analysis of efferent pathways we have found enhanced compartmentalization of the putamen after bilateral caudate lesion. This phenomenon may be explained by rerouting of ipsilateral and contralateral corticocaudate projection to putamen.

The presented spatial and temporal parameters of structural plasticity of growing pathways can be studied using neuroimaging methods and applied for planing the treatment in children with prenatal brain injury.