(Re-)organization of the developing human brain following periventricular white matter lesions.

Unilateral periventricular brain lesions served as a model for the investigation of (re-)organization following insults to the developing human brain. In both the motor and the language systems (re-)organization was observed in the contra-lesional hemisphere. In the motor system, the contra-lesional hemisphere can develop (or maintain) ipsilateral cortico-spinal projections to the paretic hand; in the language system, left-sided lesions can induce (re-)organization of speech production in the right hemisphere. This interhemispheric (re-)organization can achieve normal language functions, whereas the hand contra-lateral to the lesion always remains markedly impaired. Despite these functional differences, the two systems share common principles concerning their reorganizational mechanisms: (1) Interhemispheric (re-)organization always occurred in areas homotopic to the "original" areas in the affected hemisphere, (2) the degree of interhemispheric (re-)organization correlated with structural damage to hand or facial motor tracts, and (3) afferent functions (the somatosensory hand representation, the perception of speech) did not follow their efferent counterparts (the motor hand representation, and the production of speech), but remained in the affected hemisphere.