Imaging recovery from stroke.

Brain imaging techniques illustrate the plastic potential even of the adult human brain in healthy subjects as in patients with peripheral or central lesions. Recovery of lost function through a persistent structural lesion in the central nervous system is accompanied by a complex and individually variable pattern of reorganisation of the brain. Changes depend on the site of the lesion and are found in both hemispheres, the damaged and the sound one within a pre-existing, widespread and bilateral organised and parallel processing network without the formation of new centres. This implies changes at rest with increased or decreased activity and altered activation patterns during performance of the restituted function. Within the primary motor system an activation at the rim of the infarct, extension into neighbouring representations, which outflow is not disturbed, altered recruitment pattern of motor cortex neurons, and recruitment of ipsilateral direct descending corticospinal tract pathways originating in the sound hemisphere are found. Disruption of the primary system leads to re-weighting of activity between the various representational levels with increased activity in secondary of higher order areas. Early sensory reorganisation indicates the potential for recovery of lost motor function. Behavioural language training in aphasics results in improvement of altered comprehension function, which is related to right hemisphere activation. Thus, reorganisation can be beneficial and training or rehabilitation influence the pattern of reorganisation.