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 o r central lesions. Recovery of lost function through a persistent stru ctural lesion in the central nervous system is accompanied by a comple x and individually variable pattern of reorganisation of the brain. Ch anges depend on the site of the lesion and are found in both hemispher es, the damaged and the sound one within a pre-existing, widespread an d bilateral organised and parallel processing network without the form ation of new centres. This implies changes at rest with increased or d ecreased activity and altered activation patterns during performance o f the restituted function. Within the primary motor system an activati on at the rim of the infarct, extension into neighbouring representati ons, which outflow is not disturbed, altered recruitment pattern of mo tor cortex neurons, and recruitment of ipsilateral direct descending c orticospinal tract pathways originating in the sound hemisphere are fo und. Disruption of the primary system leads to re-weighting of activit y between the various representational levels with increased activity in secondary of higher order areas. Early sensory reorganisation indic ates the potential for recovery of lost motor function. Behavioural la nguage training in aphasics results in improvement of altered comprehe nsion function, which is related to right hemisphere activation. Thus, reorganisation can be beneficial and training or rehabilitation influ ence the pattern of reorganisation.