The reorganization of sensorimotor function in children after hemispherectomy. A functional MRI and somatosensory evoked potential study.

Children who have suffered extensive unilateral brain injury early in life may show a remarkable degree of residual sensorimotor function. It is generally believed that this reflects the high capacity of the immature brain for cerebral reorganization. In this study, we investigated 17 patients who had undergone hemispherectomy for relief from seizures; eight of the patients had congenital brain damage and nine had sustained their initial insult at the age of 1 year or older. Sensorimotor functions of the hand were investigated using functional MRI (fMRI) during a passive movement task, somatosensory evoked potentials (SEPs) arising from electrical and vibration stimulation, and behavioural tests including grip strength, double simultaneous stimulation and joint position sense. On fMRI, two of the eight patients studied with this technique (one with congenital damage and one with damage acquired at the age of 3 years) showed activation in the sensorimotor cortex of the remaining hemisphere with passive movement of the hemiplegic hand. The location of the ipsilateral brain activation was similar to that found on movement of the normal contralateral hand, although the latter was greater in spatial extent. In one of these patients, a greater role was demonstrated for the ipsilateral secondary sensorimotor area (compared with the ipsilateral primary sensorimotor area) for movement of the hemiplegic hand than for movement of the normal hand. Median nerve stimulation of the hemiplegic hand showed reproducible early-latency ipsilateral SEP components in the remaining sensorimotor cortex in 10 of the 17 patients (five with congenital and five with acquired disease). Five of the patients who demonstrated ipsilateral electrical SEPs also showed ipsilateral vibration SEPs (two with congenital and three with acquired disease). The behavioural tests revealed residual sensorimotor function in 14 of the patients; however, not all of the patients who exhibited ipsilateral SEP or fMRI responses had residual sensorimotor function in the hemiplegic hand. Ipsilateral sensorimotor responses were demonstrated both in patients with congenital disease and those with acquired disease, suggesting that factors additional to aetiology and age at injury may influence the degree of residual sensorimotor function and cerebral reorganization.