Somatosensory representation in patients who have undergone hemispherectomy: a functional magnetic resonance imaging study

Object. Removal or disconnection of an entire cerebral hemisphere is occasionally used to treat refractory seizures. Patients who have undergone a hemispherectomy provide useful models to study the reorganization of cortical somatosensory representation. This plasticity may be a consequence of the pathological lesion: the hemispherectomy itself, or both. Methods. Three patients who had undergone hemispherectomy were studied with functional magnetic resonance (fMR) imaging. Responses to sensory stimulation in normal hands and hands opposite the lesioned hemisphere were studied. Multislice T-2*-weighted gradient-echo echoplanar images were obtained using a 1.5-tesla MR imager. The activation condition consisted of somatosensory stimulation of the index finger. A T-1-weighted anatomical MR image was acquired. The fMR and anatomical MR images were coregistered, and statistically significant activation foci (p < 0.01) were identified. Stimulation of the normal hand produced activation in the primary somatosensory cortex (SI) in all patients. Stimulation of the impaired hand resulted in activation of the ipsilateral parietal operculum (second somatosensory area [SII]) and posterior parietal lobe (Brodmann's Area 7) in all cases, but no activation was elicited in the SI in any patient. In addition, other areas within the ipsilateral frontal and parietal lobes were activated in some individuals. Conclusions. Residual somatosensory function in the hand opposite the lesioned hemisphere is mediated by the SII and other cortical regions in the intact hemisphere, without involvement of the SI.