Magnetoencephalographic studies of language reorganization after cerebral insult

We review our experience with the application of magnetoencephalography (MEG) to the study of reorganization of the mechanisms supporting auditory language comprehension. In 3 studies, patient populations with cerebral insult of differing etiology, including epilepsy, surgical resection, and stroke, performed a running recognition task for spoken words while MEG data were collected using a whole-head magnetometer. Increased activation in the right hemisphere after left temporal lobectomy was associated with greater relative activation in that hemisphere preoperatively. Patients with chronic seizure disorder secondary to mesial temporal sclerosis exhibited a tendency toward an interhemispheric shift of language function, and those with epilepsy secondary to neoplasm showed a tendency toward an intrahemispheric shift. Patients with aphasia secondary to unilateral left-hemisphere stroke exhibited a more bilateral and diffuse overall profile of activation within the left hemisphere than control subjects of similar age. Taken together, results provide evidence that reorganization of cortex subserving auditory comprehension can occur well into the fifth and sixth decades and that the nature of the plastic response is dependent on variables such as premorbid language laterality, etiology, and, in specific groups, age at insult.