MAGNETOENCEPHALOGRAPHIC LOCALIZATION OF A LANGUAGE PROCESSING CORTICAL AREA ADJACENT TO A CEREBRAL ARTERIOVENOUS MALFORMATION

In order to accurately estimate the risk of surgery for dominant peris ylvian arteriovenous malformations, the topographical relationship of the lesion to language cortex must be determined. A case is presented in which a magnetoencephalographic (MEG) study was used to map preoper atively and noninvasively an intracortical source of speech-receptive cortex in a 25-year-old right-handed man with a dominant left temporal lobe arteriovenous malformation. The speech-evoked magnetic field was analyzed at 36 positions over the left hemisphere in response to pres entations of the consonant-vowel syllables ''da'' and ''ga.'' A topogr aphical map of the magnetic component evoked at 110 msec after stimulu s onset, which was negative going to the vertex in concurrent electric al recordings, was congruent with a superficial cortical neuronal curr ent source. This source was displaced from that usually observed in no rmal individuals to tonal or click stimuli, being superior to the prob able location of auditory cortex, and superior and anterior to the pro bable location of Wernicke's area as conventionally described. The MEG results were in accord with the determination of position of a langua ge-processing cortical area as assessed by direct electrical stimulati on of the cortex during surgery under local anesthesia, and by superse lective Amytal (amobarbital) injection during angiography. The MEG rec ordings and exposed brain stimulation sites were coordinated by crania l measurements, skull x-ray landmarks, and angiographic anatomy. Inves tigations such as this, which compare MEG findings with those from est ablished clinical procedures, are an essential step in determining the physiological and anatomical utility of magnetoencephalography for no ninvasive clinical functional localization.