Abstracts

Rationale: A recent study found neurostimulation inadequate for cortical language mapping in children under age 10 years (Epilepsia 2007; 48:539-545). The goal of our study was to determine if recording of gamma-oscillations evoked by auditory communication localized the language areas in presurgical evaluation of children with focal epilepsy.Methods: Four children with intractable left-hemispheric focal epilepsy (3 girls ages 7, 9, & 10 years; 1 boy age 15 years) who underwent a two-stage epilepsy surgery were studied. All patients underwent preoperative MRI, extraoperative electrocorticography (ECoG), and language mapping using neurostimulation as well as gamma-oscillations. Patients received a series of 60 question-and-answer tasks. Questions were designed to elicit 1 or 2 word answers; i.e. Q: ‘What flies in the sky?’ This audible session was recorded concurrently with ECoG recording and integrated into the Digital ECoG Recording System. ECoG traces were transformed into a time-frequency matrix, which enabled sequential measurement of gamma oscillations in relation to the onset of vocalization of the patient’s answers. Alteration of gamma oscillations (50–150 Hz) compared to that during the reference period, between the completion of the patient’s vocalization and the onset of the next question, was delineated on the cortical surface via the known position of each intracranial electrode.Results: The youngest child, with developmental delay, failed to cooperate during the task. In the remaining 3 children, who successfully completed the entire session, alteration of gamma-oscillations was noted in the following sequence. i) Increased gamma-oscillations were noted in the posterior part of the superior temporal lobe when listening to the question. ii) In the time interval between question completion and the patient’s vocalization, increased gamma-oscillations were noted in the posterior frontal region, medial frontal region, and hippocampus. iii) Immediately preceding and during the patient’s vocalization, increased gamma-oscillations were noted in the pre- and post-central gyri. iv) The posterior part of the superior temporal lobe again exhibited increased gamma-oscillations immediately after the onset of and during the patient’s vocalization. In the posterior part of the superior temporal lobe showing increased gamma-oscillations, neurostimulation resulted in auditory symptoms or receptive aphasia. Neurostimulation induced expressive aphasia in a small portion of the inferior frontal but not the other areas. Sensory-motor symptoms of the mouth or throat resulted from neurostimulation of the pre- and post-central gyri showing increased gamma-oscillations.Conclusions: Recording of auditory-language-evoked gamma-oscillations may identify the cortex participating in language activity consisting of comprehension and word retrieval followed by vocalization. This time-efficient technique may supplement conventional language mapping using neurostimulation in children with focal epilepsy. NS47550