Abstracts

Rationale: Invasive studies of patients with focal epilepsy have established and expanded many generally-accepted theoretical frameworks for the functional neuroanatomy of speech and language function; the generalization of such findings is possible because the presence of focal epilepsy does not imply the entire brain to be abnormal. Here, we have provided 3D and 4D mapping of speech and language function based upon results of direct cortical stimulation and event-related modulation of electrocorticography (ECoG) signals. Methods: Patients estimated to have right-hemispheric language dominance were excluded. Thus, 100 patients with focal epilepsy who underwent two-stage epilepsy surgery with chronic ECoG recording were studied. An older group consisted of 84 patients at least 10 years of age (7367 artifact-free nonepileptic electrodes), whereas a younger group included 16 children younger than age 10 (1438 electrodes). The probability of symptoms transiently induced by electrical stimulation was delineated on a 3D average surface image. The ECoG amplitude changes of high-gamma (70-110 Hz) and beta (15-30 Hz) activities during an auditory-naming task were animated on the average surface image in a 4D manner. Thereby, high-gamma augmentation and beta-attenuation were treated as a summary measure of cortical activation. Results: Stimulation data indicated the causal relationship between (1) auditory hallucination and bilateral superior-temporal gyri, (2) receptive aphasia and left superior/middle-temporal gyri, (3) expressive dysphasia and widespread temporal/frontal lobes in the left hemisphere, and (4) speech arrest and bilateral precentral gyri. On ECoG analysis, high-gamma augmentation involved the bilateral superior-temporal and precentral gyri immediately following onset of an auditory question; at the same time, high-gamma activity was slightly but significantly attenuated in the left inferior-frontal gyrus. High-gamma activity was augmented in the left middle/inferior-frontal, middle/inferior-temporal, inferior-parietal, supplementary motor, parahippocampal, entorhinal, and cingulate areas, maximally around question offset. Also at question offset, high-gamma activity was attenuated in the right middle-frontal, and inferior parietal gyri. Immediately before verbal response, high-gamma augmentation involved the bilateral supplementary motor, precentral and postcentral areas; at the same time, high-gamma activity was attenuated in the right superior-temporal gyri. Beta-attenuation was spatially and temporally correlated with high-gamma augmentation in general. The younger and older groups shared similar spatial-temporal profiles of high-gamma and beta modulation. Yet, the younger group failed to show left-dominant activation in the middle-frontal and inferior-parietal gyri. Conclusions: The human brain may rapidly and alternately activate and deactivate cortical areas advantageous or obtrusive to function directed toward speech and language at a given moment. Increased left- dominant activation in the middle-frontal and inferior parietal gyri in the older age group may reflect developmental consolidation of the language system. The results of our functional mapping may be useful in predicting, across not only space but also time and patient age, sites specific to language function for presurgical evaluation of patients with focal epilepsy. Funding: NIH grant NS64033 (to E. Asano)