Abstracts

Rationale: Functional brain mapping is often performed to localize eloquent expressive language areas prior to resective brain surgery. Several functional mapping techniques are in common use, but all of them require active patient participation to utter words or sentences. This can prove challenging in certain populations (e.g., pediatric patients) or clinical circumstances (e.g., during awake craniotomy). In this study, we explore the possibility of using the electrocorticographic (ECoG) response to a passive receptive language task to localize eloquent expressive language areas.Methods: We recruited three human subjects with intractable epilepsy that underwent surgical implantation of 61-134 ECoG electrodes over frontal, parietal and/or temporal cortical areas. The subjects passively listened to four 17-36 seconds long stories without performing any overt tasks while we recorded their ECoG activity. We then determined those cortical locations whose ECoG activity in the broadband gamma (70-170 Hz) range changed with respect to a pre-stimulus baseline. To verify our results, we determined the cortical representation of expressive language using electrical cortical stimulation (ECS) mapping.Results: ECoG revealed increased gamma activity (p < 0.05 after Bonferroni correction) at distinct locations in the inferior frontal cortex, superior temporal gyrus and/or perisylvian areas in all three patients, and premotor and/or supplementary motor areas in two patients. All locations in inferior frontal cortex were on or in close proximity to locations that were identified using ECS (see Figure 1).Conclusions: In summary, our results show that a passive listening task activates both dorsal and ventral language streams. These results provide encouraging preliminary evidence that it may be possible to localize eloquent expressive language areas without active participation of the patient or the use of conventional frontal language tasks. Thus, with further validation in more subjects, the approach presented here may lead to a new method for identifying expressive language areas in situations where patients cannot participate appropriately with task instructions.