Abstracts

Rationale: Measurement of the amplitude of high-gamma oscillations (70-110Hz) on electrocorticography (ECoG) is a useful method to determine the temporal dynamics of cortical processing during sensorimotor and cognitive tasks. Language processing in response to verbal stimuli is characterized by sequential augmentation of high-gamma oscillations in neocortex. The present study characterized the temporal and spatial profiles of high-gamma activations in pre-surgical cases of drug-resistant focal epilepsy. Independent component analysis (ICA) was employed to determine unbiased principle activations in the superior temporal gyrus (STG). Below, we report the activation patterns with coherent spatial clustering in relationship to language processing. Methods: A total of 93 patients were studied after excluding those with massive brain malformations, severe cognitive dysfunction, previous epilepsy surgery, non-English primary language, or right-hemisphere language dominance. Platinum macroelectrodes (10 mm inter-contact) were placed subdurally as part of presurgical evaluation of patients with focal epilepsy at Detroit Medical Center. All subdural electrodes were registered on a standard 3D brain surface image. Chronic ECoG data was obtained with a sampling rate at 1000 Hz. While awake and comfortably seared on a bed, patients completed an auditory naming task as described in Figure 1 below. Subsequent ECoG signals underwent fast ICA in MATLAB. Results: ICA of the STG revealed several major patterns of activation alongside their spatial distribution. Eight primary components are presented in Figure 2 below. Conclusions: The results of this study have raised a hypothesis that functional compartments may exist in a mosaic manner within the STG. Presence of early/brief high-gamma activation (Figure 2B) and sustained activation throughout stimulus presentation (Figure 2A) may indicate that ‘detection of sound onset’ and ‘continuous perceptual processing’ are exerted by two distinctive systems within the STG. Late and persistent activation maximized at stimulus offset (Figure 2E) may be related to high-order cognitive processing to comprehend given auditory questions. Funding: NIH Grant NS64033 (E. Asano)