Abstracts

Rationale: Identification and preservation of the sites critical for picture naming and reading are clinically important in presurgical evaluation of epileptic patients. Removal of such sites may lead to functional deficits and decreased quality of life in patients with focal epilepsy. We measured the presence or absence of gamma-augmentations in response to two types of visual tasks consisting of picture naming and word reading. Gamma augmentation can be a measure of cortical activation elicited by a task. Methods: We studied four patients (ages ranging from 9 to 17) with focal epilepsy (three on the left hemisphere and one on the right) who underwent extraoperative electrocorticography (ECoG) recording followed by cortical resection. Patients implanted with extensive subdural grids on the side of the presumed epileptic focus were asked overtly name images presented sequentially in the picture naming task and asked to read and vocalize written words in the reading task. ECoG signals recorded during these tasks were transformed to time-frequency matrices, and the amplitudes of gamma-oscillations at 50-150 Hz were compared to those during the resting reference period. Cortical sites showing statistically-significant gamma-augmentation were identified. Results: Gamma-augmentation commonly elicited by both tasks was found in the caudal occipital area, bilaterally. Gamma-augmentation commonly elicited by vocalization was found in the Rolandic area, bilaterally. Picture naming tasks preferentially induced more gamma-augmentation in portions of occipital, temporal, and pre-motor areas in comparison to word reading tasks, bilaterally (i.e. these areas were less active during word reading tasks). Likewise, word reading tasks preferentially and selectively induced gamma-augmentation in portions of left parietal area as well as right occipital-temporal area. Conclusions: Gamma-augmentation measured on ECoG can identify cortical areas commonly and differentially involved in picture naming and reading tasks in patients with focal epilepsy.