Gamma activity modulated by picture and auditory naming tasks: intracranial recording in patients with focal epilepsy

Abstract

Objective: We measured the spatial, temporal and developmental patterns of gamma activity augmented by picture- and auditory-naming tasks and determined the clinical significance of naming-related gamma-augmentation.

Methods: We studied 56 epileptic patients (age: 4-56 years) who underwent extraoperative electrocorticography. The picture-naming task consisted of naming of a visually-presented object; the auditory-naming task consisted of answering an auditorily-presented sentence question.

Results: Naming-related gamma-augmentation at 50-120 Hz involved the modality-specific sensory cortices during stimulus presentation and inferior-Rolandic regions during responses. Gamma-augmentation in the bilateral occipital and inferior/medial-temporal regions was more intense in the picture-naming than auditory-naming task, whereas that in the bilateral superior-temporal, left middle-temporal, left inferior-parietal, and left frontal regions was more intense in the auditory-naming task. Patients above 10 years old, compared to those younger, showed more extensive gamma-augmentation in the left dorsolateral-premotor region. Resection of sites showing naming-related gamma-augmentation in the left hemisphere assumed to contain essential language function was associated with increased risk of post-operative language deficits requiring speech therapy (p < 0.05).

Conclusions: Measurement of gamma-augmentation elicited by either naming task was useful to predict postoperative language deficits.

Significance: A smaller degree of frontal engagement in the picture-naming task can be explained by no requirement of syntactic processing or less working memory load. More extensive gamma-augmentation in the left dorsolateral-premotor region in older individuals may suggest more proficient processing by the mature brain.

Keywords: Epilepsy surgery; High-frequency oscillations (HFOs); Intracranial ECoG recording; Language; Outcome; Ripples; Speech.