Abstracts

Rationale: The frontal eye field (FEF) extends posteriorly to the anterior/lateral surface of the pre-central gyrus, part of Brodmann area 6, the premotor region. Direct electrical stimulation of the pre-central part of FEF often leads to contralateral eye deviation. Electrocorticographic findings have yielded data suggesting rapid visual as well as auditory processing located within this region in addition to ocular motor function. In order to investigate the functional role of pre-central FEF in auditory language, we determined the spatial-temporal characteristics of high-gamma oscillations in the 50-150 Hz range during auditory naming and auditory working memory tasks. We also employed contrast tasks to ‘dissect' language from non-language functions by adding non-human auditory stimuli on the auditory naming task. Methods: We studied a total of 10 patients with focal epilepsy who underwent chronic electrocorticographic recording. Patients were instructed to vocalize a semantically-correct answer (e.g.: Answer "Bird" for an auditory question "What flies in the sky?") during the auditory naming task, and to determine the presence of a repeated letter of the Alphabet (e.g.: Answer "Yes" for auditory stimuli: "L", "X", "B", "N", ‘two seconds of silence', "X") during the working memory task; 2 and 4 letter strings were provided in order to vary the working memory requirement. Patients were instructed to state "I don't know" when non-human auditory stimuli were provided. Results: Within this same small region associated with lateral eye deviation induced by electrical stimulation, we found rapid human-voice-specific high-gamma augmentation, similar to that of the superior temporal gyrus. We also found high-gamma augmentation in the same region during the period of working memory maintenance (i.e. : within the two seconds of silence). Findings related to working memory maintenance demonstrated a dose-reponse phenomenon, which greater augmentation with 4-letter stimuli compared to 2-letter stimuli. Conclusions: We believe that this compact region, consisting of precentral FEF, may play a unique role in cognition and may even explain certain everyday behaviors. Functions related to eye movement, language-related audition, and working memory maintenance functions have been demonstrated. Further studies with finer electrode grids with spatial resolution smaller than our 1cm may reveal a more complex functional architecture rather than a single region carrying out multiple simultaneous functions.