A model for visual naming based on spatiotemporal dynamics of ECoG high-gamma modulation.

ABSTRACT

OBJECTIVE: We studied spatiotemporal dynamics of electrocorticographic (ECoG) high-gamma modulation (HGM) during visual naming. METHODS: In 8 patients, aged 4-19 years, with left hemisphere subdural electrodes, propagation of ECoG HGM during overt visual naming was mapped with trial-averaged time-frequency analysis. Group-level synthesis was performed by transforming all electrodes to a standard space and assigning cortical parcels based on a reference atlas. RESULTS: After image display following cortical parcels were activated inferior occipital, caudal angular, fusiform, and middle temporal gyri, and superior temporal sulcus [0-400 ms]; rostral pars triangularis (A45r), inferior frontal sulcus, caudal dorsolateral premotor cortex (A6cdl) [300-600 ms]; caudal ventrolateral premotor cortex (A6cvl), caudal pars triangularis (A45c), pars opercularis (A44) [400-800 ms]; primary sensorimotor cortex [600-1400 ms], with most prominent HGM in glossolaryngeal region (A4tl). Lastly, auditory cortex (A41/A42) and superior temporal gyrus (A22) were activated [900 ms-1.4 s]. After 1.5 s, HGM decreased globally, except in ventrolateral premotor cortex. CONCLUSIONS: During visual naming, ECoG HGM shows a sequential but overlapping spatiotemporal course through cortical regions. We provide neurophysiologic validation for a model of visual naming incorporating both modular and distributed cortical processing. This may explain cognitive deficits seen in some patients after surgery involving HGM naming sites outside perisylvian language cortex.