Abstracts

Rationale: Event-related gamma-augmentation on electrocorticography (ECoG) has been utilized to localize eloquent areas in patients with focal seizures who undergo epilepsy surgery. Functional cortical mapping using ECoG has recently received growing attention among epileptologists and cognitive neuroscientists, since it can monitor cortical signals with (i) a temporal resolution of order of tens of milliseconds, (ii) a spatial resolution of 1 cm or below, (iii) signal-to-noise ratio 20 to >100 times better than that of scalp EEG, and (iv) minimal electromyographic artifacts associated with overt articulation. Here, we studied the spatial-temporal dynamics of cortical activity during overt phoneme articulation, using animation movies of event-related ECoG signal changes.Methods: We measured gamma band (70-110 Hz) and low-frequency band (10-30 Hz) ECoG amplitudes during self-paced, overt articulation of 44 American English phonemes. We then compared the temporal-spatial patterns of ECoG amplitude modulations across phoneme classes.Results: Regardless of the place or manner of phoneme articulation, gamma augmentation initially involved a common site within the left inferior Rolandic area. Subsequently, gamma augmentation and/or attenuation involved distinct sites within the left sensorimotor area for the lip and tongue with a variable timing across phoneme places. Finally, gamma-augmentation took place, uniformly at the onset of sound generation, in a throat sensorimotor area, and effectively distinguished voiced and unvoiced phonemes. Gamma-attenuation involved the left inferior-frontal and superior-temporal regions simultaneously during articulation. Low-frequency band attenuation involved the Rolandic areas during articulation but poorly distinguished different phonemes.Conclusions: Our results support the notion that articulation of distinct phonemes recruits specific sensori-motor activation. Gamma attenuation in the left inferior frontal and superior temporal regions may reflect transient functional suppression in these structures during automatic, self-paced vocalization of phonemes containing no semantic or syntactic information. Measurement of event-related alteration of gamma band activity, compared to that of low-frequency band, may be more useful for decoding of the underlying articulatory functions.