Spatio-temporal dynamics of working memory maintenance and scanning of verbal information

•Intracranial electrocorticography recording revealed high-gamma augmentation during working memory maintenance in the left precentral gyrus.•Such precentral high-gamma augmentation was larger when memory load was increased.•Left inferior-frontal and supra-marginal gyri showed high-gamma augmentation during scanning.

ObjectiveDuring verbal communication, humans briefly maintain mental representations of speech sounds conveying verbal information, and constantly scan these representations for comparison to incoming information. We determined the spatio-temporal dynamics of such short-term maintenance and subsequent scanning of verbal information, by intracranially measuring high-gamma activity at 70-110 Hz during a working memory task.MethodsPatients listened to a stimulus set of two or four spoken letters and were instructed to remember those letters over a two-second interval, following which they were asked to determine if a subsequent target letter had been presented earlier in that trial's stimulus set.ResultsAuditory presentation of letter stimuli sequentially elicited high-gamma augmentation bilaterally in the superior-temporal and pre-central gyri. During the two-second maintenance period, high-gamma activity was augmented in the left pre-central gyrus, and this effect was larger during the maintenance of stimulus sets consisting of four compared to two letters. During the scanning period following target presentation, high-gamma augmentation involved the left inferior-frontal and supra-marginal gyri.ConclusionsShort-term maintenance of verbal information is, at least in part, supported by the left pre-central gyrus, whereas scanning by the left inferior-frontal and supra-marginal gyri.SignificanceThe cortical structures involved in short-term maintenance and scanning of speech stimuli were segregated with an excellent temporal resolution.