EEG correlates of subvocal rehearsal, familiarity and recollection, and behavior.

摘要

EEG signals have recently been implicated in working memory, particularly during encoding, retention, and retrieval. Different processes govern the retention of information in nonverbal and verbal working memory, the latter depending specifically on Subvocal rehearsal of items. During retrieval, dual-process theorists posit that two components of the event-related potential (ERP), the N400 and the P300, index the processes of familiarity and recollection, respectively. We explored EEG signals in search of correlates of Subvocal rehearsal, familiarity and recollection, and behavior.; We recorded scalp EEG's on subjects performing a Sternberg memory task using verbal stimuli (letters, words, and pictures of common objects) and nonverbal stimuli (spatial dot locations and sinusoidal grating patterns). We found oscillatory correlates unique to verbal stimuli in the 4--8 Hz theta, 9--12 Hz alpha, 14--28 Hz beta, and 30--50 Hz gamma frequency bands. Verbal stimuli elicited greater power than nonverbal stimuli bilaterally in theta, in frontal and occipital areas in alpha and beta, and centrally in gamma. Looking specifically for instances where power in the tune intervals between item presentations was greater than power during presentations, we found enhanced beta oscillations in the frontal and occipital regions. During retrieval, we found that the N400 differentiated old from new verbal stimuli, but did not differentiate old from new nonverbal stimuli. However, the P300 differentiated old from new for both verbal and nonverbal stimuli types. We conclude that beta oscillations are involved in verbal Subvocal rehearsal, and that familiarity requires a semantic label, whereas recollection does not.; When we searched for correlates of behavior, we found that enhanced theta oscillations in the left parietal, central, and right parietal regions were correlated with recognition, difficulty, and memory load, respectively. Oscillations at other frequencies were also correlated with behavior, with the amplitude of 2--4 Hz delta increasing with memory strength and the amplitude of 25--60 Hz gamma increasing with longer reaction times. Our observations indicate that the functional roles of oscillations vary throughout the brain.