Neural oscillations involved in self-referential processing

Human adults remember better trait words that are referenced to the self than those referenced to others. To investigate whether non-phase-locked neural oscillations engage in the self-reference effect, we recorded electroencephalogram (EEG) from healthy adults during trait judgments of the self and a familiar other. The wavelet analysis was used to calculate non-phase-locked time-frequency power associated with encoding of trait adjectives referenced to the self or the familiar other at theta (5-7 Hz), alpha (8-13 Hz), beta (14-27 Hz) and gamma (28-40 Hz) bands. We found that, relative to other-referential traits, self-referential traits induced event-related synchronization of theta-band activity over the frontal area at 700-800 ms and of alpha-band activity over the central area at 400-600 ms. In contrast, event-related desynchronization associated with self-referential traits was observed in beta-band activity over the central-parietal area at 700-800 ms and in gamma-band activity over the fronto-central area at 500-600 ms. Moreover, valence of traits referenced to the self and self-relevance of traits respectively led to modulations of theta/alpha- and beta/gamma-band activity. Finally, event-related synchronization of frontal theta-band activity at 700-800 ms positively correlated with the self-reference effect observed during memory retrieval. Our results indicate that non-phase-locked neural activity is involved in self-reflexive thinking. In addition, low and high-frequency neural oscillations play different roles in emotional and cognitive aspects of self-reference processing.