Changes in theta and beta oscillations as signatures of novel word consolidation.

The complementary learning systems account of word learning states that novel words, like other types of memories, undergo an offline consolidation process during which they are gradually integrated into the neocortical memory network. A fundamental change in the neural representation of a novel word should therefore occur in the hours after learning. The present EEG study tested this hypothesis by investigating whether novel words learned before a 24-hr consolidation period elicited more word-like oscillatory responses than novel words learned immediately before testing. In line with previous studies indicating that theta synchronization reflects lexical access, unfamiliar novel words elicited lower power in the theta band (4-8 Hz) than existing words. Recently learned words still showed a marginally lower theta increase than existing words, but theta responses to novel words that had been acquired 24 hr earlier were indistinguishable from responses to existing words. Consistent with evidence that beta desynchronization (16-21 Hz) is related to lexical-semantic processing, we found that both unfamiliar and recently learned novel words elicited less beta desynchronization than existing words. In contrast, no difference was found between novel words learned 24 hr earlier and existing words. These data therefore suggest that an offline consolidation period enables novel words to acquire lexically integrated, word-like neural representations.