EPISODIC AND SEMANTIC MEMORY - AN ANALYSIS IN THE EEG THETA-BAND AND ALPHA-BAND

This study examines the hypothesis that in contrast to semantic memory processes that are assumed to be reflected primarily within the alpha band, episodic memory processes are related to activity within the th eta band. EEG signals were recorded from subjects as they performed a semantic congruency and an episodic recognition task. In the semantic task, subjects had to judge whether or not sequentially presented conc ept-feature pairs (such as ''eagle-claws'' or ''pea-huge'') are semant ically congruent. In the episodic task, which followed the semantic ta sk without prior warning, the same word pairs were presented together with new distracters (generated by repairing known concept-feature pai rs). Here, subjects judged whether or not a particular concept-feature pair was already presented during the semantic task. EEG data were an alyzed using event-related desynchronization (ERD) as a measure for th e amount of event-related changes in band power in the theta band and in the upper and lower alpha bands. The alpha band was determined indi vidually, using the alpha peak frequency during the resting period as the cut-off point to separate the lower from the upper alpha band. The results, which are based on those identical word pairs that demanded a yes response in both tasks, showed that semantic memory processes ar e indeed primarily reflected in the upper alpha band whereas episodic memory processes are reflected in the theta band. The possible relatio nship between hippocampal theta activity and the encoding of episodic information is discussed.