Episodic retrieval is reflected by a process specific increase in human electroencephalographic theta activity

Is an increase in theta during retrieval due (primarily) to the access of a stored code or to more general processes? The electroencephalogram was rec orded while subjects performed a recognition task with pictures. According to the event-related desynchronization/synchronization method, the percenta ge of band power changes was calculated during encoding and retrieval for a theta and three alpha bands. Significant results were obtained (with minor exceptions) only in the theta band. The increase in theta was significantl y larger during retrieval than during encoding but did not differ significa ntly between new and successfully retrieved old pictures. Because a memory trace is lacking for new pictures, the increase in theta during retrieval r eflects primarily general processing demands of a complex episodic memory s ystem. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.