'Paradoxical' alpha synchronization in a memory task

The results of a specially designed memory search paradigm which maximizes episodic short-term memory (STM) and minimizes semantic long-term memory (L TM) demands show that the upper alpha band synchronizes selectively in thos e conditions and time intervals where episodic STM demands are maximal. Thi s finding of a selective alpha synchronization occurring only in the upper alpha band and during highest task demands is surprising because it is well known that usually alpha desynchronizes during mental activity. Because ex periments from our laboratory indicate that desynchronization in the upper alpha band is related to semantic LTM processes, the present finding sugges ts that a selective synchronization in this frequency band reflects inhibit ion of semantic LTM. It is assumed that once the capacity limits of STM are reached or exceeded, processing resources are no longer distributed and th at potentially interfering, task irrelevant, brain areas or processing syst ems are inhibited. (C) 1999 Elsevier Science B.V. All rights reserved.