The effects of memory load on event-related EEG desynchronization and synchronization

Objectives: To examine the effects of working memory load on the event-rela ted desynchronization (ERD) and synchronization (ERS) of several narrow EEG frequency bands. Methods: ERD/ERS responses of the 4-6, 6-8, 8-10 and 10-12 Hz EEG frequency bands were studied in 24 normal subjects performing a visual sequential le tter task (so-called n-back task) in which memory load was varied from 0 to 2. Results: In the 3-6 Hz theta frequency band, a long-lasting synchronization was observed in the anterior electrodes, especially after the presentation of targets. In the 6-8 and 8-10 Hz frequency bands, anterior ERS was elici ted especially in the 2-back condition (highest memory load). In contrast t o the responses of the 8-10 Hz frequency band, in the 10-12 Hz frequency ba nd the 2-back experimental condition elicited the greatest ERD. Conclusions: In the highest memory load (2-back) experimental condition the attentional capacities were most probably exceeded, resulting in 6-8 and 8 -10 Hz ERS. This might reflect an inhibition of such brain areas (frontal c ortices) no longer involved in task completion when alternative strategies are needed and utilized. These more 'cognitive' strategies were then reflec ted as an increase in 10-12 Hz ERD. Additionally, our results support the a ssumption that the simultaneously recorded ERD/ERS responses of different n arrow EEG frequency bands differ and reflect distinct aspects of informatio n processing. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.