Theta oscillations and the ERP old/new effect: independent phenomena?

Objectives: The hypothesis is examined whether a memory-related change in induced band power (oscillatory old/new effect) is functionally related to a memory-related increase in ERP positivity (ERP old/new effect). Methods: In order to avoid a confounding on the measurement level, induced band power (IBP) was used as a measure that is devoid of the influence of evoked components. The EEG was recorded during a recognition memory task. Results: The results show that compared to correctly rejected words, targets (remembered words) elicit a significantly larger P300. An oscillatory old/new effect was found for the delta and theta but not for the alpha band. It is manifested by an increase in delta and theta IBP which is significantly larger for targets than for correctly rejected words. It can be observed during the same time interval and shows the same topographic distribution as the ERP old/new effect. Most importantly, however, the ERP old/new effect (as well as the P300 itself) is generated by very slow frequencies which Lie below the delta band. Conclusions: These findings demonstrate that the two types of old/new effects are functionally related. Possible physiological mechanisms underlying this relationship are discussed in terms of a threshold change in the cortex (generating the P300) that occurs during an increase in hippocampal theta activity (generating an increase in induced theta power). (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.