Abstract
The “subsequent memory paradigm” is an analysis tool to identify brain activity elicited during episodic encoding that is associated with successful subsequent retrieval. Two commonly observed event-related potential “subsequent memory effects” (SMEs) are the parietal SME in the P300 time window and the frontal slow wave SME, but to date a clear characterization of the circumstances under which each SME is observed is missing. To test the hypothesis that the parietal SME occurs when aspects of an experience are unitized into a single item representation, while inter-item associative encoding is reflected in the frontal slow wave effect, participants were assigned to one of two conditions that emphasized one of the encoding types under otherwise matched study phases of a recognition memory experiment. Word pairs were presented either in the context of a definition that allowed to combine the word pairs into a new concept (unitization or item encoding) or together with a sentence frame (inter-item encoding). Performance on the recognition test did not differ between the groups. The parietal SME was only found in the definition group, supporting the idea that this SME occurs when the components of an association are integrated in a unitized item representation. An early prefrontal negativity also exhibited an SME only in this group, suggesting that the formation of novel units occurs through interactions of multiple brain areas. The frontal slow wave SME was pronounced in both groups and may thus reflect processes generally involved in encoding of associations. Our results provide evidence for a partial dissociation of the eliciting conditions of the two types of SMEs and therefore provide a tool for future studies to characterize the different types of episodic encoding.
Highlights
A widely used approach to study the neuro-cognitive basis of episodic encoding is to compare physiological activity elicited by to-be-encoded stimuli between those that are retrieved on a subsequent memory test, vs. those that are not
Under otherwise matched encoding conditions and in the absence of behavioral differences in recognition performance, event-related potentials (ERPs) subsequent memory effects” (SMEs) elicited by word pairs encoded in the context of an entity defining framework, promoting the formation of a single item representation, differed from those elicited by word pairs encoded in an interitem associative encoding task
Our results demonstrate that in the absence of behavioral differences in memory performance, the ERP components that vary in amplitude with subsequent retrieval success depend on the nature of the encoding task
Summary
A widely used approach to study the neuro-cognitive basis of episodic encoding is to compare physiological activity elicited by to-be-encoded stimuli between those that are retrieved on a subsequent memory test, vs. those that are not. While this “subsequent memory paradigm” (for reviews, see Wagner et al, 1999; Paller and Wagner, 2002; Werkle-Bergner et al, 2006) was first applied to event-related potentials (ERPs; Sanquist et al, 1980; Karis et al, 1984), recently the majority of studies have used functional magnetic resonance imaging (fMRI). The present study was designed to resolve some of these inconsistencies by characterizing the circumstances under which two SMEs with specific spatio-temporal characteristics occur.
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