Elsevier

Neuropsychologia

Volume 46, Issue 13, November 2008, Pages 3021-3029
Neuropsychologia

Reviews and perspectives
Brain substrates of implicit and explicit memory: The importance of concurrently acquired neural signals of both memory types

https://doi.org/10.1016/j.neuropsychologia.2008.07.010Get rights and content

Abstract

A comprehensive understanding of human memory requires cognitive and neural descriptions of memory processes along with a conception of how memory processing drives behavioral responses and subjective experiences. One serious challenge to this endeavor is that an individual memory process is typically operative within a mix of other contemporaneous memory processes. This challenge is particularly disquieting in the context of implicit memory, which, unlike explicit memory, transpires without the subject necessarily being aware of memory retrieval. Neural correlates of implicit memory and neural correlates of explicit memory are often investigated in different experiments using very different memory tests and procedures. This strategy poses difficulties for elucidating the interactions between the two types of memory process that may result in explicit remembering, and for determining the extent to which certain neural processing events uniquely contribute to only one type of memory. We review recent studies that have succeeded in separately assessing neural correlates of both implicit memory and explicit memory within the same paradigm using event-related brain potentials (ERPs) and functional magnetic resonance imaging (fMRI), with an emphasis on studies from our laboratory. The strategies we describe provide a methodological framework for achieving valid assessments of memory processing, and the findings support an emerging conceptualization of the distinct neurocognitive events responsible for implicit and explicit memory.

Section snippets

Explicit memory and perceptual implicit memory

Identifying neural correlates of perceptual implicit memory processes uncontaminated by those of explicit memory processes is problematic because of the difficulty of preventing subjects from recalling prior episodes or recognizing repeated stimuli during priming tests. Similarly, automatic perceptual implicit memory processing may occur during explicit memory tests, even if no indications of perceptual implicit memory are observed in behavior, and this processing can potentially be reflected

Explicit memory and conceptual implicit memory

Conceptual implicit memory can occur when concepts are repeated, and behavioral measures of conceptual implicit memory are similar to those of perceptual implicit memory in that they can occur in the absence of awareness of remembering and typically take the form of faster or more accurate responses to a specific stimulus in a conceptual priming test. These alterations of behavioral responses are thought to reflect facilitated processing of relevant meaning, and potentially support some of the

Acknowledgements

The research support was provided by grant 0518800 from the National Science Foundation and grants R01-NS34639 and P30-AG13854 from the National Institutes of Health. J.L.V. was supported by National Institutes of Health grant T32-AG20506. Small portions of this article appear in Voss and Paller (2008).

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