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Neurobiol Learn Mem. 2014 Dec;116:96-104. doi: 10.1016/j.nlm.2014.09.004. Epub 2014 Sep 26.

Tracking explicit and implicit long-lasting traces of fearful memories in humans.

Author information

1
Cognition and Brain Plasticity Group, Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain; Department of Basic Psychology, University of Barcelona, Barcelona, Spain. Electronic address: paupackard@gmail.com.
2
Cognition and Brain Plasticity Group, Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain; Department of Basic Psychology, University of Barcelona, Barcelona, Spain; Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain.
3
Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Brazil.
4
Cognition and Brain Plasticity Group, Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain.
5
Cognition and Brain Plasticity Group, Bellvitge Biomedical Research Institute (IDIBELL), Barcelona, Spain; Department of Basic Psychology, University of Barcelona, Barcelona, Spain.

Abstract

Recent accounts of Posttraumatic Stress Disorder (PTSD) suggest that the encoding of an episode within a fearful context generates different implicit and explicit memory representations. Whilst implicit memory traces include the associated emotional states, explicit traces include a recoding into an abstract or gist-based structural context of the episode. Theoretically, the long-term preservation of implicit memory traces may facilitate the often untreatable memory intrusions in PTSD. Here, we tracked in two experiments how implicit and explicit memory traces for fearful episodes dissociate and evolve over time. Subjects (N=86) were presented with semantically-related word-lists in a contextual fear paradigm and tested for explicit memories either immediately (i.e., 30 min) or after a delay (i.e., 1 or 2 weeks) with a verbal recognition task. Skin Conductance Response (SCR) was used to assess implicit memory responses. Subjects showed high memory accuracy for words when tested immediately after encoding. At test, SCR was higher during the presentation of verbatim but not gist-based words encoded in a fearful context, and remained unchanged after 2 weeks, despite subjects being unaware of words' encoding context. We found no clear evidence of accurate explicit memory traces for the fearful or neutral contexts of words presented during encoding, either 30 min or 2 weeks afterwards. These findings indicate that the implicit, but not the explicit, memory trace of a fearful context of an episode can be detected at long-term through SCR and is dissociated from the gist-based memory. They may have implicationstowards the understanding of how the processing of fearful memoriescould lead to PTSD.

KEYWORDS:

Contextual fear; Explicit memory; Gist-based memory; Implicit memory; Posttraumatic Stress Disorder; Psychophysiology

PMID:
25256154
DOI:
10.1016/j.nlm.2014.09.004
[Indexed for MEDLINE]

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