Anyone who has experienced trauma, or works with survivors of trauma, already that one of the most common neuromechanisms for dealing overwhelming fear is to dissociate the emotional impact from the narrative memory of the event(s). Maybe you have had the experience of someone telling you about a horrible thing that happened to him, and all the while he is smiling or even laughing. As a therapist, I immediately think, "affect incongruity." This is a clear indication that the person in question has dissociated the emotions from the experience.

The reason for this, as far as we know, is that part of what the thalamus does is assemble all of the sense data (sight, sound, touch, emotions, etc.) when encoding a memory into a coherent package, but it does not function correctly under conditions of extreme stress, so the memory ends of being fragmented. Often the emotional content gets separated out so that the person can describe the event with no related affect being visible. On the other hand, a sound associated with the trauma may trigger a flashback of the emotional experience.

We are finally beginning to understand the neuroscience behind how the brain processes trauma.

Our Brain Dissociates Emotional Response from Explicit Memory in Fearful Situations

Neuroscience News
November 6, 2014

Researchers at the Cognition and Brain Plasticity Group of the Bellvitge Biomedical Research Institute (IDIBELL) and the University of Barcelona have been tracking the traces of implicit and explicit memories of fear in human. The study was published in the journal Neurobiology of Learning and Memory; it describes how, in a context of fear, our brain differently encodes contextual memory of a negative event (the place, what we saw, etc) and the emotional response associated.

The study measures electrodermal activity of eighty-six individuals in a fearful context generated in the laboratory and in a neutral context in which they have to learn a list of words. One week and two weeks after the experiment they were tested to see which words they remembered.

“In both contexts —explains Pau Packard, author of the study—, forgetting curve was normal. Over time, they forgot all the words, the explicit trace. Moreover, in the fearful context the electrodermal activity —the emotional implicit response— was exactly the same, much higher than in the neutral context”.

In traumatic events, it seems that, over time, there is a portion of memory that is erased or inaccesible; we forget the details but still maintaining the emotional reaction. This image is for illustrative purposes only. Credit geralt.

In traumatic events, it seems that, over time, there is a portion of memory that is erased or inaccesible; we forget the details but still maintaining the emotional reaction. The imprint is divided into two separate paths. According to Packard, “the brain dissociates the explicit memory of a negative event from the emotional response”.

This may help to understand why in pathological situations of post-traumatic stress disorders, the uncontrolled emotional response linked to the negative event is generated without knowing what causes it.

Lluís Fuentemilla, project coordinator, emphasises that “the study helps to explain how the processing of fearful memories can lead to post-traumatic stress disorder”. Furthermore, it opens the door to the investigation of new therapeutic strategies for these disorders because “the implicit memory trace in a fearful context does not loose over time and can be detected through electrodermal measures”.

About this memory research

Contact: Press Office – University of Barcelona
Source: University of Barcelona press release
Image Source: The image is credited to geralt and is in the public domain

Original Research:

Packard, P. A., Rodríguez Fornells, A., Stein, L. M., Nicolás, B., and Fuentemilla, Ll. (2014, Dec). Tracking explicit and implicit long-lasting traces of fearful memories in humans. Neurobiology of Learning and Memory; 116: 96–104. Published online September 26 2014 doi:10.1016/j.nlm.2014.09.004

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Here is the original abstract from Neurobiology of Learning and Memory.

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

Pau Alexander Packarda, Antoni Rodríguez-Fornellsa, Lilian Milnitsky Stein, Berta Nicolás, Lluís Fuentemilla,

Highlights

 

• We track implicit and explicit memory traces for fearful episodes over time.

• SCR at test was higher for verbatim words encoded in a fearful context.

• Subjects were unable to report words’ emotional encoding context.

•Implicit memory traces of a fearful context was dissociated from the gist.

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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 implications towards the understanding of how the processing of fearful memories could lead to PTSD.