Surprise! Changing Emotional Memories – “Amygdala Dopamine Receptors Are Required for the Destabilization of a Reconsolidating Appetitive Memory” – Research Review

In this study, the authors find that dopamine is linked with the destabilization of emotional memories, making them more able to change. Possible applications to disorders such as PTSD and addiction.

Paper — Merlo, et al. 2015. Amygdala Dopamine Receptors Are Required for the Destabilization of a Reconsolidating Appetitive Memory.

Abstract

Disrupting maladaptive memories may provide a novel form of treatment for neuropsychiatric disorders, but little is known about the neurochemical mechanisms underlying the induction of lability, or destabilization, of a retrieved consolidated memory. Destabilization has been theoretically linked to the violation of expectations during memory retrieval, which, in turn, has been suggested to correlate with prediction error (PE). It is well-established that PE correlates with dopaminergic signaling in limbic forebrain structures that are critical for emotional learning. The basolateral amygdala is a key neural substrate for the reconsolidation of pavlovian reward-related memories, but the involvement of dopaminergic mechanisms in inducing lability of amygdaladependent memories has not been investigated. Therefore, we tested the hypothesis that dopaminergic signaling within the basolateral amygdala is required for the destabilization of appetitive pavlovian memories by investigating the effects dopaminergic and protein synthesis manipulations on appetitive memory reconsolidation in rats. Intra-amygdala administration of either the D1-selective dopamine receptor antagonist SCH23390 or the D2-selective dopamine receptor antagonist raclopride prevented memory destabilization at retrieval, thereby protecting the memory from the effects of an amnestic agent, the protein synthesis inhibitor anisomycin. These data show that dopaminergic transmission within the basolateral amygdala is required for memory labilization during appetitive memory reconsolidation.

The study was performed on “77 experimentally naïve male Lister-Hooded rats (Charles River) housed in pairs in a vivarium on a reversed light-dark cycle (lights on at 1900 hours).” They chose this sample size based upon predictions from other studies.

“Significance Statement”

Memories are not fixed in the brain, but undergo experience-dependent updating and modification through reconsolidation. This occurs when a memory is converted to a labile state, usually involving surprise (formally, prediction error), which is in turn linked to release of dopamine. We hypothesized that neurotransmission via dopamine receptors in the amygdala, a region critical for emotional memory processing, is required for memory destabilization. The results show that blocking dopamine receptors in the amygdala protected reward-associated memories from an amnestic treatment. Therefore, dopamine is required for the induction of pavlovian memory lability, supporting a link between destabilization and prediction error. Thus, dopaminergic signaling allows memories to be dynamic and flexible, providing a novel target for the modification of maladaptive memories.

In other words:

Experience causes memories to update and modify — usually because of surprise (and similar experiences that cause you to make a “prediction error”). This event is linked with a release in dopamine.

Surprise can cause memories to destabilize, making them more likely to change.

Your Amygdala is a region of your brain important for the processing of emotional memories. The authors hypothesized that it was through the dopamine receptors in the amygdala that this neurotransmission was taking place, therefore dopamine is required for the destabilization of “Pavlovian” memories.

Their results suggest that they might be correct.

… the results of the experiments reported here clearly demonstrate that dopaminergic signaling is a requirement for reactivation-induced memory destabilization. Destabilization and prediction error therefore have a shared dependence upon dopaminergic signaling, as a retrieved memory requires prediction error in order to destabilize… although we did not directly test the requirement for prediction error in destabilization in these experiments

For a memory that you already have, surprise (prediction error) is required to destabilize it (make it changeable) because of the dopamine that surprise releases.

It is still not clear if you can induce this destabilization via dopaminergic signaling alone, in the absence of prediction-error.

Now go lift something heavy,
Nick Horton

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