Interfering With Traumatic Memories of the Boston Marathon Bombings

The Boston Marathon bombings of April 15, 2013 killed three people and injured hundreds of others near the finish line of the iconic footrace. The oldest and most prominent marathon in the world, Boston attracts over 20,000 runners and 500,000 spectators. The terrorist act shocked and traumatized and unified the city.

What should the survivors do with their traumatic memories of the event? Many with disabling post-traumatic stress disorder (PTSD) receive therapy to lessen the impact of the trauma. Should they forget completely? Is it possible to selectively “alter” or “remove” a specific memory? Studies in rodents are investigating the use of pharmacological manipulations (Otis et al., 2014) and behavioral interventions (Monfils et al., 2009) to disrupt the reconsolidation of a conditioned fear memory. Translating these interventions into clinically effective treatments in humans is an ongoing challenge.

The process of reconsolidation may provide a window to altering unwanted memories. When an old memory is retrieved, it enters a transiently labile state, when it's susceptible to change before becoming consolidated and stored again (Nader & Hardt et al., 2009). There's some evidence that the autonomic response to a conditioned fear memory can be lessened by an “updating” procedure during the reconsolidation period (Schiller et al., 2010).¹ How this might apply to the recollection of personally experienced trauma memories is uncertain.


Remembering the Boston Bombings

Can you interfere with recall of a traumatic event by presenting competing information during the so-called reconsolidation window? A new study by Kredlow and Otto (2015) recruited 113 Boston University undergraduates who were in Boston on the day of the bombings. In the first testing session, participants wrote autobiographical essays recounting the details of their experience, prompted by specific questions. In principle, this procedure re-activated the traumatic memory, rendering it vulnerable to updating during the reconsolidation window (~6 hours).

The allotted time for the autobiographical essay was 4 min. After that, separate groups of subjects read either a neutral story, a negative story, or a positive story (for 5 min). The fourth group did not read a story. Presentation of a story that is not one's own would presumably “update” the personal memory of the bombings.

A second session occurred one week later. The participants were again asked to write an autobiographical essay for 4 min, under the same conditions as Session #1. They were also asked about their physical proximity to the bombings, whether they watched the marathon in person, feared for anyone's safety, and knew anyone who was injured or killed. Nineteen subjects were excluded for various reasons, leaving the final n=94.

One notable weakness is that we don't know anything about the mental health of these undergrads, except that they completed the 10 item Positive and Negative Affective Schedule (PANAS-SF) before each session. And they were “provided with mental health resources” after testing (presumably links to resources, since the study was conducted online).

In terms of proximity, 10% of the participants were within one block of the bombings (“Criterion A” stressor), placing them at risk for developing of PTSD. Most (95%) feared for someone's safety and 12% knew someone who was injured or killed (also considered Criterion A). But we don't know if anyone had a current or former PTSD diagnosis.

The authors predicted that reading the negative stories during the “autobiographical reconsolidation window” would yield the greatest reduction in episodic details recalled from Session #1 (S1) to Session #2 (S2), relative to the No-Story condition. This is because the negative story and the horrific memories are both negative in valence [although I'm not sure of what mechanism would account for this effect].²

Specifically, we hypothesized that learning a negative affective story during the reconsolidation window compared to no interference would interfere with the reconsolidation of memories of the Boston Marathon bombings. In addition, we expected the neutral and positive stories to result in some interference, but not as much as the negative story.

The essays were coded for the number of memory details recalled in S1 and S2 (by 3-5 raters³), and the main measure was the number of details recalled in S2 for each of the four conditions. Other factors taken into account were the number of words used in S1, and time between the Boston Marathon and the testing session (both of which influenced the number of details recalled).

The results are shown in Table 1 below. the authors reported comparisons between Negative Story vs. No Story (p<.05, d = 0.62), Neutral Story vs. No Story (p=.20, d = 0.39), and Positive Story vs. No Story (p=.83, d = 0.06). The effect sizes are “medium-ish” for both the Negative and Neutral comparisons, but only “significant” for Negative.

I would argue that the comparison between Negative Story vs. Neutral Story — which was not reported — is the only way to evaluate the valence aspect of the prediction, i.e. whether the reduction in details recalled was specific to reading a negative story vs. potentially any story. I wasn't exactly sure why they didn't do an ANOVA in the first place, either.


Nonetheless, Kredlow and Otto (2015) suggest that their study...

...represent[s] a step toward translating reconsolidation interference work to the clinic, as, to our knowledge, no published studies to date have examined nonpharmacological reconsolidation interference for clinically-relevant negative memories. Additional studies should examine reconsolidation interference paradigms, such as this one, in clinical populations.

If this work was indeed extended to clinical populations, I would suggest conducting the study under more controlled conditions (in the lab, not online), which would also allow close monitoring of any distress elicited by writing the autobiographical essay (essentially a symptom provocation design). As the authors acknowledge, it would be especially important to evaluate not only the declarative, detail-oriented aspects of the traumatic memories, but also any change in their emotional impact.


Further Reading

Brief review of memory reconsolidation

Media’s role in broadcasting acute stress following the Boston Marathon bombings

Autobiographical Memory for a Life-Threatening Airline Disaster

I Forget...


Footnotes

¹ But this effect hasn't replicated in other studies (e.g., Golkar et al., 2012).

² Here, the authors say:

...some degree of similarity between the original memory and interference task may be required to achieve interference effects. This is in line with research suggesting that external and internal context is an important factor in extinction learning and may also be relevant to reconsolidation. As such, activating the affective context in which a memory was originally consolidated may facilitate reconsolidation interference.

This is a very different strategy than the “updating of fear memories” approach, where a safety signal occurs before extinction. But conditioned fear (blue square paired with mild shock) is very different from episodic memories of a bombing scene.

³ Details of the coding system:

A group consensus coding system was used to code the memories. S1 and S2 memory descriptions for each participant were compared and coded for recall of memory details. One point was given for each detail from the S1 memory description that was recalled in the S2 memory description. Each memory pair was coded by between three to five raters until a consensus between three raters was reached. Raters were blind to participant randomization, but not to each other's ratings. Consensus was reached in 83% of memory pairs.

References

Kredlow MA, & Otto MW (2015). Interference with the reconsolidation of trauma-related memories in adults. Depression and anxiety, 32 (1), 32-7 PMID: 25585535

Monfils MH, Cowansage KK, Klann E, LeDoux JE. (2009). Extinction-reconsolidation boundaries: key to persistent attenuation of fear memories. Science 324:951-5.

Nader K, Hardt O. (2009). A single standard for memory: the case for reconsolidation. Nat Rev Neurosci. 10:224-34.

Otis JM, Werner CT, Mueller D. (2014). Noradrenergic Regulation of Fear and Drug-Associated Memory Reconsolidation. Neuropsychopharmacology. [Epub ahead of print]

Schiller D, Monfils MH, Raio CM, Johnson DC, Ledoux JE, & Phelps EA (2010). Preventing the return of fear in humans using reconsolidation update mechanisms. Nature 463: 49-53.