A Potential Cure for PTSD

Introduction

Currently, about 9 million individuals in the United States suffer from Post-Traumatic Stress Disorder (PTSD), a condition that stems from witnessing of experiencing a traumatic experience. Due to increasing knowledge of the brain, scientists are embarking on manipulating memories for good - weakening traumatic memories. In a paper published in the scientific journal Nature, Whitmore et al. experimented with sleep disruption on memories. Though the study did focus on the difference between the strength of new and old memories, the information discovered could be crucial in helping those with PTSD.

In sleep, especially during stages 2 and 3, the brain strengthens memories through solidation, in memories are reactivated, or, replayed. Additionally, memories could be transformed when the brain integrates several moments into a general memory (this is an interesting Ted-Talk that touches on a similar topic). Because memories are reactivated during sleep, disruption may make this process ineffective.

In a prior study, it was confirmed that memories formed shortly before sleep could be weakened by auditory stimulation. This process is called targeted memory reactivation with sleep disruption (TMR-SD). The study focused on the effect of TMR-SD on memories formed a week before attempting to disturb solidation (therefore, less fragile, older memories).

In order to test this, Whitmore et al. used two similar procedures:

1. Memories created a few minutes prior to sleep

2. Memories created a week prior to sleep

It was hypothesized that in older memories, TMR-SD would have little to no effect.

Methods

Participants were tasked with learning the locations of 74 different objects. Objects were first shown in their correct location while their corresponding sound played. Then, objects pop up on the screen in the middle and participants were tasked with moving the object to the correct location. If they were correct, the corresponding sound played.

In the second half of the learning stage, incorrectly placed objects were shown again and again until participants had matched all to the correct place. This helped with learning.

5 minutes after learning, participants took an initial test without any feedback or corresponding sounds, and instructed to sleep.

Figure 1. Experimental Procedure

When people were sleeping, scientists waited until stable stage 2 sleep to present sound cues and sounds were either quiet to not disturb sleep or loud enough to disturb sleep but not wake participants up. Post-nap, all 74 sounds were played and participants were asked if they heard any during sleep.

Figure 1. Experimental Procedure for the initial and delayed sessions

Results / Discussion

Results from the experiment favored the hypothesis that memory reactivation prompted by unobtrusive sounds (quiet to not disturb sleep) is beneficial to memory strengthening, but sounds that cause brief disruptions in sleep prevented memory consolidation.

However, while the sounds that disrupted sleep effectively reversed memory consolidation and degrades memories, older memories are barely affected. Therefore, it can be concluded that memories become more resilient with time: memory consolidation!

These findings have exciting real-world applications, especially for PTSD. For instance, traumatic memories, if recent, can be easily weakened through using related sounds to disrupt stage 2 sleep and prevent consolidation. Because memories that cause PTSD are strongly linked to sounds, scientists can use sounds (for instance, sirens or loud bangs) to target and weaken associated memories, but only if they are fairly recent.

In conclusion, the study confirms that sleep disruptions caused by sounds related to the targeted memory can weaken it. This expands the horizon of therapeutic interventions that work with the brain's processes.