While the brain’s ability to form memories enables us to learn from our experiences and retain essential knowledge, there are occasions when this works to our disadvantage. Highly distressing episodes, for example, can lead to post-traumatic stress disorder (PTSD) if memories formed during such incidents become too deep-rooted, invading our consciousness with disturbing thoughts. However, according to a new study published in the journal Psychological Medicine, the administration of nitrous oxide – otherwise known as laughing gas – immediately following upsetting experiences may disrupt the encoding of these memories.
Exactly how memories form is still not fully known, although leading theories center on a process known as long-term potentiation (LTP), which occurs in two phases. The first of these, known as early LTP, involves the temporary stimulation of certain neurons involved in learning. While this does not lead to long-term memory retention, it does effectively "tag" particular events as worthy of being recorded during the second stage, or late-phase LTP.
This takes place while we are asleep, and involves the replaying of events as the neurons involved in early LTP repeat their activity patterns, leading to a strengthening of certain inter-neural connections, or synapses. This is thought to lead to the stabilization of memories as they become encrypted into the brain’s hardware.
The mechanisms by which these two phases occur are extremely complex, although one of the key pathways involves the activation of a type of receptor known as an N-methyl D-aspartate receptor (NMDAR). Because of this, researchers looking at ways to prevent the formation of stressful memories have tended to use substances that inhibit NMDAR.
Since nitrous oxide falls into this category, the authors of the new study decided to devise an experiment using the drug. To do so, they recruited 50 volunteers and asked them to watch a particularly graphic rape scene from the 2002 movie "Irreversible."
Following this, half of the participants were placed in a room containing nitrous oxide for half an hour, while the rest entered a room containing only air. Over the following seven days, they were required to make a note of how many “spontaneously occurring memories” of the rape scene they experienced. These are memories that “suddenly pop into your mind automatically,” and do not include deliberate thoughts about the film.
Nitrous oxide is often sold in small canisters as a recreational drug. Lenscap Photography/Shutterstock
While the number of flashbacks was roughly equal between the two groups on the first day, this frequency dropped significantly in the nitrous oxide group on day two, falling by more than half. The group that breathed only air, however, experienced only a slight decrease in spontaneous memories on day two, and took several more days before this frequency fell to the level of the laughing gas group.
Based on this finding, the researchers suggest that the memory of the rape scene was encoded less efficiently during the first night’s sleep in the nitrous oxide group, implying that the gas had somehow interfered with the LTP process.
Because the effects of the laughing gas would have worn off long before participants went to bed, the study authors conclude that it could not have had an impact on late-phase LTP, and must therefore have prevented the formation of memories by disrupting early LTP.
As such, they suggest that laughing gas may prove effective at preventing conditions such as PTSD if administered immediately following a distressing event. However, they also acknowledge that more work is needed to determine the efficacy and safety of using nitrous oxide for this purpose, since the drug is also known to cause dissociation, which refers to a distorted consciousness and sense of reality.