A traumatic experience can trigger recurring intrusions.
Post-traumatic stress disorder (PTSD) is common after a catastrophic event, affecting around 5% of men and 10-12% of women at some time in their lives. Rates are particularly high among rape victims, 60-80% of whom will experience PTSD.
PTSD may feature "intrusions," involuntary, often distressing, memories that spontaneously come to mind after a distressing event.
Intrusions differ from flashbacks, which are intense and multi-sensory. In a flashback, a person may re-experience a traumatic event in full as though it were happening and may be unable to distinguish it from the present reality.
Researchers, led by Dr. Ravi Das of University College London in the UK, wanted to see if nitrous oxide would have any impact on the occurrence of intrusions following a trauma. The study involved 50 healthy adult volunteers and was overseen by both a trained clinical psychologist and a medical doctor.
They invited participants to watch two graphic scenes from the 2002 movie, "Irreversible," once described as "so violent and cruel that most people will find it unwatchable."
In previous studies, the chosen clips had created a much milder form of the intrusive memories that hound victims during the period after a real-life trauma.
Sharper fall in intrusions among those who received nitrous oxide
After watching the clips, the participants were given a gas to breathe for 30 minutes. Half of them breathed a 50-50 mix of nitrous oxide and oxygen; the others received medical air.
Over the following week, the participants kept a daily record of intrusions related to the movie clips.
Inhaling nitrous oxide after watching the clips was linked to a much faster decline in the incidence of distressing memories. The day after viewing, the number of intrusions fell by 50%, and intrusions declined exponentially over the following week. In contrast, the people who breathed normal air experienced a slower, more gradual and linear decline. A significant drop did not occur until day four.
Dr. Das says: "We think that this is because nitrous oxide disrupts a process that helps permanent memories to form."
"On any given day, your brain will be exposed to a huge amount of information, some important, but most trivial. If information is 'important' enough to remember, for instance because it produces a strong emotional response, it is 'tagged' for storage."
Tagging is carried out during the day by N-Methyl D-Aspartate (NMDA) receptors in the brain. Tagged information is then filed for long-term storage as we sleep.
Nitrous oxide blocks NMDA receptors, which may mean that it hinders tagging and leaves weaker memories.
Researchers also used questionnaires to assess participants' level of dissociation following the traumatic event.
Dissociation is a symptom of post-traumatic stress disorder (PTSD). It implies a sense of detachment from a situation and from oneself, of disconnection from one's body, a distorted idea of time and a feeling that things are unreal and dream-like.
Results showed that participants who felt more dissociated after watching the movie also experienced more intrusive memories.
In patients with dissociation, nitrous oxide could increase intrusions
However, nitrous oxide is known to induce a dissociative experience, so it could trigger worse intrusions among people who already feel dissociated following a traumatic event.
Fast facts about PTSD
- PTSD can result from a catastrophic event, witnessing injury or death, or losing a loved one
- Physical symptoms include difficulty breathing, pain and symptoms of shock
- Cognitive symptoms include confusion, disorientation, bad memories and nightmares.
As senior author Dr. Sunjeev Kamboj explains, nitrous oxide is commonly used as a painkiller in an emergency setting, because it is safe and easy to administer. Many people who find themselves in an ambulance or in the emergency room are likely to be experiencing some degree of psychological trauma.
Nitrous oxide is likely, then, to have some effect on the processing of that trauma in the victim's brain. It may either increase or decrease the likelihood of developing PTSD, depending on how dissociated the patient feels before taking it.
The authors emphasize the need for further research to establish whether dissociation affects trauma victims who receive nitrous oxide or other painkillers such as ketamine in the same way.
They also point out that volunteers in this study received nitrous oxide continuously for 30 minutes, while trauma patients will receive varying amounts.
Some may only receive small doses in the ambulance, whereas others could be breathing it on-and-off for hours in a hospital bed. Any effects, positive or negative, are also likely to vary depending on the dose.
To put things into perspective, the authors point out that the amount of nitrous oxide used recreationally in a balloon, for example, would probably not be enough to impact memory formation.
Medical News Today reported last year that PTSD can lead to premature aging