In post-traumatic stress disorder (PTSD) the trauma of the past — whether it is the experience of combat, sexual abuse or other deeply frightening event — comes to seem inescapable and as if it exists in the present. And though treatment has gotten better over the years, it could still be improved, especially since there’s no one method that has proven successful at relieving PTSD's intrusive thoughts, fears, and memories.

The key is finding a way to extinguish the stress response. Exposing PTSD patients to a certain type of gas as they’re recalling a stressful event may be one way to break the mental link between the memory and the experience of pain that comes with it, a new study suggests.

Each time an emotional memory is recalled, the brain actually restores it as if it were a new memory.

Researchers gave rats a shock to their feet along with a tone to condition a fear reaction. Later, when rats heard the tone alone, it triggered the same stress response — mainly freezing in place for several seconds — as the shock itself.

When the Harvard Medical School researchers exposed the rats to xenon gas shortly after hearing the sound alone for the first time, the fear response diminished, but the freeze response in the rats who didn’t inhale the gas persisted for up to two weeks longer.

The authors believe that what’s happening is that the gas is interfering with the consolidation process — when a memory is first remembered and is susceptible to change for a brief period.

Xenon gas is already used as an anesthetic in people and is known to block the brain’s NMDA receptors, which play a role in memory.

“We know from previous research that each time an emotional memory is recalled, the brain actually restores it as if it were a new memory,” said study author Edward G. Meloni in a news release. “With this knowledge, we decided to see whether we could alter the process by introducing xenon gas immediately after a fear memory was reactivated.”

An additional benefit of xenon gas is that its action on the brain is quite brief and concentrated — so it wouldn’t be likely to interfere with other types of memory in the brain.

“Unlike other drugs or medications that may also block NMDA receptors involved in memory,” said Meloni, “xenon gets in and out of the brain very quickly. This suggests that xenon could be given at the exact time the memory is reactivated, and for a limited amount of time, which may be key features for any potential therapy used in humans.”

Assuming the method would work for people, the gas would have to be administered as a person is recalling a traumatic memory in the psychiatrist’s office. Just as with the lab animals, the treatment would presumably break the pairing between the memory and the associated feelings of panic or fear. Then, a person’s PTSD might fizzle out, rather than reconsolidating over time.

The work will need to be expanded to determine its effectiveness, safety, and dosing, both in animals and in people. At least it’s promising that a treatment like this might be a reality some day, and that the array of tools to combat PTSD is steadily growing.

The study is published in the journal PLOS ONE.