For people who go though stressful events and just can’t seem to move beyond the anxiety they trigger, a new study may offer some answers. It turns out that there’s a chemical in the brain that’s responsible for the dissipation of anxiety – and if you don’t have enough of it, your anxiety may stick around too long.

"The memory of the terrible events is not just erased,” said study author Andras Bilkei Gorzo in a news release. "Those impacted [by stress] learn rather via an active learning process that they no longer need to be afraid because the danger has passed." People differ in both how active the channel is and how much it responds to input from other brain circuits.

The people with lower levels of dynorphin also had more persistent activity in the amygdala, the area of the brain that governs the stress response.

Most people are familiar with endorphins, the “feel good” chemicals that are released after intense exercise and are responsible for the runner’s high. In the same family of chemicals is a compound known as dynorphin, which is responsible for dampening the emotional response that is associated with stressful or traumatic events. Some people have a harder time than others stepping out of the emotional memory of these events, and it may be dynorphin that’s responsible for the difference.

First the team showed that mice who were bred not to express the gene for dynorphin had a prolonged stress response after being given unpleasant electric shocks. In other words, they remained anxious far longer after the shocks subsided than would be expected. Normal mice reacted to the shocks the same way early on, but as time passed, their stress reactions subsided at a normal rate.

Next the authors applied the same logic to human participants, whose levels of dynorphin vary naturally. People who had lower levels of the chemical kept reacting to unpleasant stimuli longer than people who had more of it. The people with lower levels of dynorphin also had more persistent activity in their amygdalas, the area of the brain that governs the stress response. Finally, they also had less “talk” between their amygdalas and the prefrontal cortex, which is responsible for conscious thought and executive function.

Coauthor Henrik Walter underlines that getting past stressful events isn’t a passive process – the brain is actually working hard to reconfigure itself after the event. "[T]he 'forgetting' of acquired anxiety reactions isn't a fading, but, rather, an active process,” he says, which may be facilitated by dynorphin.

Hopefully the results will lead to new treatments for post-traumatic stress disorder (PTSD) and perhaps for other anxiety disorders, which affect many millions of people across the world.

The research was carried out by a team at Universität Bonn, and published in the The Journal of Neuroscience.