Researchers at MIT have identified a molecular mechanism that appears to control the formation of fears stemming traumatic events, a finding that could lead to a drug to treat people unable to live normal lives because of their fears.

In a report published online Sunday by the journal Nature Neuroscience, Li-Huei Tsai and colleagues said an enzyme called cdk5 facilitates extinction of fear that is learned from a particular incident and, in mouse studies, can be manipulated to eliminate that fear.

Emotional disorders such as post-traumatic stress and panic attack stem from an inability of the brain to stop experiencing fear associated with a specific incident or series of incidents.

In some people, disturbing memories don’t fade with time, and may even get worse.

About 8 percent of the population will experience PTSD symptoms at some point in their lives, and 5.2 million adults suffer from the disorder in any given year, according to the National Center for Post Traumatic Stress Disorder.

For the MIT study, Tsai, a professor of neuroscience in the Department of Brain and Cognitive Sciences, and his team studied mice that got mild foot shocks while they were in a certain environment and then, later, re-exposed to the same environment without getting shocked.

Mice genetically engineered with increased levels of cdk5 had more trouble letting go, or extinguishing, the memory of the foot shock and continued to freeze in fear in the setting associated with the shock.

But in mice that had inhibited activity of the molecule, the bad memory of the shocks seemed to have no effect once the mice learned they no longer needed to fear being shocked.

“Inhibiting the molecule facilitated extinction of learned fear in the mice,” said Tsai. “This data points to a promising therapeutic avenue to treat emotional disorders and raising hope for patients suffering from PTSD or phobia.”

Traumatic memories are also associated other psychiatric disorders such as depression, anxiety and obsessive compulsive syndrome.