The U.S. has sent thousands of soldiers into combat over the past decade or so, and a good number of them have returned home with deep psychological scars. Up to 20 percent of Afghanistan and Iraq war veterans suffer from post-traumatic stress disorder, or PTSD, according to some expert estimates. Now researchers at The Picower Institute for Learning and Memory at Massachusetts Institute of Technology have found a class of drugs that show promise for helping to heal traumatic memories.

Psychologists often treat PTSD using behavioral therapy, a method that encourages patients to confront stressful memories and then replace those recollections with new, nontraumatic ones. But the technique is not always effective. Li-Huei Tsai and her colleagues tested drugs that they predicted might make a patient’s memories more responsive to therapy. The researchers targeted old and new traumatic memories in mice with drugs called histone deacetylase (HDAC) inhibitors, which increase the plasticity of the brain’s learning and memory areas. They found that HDAC, in combination with behavioral therapy, eased the burden of both recent and old stressful memories in mice, whereas behavioral therapy alone only helped mice suffering from recent trauma.

The image above shows the hippocampus (white dotted line) of a mouse treated for PTSD with both HDAC inhibitors and behavioral therapy (right) versus that of a mouse receiving only behavioral therapy. Researchers saw a higher rate of hippocampal metabolic activity (green and red)—which is a measure of learning capacity—in mice treated with both drugs and therapy, according to the study, which was published in the January 16 issue of Cell.

Tsai thinks the brain may store older memories in a less accessible region of the brain, and behavioral therapy alone might not coax those memories into the open for treatment. HDAC inhibitors, however, increase neuronal malleability so that psychologists can access older memories during therapy.

The M.I.T. researchers have only experimented with HDAC on mice, so they do not know whether the drugs will effectively treat people with PTSD. But if it turns out that the inhibitors work on humans, the new discovery will one day be a happy memory for those who suffered from PTSD.

—Annie Sneed