Scientists have succeeded in permanently erasing frightening memories in mice, an early step toward the development of treatments for people haunted by traumas they can’t forget.

According to a study in the journal Neuron this week, researchers genetically manipulated the brains of mice to overproduce a key enzyme that appeared to selectively wipe memories from the animals’ brains.

The enzyme, calcium/calmodulin protein kinase II (CaMKII), also is present in humans, making it a possible target for a drug to treat post-traumatic stress disorder and other psychological problems, scientists said.

According to the report, researchers from the Medical College of Georgia and East China Normal University in Shanghai trained the mice to associate environmental cues -- a specific tone and cage -- with an electric shock, and then looked to see what the animals could remember.


Ordinary mice learn to freeze in fear when confronted with those cues. The engineered animals, however, did not show fear when they were placed in the cage or heard the tone, a sign that they did not remember that those things meant a shock was coming.

To find out whether the memory loss was permanent, researchers gave the mice a drug that, in effect, reduced the amount of the enzyme to normal levels. The animals still failed to freeze when they heard the tone or saw the cage.

In a series of subsequent experiments, researchers discovered that they could selectively erase fearful memories related to the electric shocks while leaving other recollections -- for example, the fear of cat odor -- intact.

Study author Joe Z. Tsien, a neuroscientist at the Medical College of Georgia, cautioned that formidable obstacles stood in the way of translating the research into a human drug. The genetic engineering technique used in the mice cannot be used in people, he said.


In addition, there is currently no practical method of delivering additional enzyme to the human brain, he said.

--

denise.gellene@latimes.com