Scientists Take the Edge Off Bad Memories in Mice

Down the memory lane

Down the memory lane

Source: New York Times

AUG. 27, 2014

Memories and the feelings associated with them are not set in stone. You may have happy memories about your family’s annual ski vacation, but if you see a tragic accident on the slopes, those feelings may change. You might even be afraid to ski that mountain again.

Now, using a technique in which light is used to switch neurons on and off, neuroscientists at the Massachusetts Institute of Technology appear to have unlocked some secrets about how the brain attaches emotions to memories and how those emotions can be adjusted.

Their research, published Wednesday in the journal Nature, was conducted on mice, not humans, so the findings cannot immediately be translated to the treatment of patients. But experts said the experiments may eventually lead to more effective therapies for people with psychological problems like depression, anxiety or post-traumatic stress disorder.

“Imagine you can go in and find a particular traumatic memory and turn it off or change it somehow,” said David Moorman, an assistant professor of psychological and brain sciences at University of Massachusetts Amherst, who was not involved in the research. “That’s still science fiction, but with this we’re getting a lot closer to it.”

The M.I.T. scientists labeled neurons in the brains of mice with a light-sensitive protein and used pulses of light to switch the cells on and off, a technique called optogenetics. Then they identified patterns of neurons activated when mice created a negative memory or a positive one.

A negative memory formed when mice received a mild electric shock to their feet; a positive one was formed when the mice, all male, were allowed to spend time with female mice.

Later, mice that had been shocked were put in the company of females — a positive experience — while scientists used the light to activate the memory of the shock. As a result, the negative memory became less negative; the mice became less fearful in the place where they had been conditioned to remember the shock.

The mice that originally spent time with the females later received mild electric shocks while scientists activated the neurons associated with this positive memory. The memory became less enticing, the scientists concluded: the mice froze more and sniffed less, standard measures of fear and reward in rodents.

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