Compulsive Behavior Halted in Mice with Light: New Treatment for OCD

What exactly causes compulsive behavior like obsessive hand washing and biting your fingernails? Scientists may have found out. By activating a brain circuit that controls compulsive behavior, they've shown that they can actually block the behavior in mice.

About one percent of U.S. adults suffer from OCD, the obsessive-compulsive disorder that can cause anxiety. Patients are usually given antidepressants or antianxiety drugs to cope with the disorder, but there are those who don't respond to the treatments. For this small percentage, a new alternative is being developed known as deep brain stimulation. This treatment delivers electrical impulses via a pacemaker implanted in the brain.

In order to see if they could control neuron activity and treat compulsive behavior, researchers used optogenetics. This particular technique uses light to control neuron activity, but isn't yet ready for use in human patients. Because of this, they decided to use mice.

First, the researchers trained mice, whose Sapap3 gene was knocked out, to groom compulsively at a certain time. More specifically, the mice were trained to start grooming when they heard a tone. This allowed the scientists the opportunity to try and interrupt this compulsion.   

After training the mice, the researchers used optogenetics, which allows them to control cell activity with light by engineering cells to express light-sensitive proteins. When the researchers stimulated light-sensitive cortical cells, which send messages to the striatum (a portion of the brain related to habits), the mice stopped their compulsive grooming almost completely.

"Through the activation of this pathway, we could elicit behavior inhibition, which appears to be dysfunctional in our animals," said Eric Burguiere, lead author of the paper, in a news release.

The researchers weren't done yet, though. They also tested the optogenetic intervention in mice as they groomed in their cages, with no conditioning cues. It turns that that the mice groomed much less than they did without the stimulation.

"This represents a major leap forward, both in terms of delineating the brain basis of pathological compulsive behavior and in offering potential avenues for new treatment," said Scott Rauch, the psychiatrist-in-chief of McLean Hospital who was not involved in the study, in a news release.

The findings are published in the journal Science.