With a flash of blue light, a team of researchers from the Massachusetts Institute of Technology have quelled an abnormal, repetitive behavior in mice, gaining powerful new insight into an errant brain circuit that may give rise to obsessive-compulsive disorder.
The study, published Thursday in the journal Science, uses a cutting-edge neuroscience technique called optogenetics to probe a mouse version of a disorder that affects 1 percent of adults in the United States. Optogenetics is less than a decade old, but the futuristic technique has rapidly transformed the field of neuroscience by giving researchers precise control over the brains of laboratory animals. Scientists insert a light-sensitive gene into specific brain cells, which they can then switch on or off with a pulse of light that is delivered through a cable implanted in the mouse’s skull.
“The exciting thing about these results is the second we turn on the light, the animal stops doing the abnormal thing. It’s immediate,” said Ann Graybiel, a neuroscientist at the McGovern Institute for Brain Research at MIT. “It’s a ‘You don’t believe your eyes’ sort of thing.”
Considerable ethical and technical issues would need to be resolved before optogenetics could be used as a therapy. But the knowledge it yields about how precise brain circuits are involved in disease could prove useful in the shorter term.
For example, deep brain stimulation is already being used in some patients with OCD, and it is possible that understanding the brain circuits involved could refine the placement and use of that technology.
Graybiel and colleagues found that obsessive grooming in mice can be caused by a lack of inhibition of a subcircuit in the brain. Mice genetically predisposed to exhibit obsessive behaviors learned to associate a tone with a drop of water falling on their nose a second and a half later — a trigger that caused them to obsessively wash their faces as soon as they heard the noise. But by turning on the light, researchers could flip on inhibitory brain cells, causing the mouse to stop grooming its face until the drop of water actually fell.