Switching the light on and off to switch OCD on and off.

Nature looks at some strange mice and even stranger methodology used to map their brains – by using light to turn OCD on and off:

Researchers have both created and relieved symptoms of obsessive-compulsive disorder (OCD) in genetically modified mice using a technique that turns brain cells on and off with light, known as optogenetics.

[Columbia neuroscientist Susanne] Ahmari’s team wanted to see if optogenetics could prompt repetitive grooming in mice — a commonly used equivalent sign of an OCD-like condition in animal models. The team injected viruses into the orbitofrontal cortex carrying genes for light-sensitive proteins. Certain nerve cells then began to produce the protein and became sensitive to light. The researchers then inserted an optical fibre to shine a light on these cells for a few minutes a day. It was only after a few days that they started to see the compulsive behaviour.

“Within a matter of a second or two, a behavioural change occurs,” says Ann Graybiel, who co-authored the MIT study. The abnormal grooming disappeared, leaving behind only the normal reaction to the water drop. “It’s phenomenal to watch,” Graybiel says.

She was doubly surprised that the cortex — the area associated with executive, even conscious control of behaviour — could be at the root of such an automatic response. “Everybody has thought that when we get these compulsive behaviours or really strong habits, then these behaviours reel off by themselves,” she says. Instead, the orbitofrontal cortex can send a ‘stop’ signal to other brain regions concerned with more automatic movements.

Ahmari thinks that the findings could be harnessed to help vanquish repetitive behaviours more quickly. She says that knowing how the brain changes over time to create repetitive behaviours could lead to better treatments. Nobody is suggesting, though, that humans should have optogenetic-enabling viruses injected into their brains as a therapy. “We’re not quite ready for that,” quips Graybiel.