Facing Fears: Scientists Discover an “Off-Switch”

People dealing with phobias, anxiety, and post-traumatic stress disorder (PTSD) could soon be cured now that scientists have identified the brain’s regions that suppress fear response in mice.

“Our results challenge traditional views about learning and memory,” says Sonja Hofer, a neuroscientist at the Sainsbury Wellcome Centre and co-author of the study. “Our findings could also help advance our understanding of what is going wrong in the brain when fear response regulation is impaired in conditions such as phobias, anxiety, and PTSD.”

Some 100 mice were repeatedly exposed to the shadow of a bird, one of their instinctive fears. Researchers installed a barrier preventing mice from escaping. The animal eventually learned that the shadow posed no danger and did not attempt to flee once the barrier was removed. Throughout the experiment, specific neurons in the mice’s brains were silenced through optogenetics, a biological technique to control the activity of neurons or other cell types with light. Two brain parts play a crucial role in suppressing visual fears: the visual cortex (key in learning that certain things aren’t a threat) and – surprisingly – the ventrolateral geniculate nucleus (key in storing memories related to ignoring fears).