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Found in a mouse: the brain’s “face your fear” center

The discovery, in mice, of a pair of nerve clusters regulating fearful versus bold responses to a visual threat could help people with excessive anxiety, phobias or post-traumatic stress disorder lead more normal lives.

I suppose some mice could suffer from anxiety or phobias or post-traumatic stress disorder, although how one might prove this is over my head.

Be that as it may, there are plenty of real threats in a mouse's world, not the least of them emanating from overhead. Evolution has smiled on mousedom by endowing its constituents with an innate fear of airborne predators, which speeds up their reaction time. That's a good thing for a little mouse, because sometimes it needs to think fast, as I noted in a news release about a new study published in Nature:

When a mouse in an open field perceives a raptor overhead, it must make a split-second decision to either freeze, making it harder for the predator to detect; duck into a shelter, if one is available; or to run for its life.

There is, it should be said, an additional option: stand up and fight like a . . . well, like a mouse.

Mice do fight, mainly among themselves. But mice threatened by the approach of an aerial predator will on very rare occasions — and almost always after finding a reasonably safe place — exhibit a display ordinarily reserved for signaling intraspecies aggression: It will stand its ground and thump its tail repeatedly against the ground (or alternatively, in this study, the floor or wall of its enclosure), in effect telling the predator: "Come get me, feather-brain!"

In the new study, a team directed by Stanford neuroscientist Andy Huberman, PhD, unraveled the brain circuitry that fine tunes the fright-flight-or-fight response to a visually perceived threat.

Smack-dab in the middle of every mouse's head — and probably yours, too — are a couple of tiny nerve clusters, one of them nestled tightly inside the other one, that send signals to different brain centers responsible for regulating reactions to sudden threats. Stimulating activity in one of those clusters elicits a timid action such as freezing in place or hiding out. Activate the other cluster, and the ordinarily rare tail-thumping bravado becomes the dominant response.

There's every reason to think people's brains possess equivalent circuitry, Huberman told me when I talked to him about the study. I wrote:

So, finding ways to noninvasively shift the balance between the signaling strengths of the two [nerve clusters] in advance of, or in the midst of, situations that people perceive as threatening may help people with excessive anxiety, phobias or post-traumatic stress disorder lead more normal lives.

If you're curious about how this might be accomplished, check out "The Fearful Eye," an article in our magazine, Stanford Medicine, about my episode of voluntary service as a guinea pig (not exactly a mouse, but close) in a virtual-reality experiment designed to evoke fear via immersion in 360-degree visual simulations of exposures to sharks, spiders and snapping pit bulls.

Photo by Taton Moïse

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