What Makes You Flinch?

Aug. 20, 2004 -- Don't even try to keep a poker face: All animals -- including humans -- instinctively flinch when they feel threatened.

Now, there is new information about what's going on when flinching takes place.

Flinching headquarters appears to be a "hot spot" in the brain, researchers Dylan Cooke and Michael Graziano of Princeton University's psychology department, find.

In tests on monkeys, Cooke and Graziano identified a region of the brain that they call the "polysensory zone" that appears to be involved in flinching. This region responds to various different stimuli -- visual, sound, and touch -- and may be involved in the physical behavior seen during a threat.

The duo gave the monkeys drugs to increase or decrease brain activity in the cells of the polysensory zones, and then tested their reaction to a mild puff of air directed at the monkeys' faces.

The drugs that increased brain cell activity prompted exaggerated flinching; the drugs that dulled brain cell activity reduced the monkeys' reactions.

Flinching happens in two phases. First, there is an initial startled reaction to stimuli -- the air puff. Next comes a longer defensive response designed to ward off the threat.

When the monkeys flinched, they squinted, blinked, lifted their upper lip, flattened their ears, turning the head away, and moved their hands, arms, and shoulders defensively (sound familiar?).

Drugs that reduced brain cell activity in the hot-spot zone only affected the second part of the flinch -- the longer phase (muscle movements) directed at avoidance of the threat.

The finding shows that the polysensory zone -- an area of the brain responsive to various stimuli -- alters muscle response along with the ability to process sensory stimuli.

They conclude that this area of the brain provides insight into the how our bodies function to defend itself.

The polysensory zone may specialize in reacting to objects that suddenly approach the body, or it may have other sensory and motor functions not tested in this experiment, write the researchers in the journal, Neuron.

SOURCE: Cooke, D. and Graziano, M., Neuron, August 19, 2004; vol 43: pp 585-593. News release, Neuron.