al0ha writes "Fear begins in your brain, and it is there — specifically in an almond-shaped structure called the amygdala — that it is controlled, processed, and let out of the gate to kick off the rest of the fear response. In this week's issue of the journal Nature, a research team led by scientists at the California Institute of Technology has taken an important step toward understanding just how this kickoff occurs by beginning to dissect the neural circuitry of fear. In their paper (abstract), these scientists ... describe a microcircuit in the amygdala that controls, or 'gates,' the outflow of fear from that region of the brain. The microcircuit in question, [Professor David J. Anderson] explains, contains two subtypes of neurons that are antagonistic — have opposing functions — and that control the level of fear output from the amygdala by acting like a seesaw. 'Imagine that one end of a seesaw is weighted and normally sits on a garden hose, preventing water — in this analogy, the fear impulse — from flowing through it,' says Anderson. 'When a signal that triggers a fear response arrives, it presses down on the opposite end of the seesaw, lifting the first end off the hose and allowing fear, like water, to flow.' Once the flow of fear has begun, that impulse can be transmitted to other regions of the brain that control fearful behavior, such as freezing in place."