Word: braine
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...taught rats to fear all kinds of things--from buzzers to lights--by giving them electrical shocks when they hear the buzzer or see the light. The animals quickly learn to fear the stimulus even in the absence of a shock. Then researchers destroy small portions of the rats' brains to see what effect that has on their reactions (an experiment that would be impossible to conduct in humans). By painstakingly matching the damaged areas with changes in behavior, scientists have, bit by bit, created a road map of fear as it travels through the rat's brain...
...journey begins when a rat (we'll get to humans later) feels the stress, in this case an electric shock. The rat's senses immediately send a message to the central portion of its brain, where the stimulus activates two neural pathways. One of these pathways is a relatively long, circuitous route through the cortex, where the brain does its most elaborate and accurate processing of information. The other route is a kind of emergency shortcut that quickly reaches an almond-shaped cluster of cells called the amygdala...
...while the amygdala is busy telling the body what to do, it also fires up a nearby curved cluster of neurons called the hippocampus. (A 16th century anatomist named it after the Greek word for seahorse.) The job of the hippocampus is to help the brain learn and form new memories. And not just any memories. The hippocampus allows a rat to remember where it was when it got shocked and what was going on around it at the time. Such contextual learning helps the poor rodent avoid dangerous places in the future. It probably also helps it recognize what...
...this point, the other half of the stress signal has reached the cortex, which confirms that there's a danger present and figures out that it's causing pain. Once the shock has warn off, a part of the brain called the prefrontal cortex sends out an all-clear message and lets the amygdala know that it's O.K. to stand down. At least it's supposed to. It seems that it's harder to turn off a stress response than to turn it on. This makes sense, in terms of survival. After all, it's better to panic unnecessarily...
Discovering this basic neural circuitry turned out to be a key breakthrough in understanding anxiety. It showed that the anxiety response isn't necessarily caused by an external threat; rather, it may be traced to a breakdown in the mechanism that signals the brain to stop responding. Just as a car can go out of control due to either a stuck accelerator or failed brakes, it's not always clear which part of the brain is at fault. It may turn out that some anxiety disorders are caused by an overactive amygdala (the accelerator) while others are caused...