The Alarm System

What happens in the brain when we are afraid? Remember the little red metal square on the school-room wall with a piece of glass that reads, “Break in case of fire”? Just as the school has a fire alarm, so, too, our brain has an alarm switch called the amygdala…When the fire alarm is activated at the school, its job is twofold: first to grab the attention of everyone in the building, and second to alert the 911 operator.

Like that fire alarm, the amygdala both releases attention-getting adrenaline from the adrenal glands to the brain, and it alerts a sort of 911 operator to send out an urgent call. The brain’s 911 operator is the hypothalamus, which is connected to the “radio tower” of the pituitary gland. Instead of radio waves, the pituitary gland transmits hormonal signals calling for the body’s emergency response, which comes from the adrenal glands; they’re the stress steroids known as glucocorticoids.

When emergency responders arrive at the school fire, there is a fire chief who assesses the extent of the blaze and how many responders are on the scene. When there are enough firefighters, the chief calls back to the 911 operator and reports that, even though the alarm is still going, the operator doesn’t need to send any more.

Back in the brain, hippocampal neurons are the fire chief. They have glucocorticoid receptors that recognize the rise in stress hormones and signal back to the 911 operator (hypothalamus) saying, “Okay, you don’t need to call any more responders (stress hormones).” Then, after the alarm has sounded, the brain’s administrator, which is the dorsolateral prefrontal cortex (DLPFC, the part of the brain right behind the forehead), acting much like the school principal, evaluates whether there is real danger or whether it was a false alarm. If the administrator determines there is real danger, the alarm gets louder. If the administrator determines that there’s been a “false alarm,” everything calms down.