One of the midbrain regions that Mobbs observed becoming active in humans when a “predator” was close is an area called the periaqueductal gray region. This area showed higher activity in the people who crashed into the walls more often, providing further evidence that it plays an important role in panic. Researchers have explored the anatomy of fear more directly in rats; by manipulating different areas of the rat brain, they are able to alter parts of the standard fear-driven sequence of behavior. When neuroscientists put electrodes into the periaqueductal gray region of rat brains and stimulated the neurons there, the creatures immediately started to run and jump uncontrollably.
The new research suggests that fear is not a single thing; rather, it is a complex, ever-changing strategy that mammal brains deploy to cope with danger. When a prey sees a predator at the distance, the prey powers up a forebrain network that primes its body, raising the heartbeat and preparing it for fast action, and it sharpens the brain’s attention to the outside world by evaluating threats, monitoring subtle changes, and running through possible responses. The forebrain network also keeps the midbrain network shut down so that, instead of fleeing at top speed, the prey keeps very still at first. As the predator gets closer, the forebrain’s grip on the midbrain loosens and it midbrain initiates a fight or flight response. At the same time, it shuts down the slower, more deliberative forebrain; this is not a time for thinking.