By Laura Beil
In less than one-tenth of a second
Your eyes spot a snake (or your ears pick up on footsteps behind you in an alley) and shoot a signal to the amygdala, the part of your brain that’s the hard drive of human emotion. “The amygdala’s role is to assign emotional valence,” says Professor Pankaj Sah, deputy director of research at the Queensland Brain Institute. “It tags things with an emotional content to your sensory world.” The brain cells trigger the adrenal glands – and just like that, your adrenaline rush is on, lending you added strength and speed.
The amygdala then prompts the already-busy adrenal glands to churn out cortisol, a stress hormone and part of your “fight or flight mechanism,” says Professor Sah. High levels of cortisol can impede insulin, causing a rise in blood sugar – that is, a little extra fuel to respond quickly.
Within three seconds
The amygdala triggers your autonomic nervous system, which encompasses the physical responses to fright, according to Professor Sah. Thanks to the adrenaline, you’re breathing faster (to take in extra oxygen), your heart is racing (to get that oxygen to your muscles), your appetite stalls (the energy your body would use for digestion is diverted toward survival), you’ve started to sweat (to keep from overheating) and your pupils are dilated (to better recognise an enemy).
Cortisol has saturated your bloodstream and feeds back into the amygdala to boost the perception of danger. It also reinforces your memory of the initial fright, so you may feel a little bit jumpy for the next few days.
Within five seconds
The rest of your brain is now fully tuned in to the threat. Nerve cells start to release endorphins. “They’re partly involved in pain circuits, so your response to pain can be dampened down,” says Professor Sah. These morphine-like natural painkillers can combat the effects of physical stress (just in case you get injured by the scary thing that’s revved you up).
Your brain is also releasing dopamine, the neurotransmitter best known for ushering in a “feelgood” sensation akin to what you’d get from some narcotics. Hence, that thrill-packed delight some people may feel while watching horror movies.
Within five minutes
Once the danger has passed, the amygdala will send a signal to your brain. “Your brain then evaluates what’s happening,” says Professor Sah. Your body starts to simmer down (you can help it along by taking slow, measured breaths). The thinking centre of your brain, the frontal cortex, was previously drowned out by all the fuss but is now able to unleash nerve signals that quieten the amygdala and talk sense into the rest of your head.Read more:
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