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A cold plunge makes it easy to see. Prefrontal activity drops for the first twenty to thirty seconds, and the body is set to react physically, which can save a life when a car is coming. Most of the time, saying nothing is the best response. Then the prefrontal cortex slowly comes back online.
The same suppression happens when a person is tired, stressed, or drunk. It is part of why stress is harder to handle late at night and why impulse control is way worse after a bad night of sleep. People with frontal damage lose top-down inhibition, the ability to feel an impulse and resist it, and sometimes turn violent or say inappropriate things.
Cold water in a controlled setting floods the system with adrenaline and norepinephrine, and staying thoughtful through that carries over to moments when something else triggers adrenaline.
Why does stress switch off the prefrontal cortex?
Yale neuroscientist Amy Arnsten has shown in animal studies that high levels of norepinephrine and dopamine impair prefrontal networks. The chemicals act on receptors that weaken the connections neurons use to hold information. At the same time, older, faster circuits in the amygdala and basal ganglia grow stronger. The brain trades careful thought for speed.
How do frontal injuries change behavior?
The classic case is Phineas Gage, a Vermont railroad foreman who survived an iron rod through his frontal lobe in 1848. Accounts from his doctor describe a man who became impatient and profane after the injury. Modern studies of patients with frontal damage describe the same loss of restraint. Neurologists treat Gage's case as an early clue that the frontal lobes govern social behavior.
Why is impulse control worse when tired?
In a 2007 study from Matthew Walker's lab at Berkeley, brain scans of people who had gone a night without sleep showed about 60 percent more activity in the amygdala in response to upsetting images. The links between the amygdala and the prefrontal cortex were weaker in the same volunteers. Without that top-down brake, emotional reactions ran stronger. The study was published in Current Biology.
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