The Science of Stage Fright: How Stress Causes ‘Brain Freeze’

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When presidential candidate Rick Perry froze during a recent GOP debate — unable to remember the name of a government agency he wanted to eliminate — his brain was clearly under stress. Now new research helps explain why at moments of peak pressure, virtually all of us are vulnerable to similar failures, finding it harder to recall key words at the right time and almost impossible to focus on the task at hand.

Earlier studies have shown that under high stress, the brain tends to shut off the cortical networks involved in creativity, contemplation, planning and thinking abstractly. While that sounds like a glitch, it’s actually a benefit — at least when you are facing physical threats. Taking time to consider your options is not advisable while being chased by a tiger or facing enemy fire.

As the authors of a new study in Science put it, acute stress “sharpens our senses, creates a state of fearful arousal and strengthens our memories of stressful experiences but impairs our capacity for slow deliberation.”

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For the new paper, researchers led by Erno Hermans of New York University recruited 80 healthy adults and subjected them to emotional stress, induced in this case by showing them extremely violent fight scenes from Gaspar Noe’s film Irreversible. The researchers monitored the participants’ physical stress response and used brain scans to examine the regions that were activated while people watched the scenes.

None of the participants were regular viewers of violent films or players of violent videogames. Half of them saw the violent clips first, followed by neutral scenes from another movie; the other half saw the clips in the reverse order.

As expected, the violent images produced emotional distress, raised participants’ levels of the stress hormone cortisol and elevated their heart rates. In the brain, the most active regions were part of the “fight or flight” network, including areas that monitor the body’s internal state, regions involved with fear and other emotions, and those involved with orienting attention. The more cortisol released, the greater the strength of the signaling seen in this network. Meanwhile, the parts of the prefrontal cortex involved in thought and reasoning began to shut down.

That means, basically, that under stress, the brain automatically shifts its focus away from current activity — for example, doing homework or debating — and toward readiness for fight or flight. That’s why high stress can “make your mind go blank” at the worst possible moments. A faster but more primitive neural network takes over.

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The researchers conducted a second experiment to determine which brain chemicals may be most responsible for the shift of the brain’s activity into the fight-or-flight response. Interestingly, they found that, despite correlations between the brain’s stress response and levels of cortisol seen in the first part of the study, participants who were given a drug that prevents the synthesis of cortisol showed no reduction in stress-induced brain activity.

However, when people received the drug propranolol — which is used to treat high blood pressure, fight tremors and combat stage fright — it did mitigate the increase in network activity. Propranolol reduces the activity of the neurotransmitter noradrenaline, also known as norepinephrine, which is a critical component of the stress response.

Similar noradrenaline-reducing treatments like clonidine are sometimes used to treat children with emotional stress, whose symptoms of distraction can mirror those of attention deficit/hyperactivity disorder. (Changing children’s stressful situations also helps, of course, if possible.) Incidentally, use of the drug propranolol is banned in the Olympics because of its anxiety- and tremor-reducing effects.

The results of the new study further suggest that the drug may improve performance by preventing or reducing the strength of the “brain freeze” aspect of stress. Whether propranolol could provide an unfair edge in a presidential debate has not been determined. But, to my mind, anything that encourages clearer thinking among the candidates should definitely be allowed.

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Maia Szalavitz is a health writer at Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.