At the Winter Olympics, skiers, bobsledders, speedskaters and many other athletes all have to master one critical moment: when to start. That split second is paramount during competition because when everyone is strong and skilled, a moment of hesitation can separate gold from silver. A competitor who hesitates too much will be left behind – but moving too early will get them disqualified.
Though the circumstances are less intense, this paradox of hesitation applies to daily life. Waiting for the right moment to cross the street, or pausing before deciding whether to answer a call from a number you don’t recognize, are daily examples of hesitation. Importantly, some psychiatric conditions such as obsessive-compulsive disorder are characterized by impulsivity, or a lack of hesitation, while excessive hesitation is a crippling consequence of several anxiety disorders.
As a neuroscientist, I have been working to uncover how the brain decides when to act and when to wait. Recent research from my team and me helps explain why this split-second pause happens, offering insight not only into elite athletic performance, but also how people make everyday decisions when the potential outcome isn’t clear.
We found that the key to hesitation is a response to uncertainty. This could be where a dropped hockey puck will land, when a race starts, or placing your order at a new restaurant.
Every millisecond counts when the competition is fierce.
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Hesitation and the brain
To understand how the brain controls hesitation, my colleagues and I designed a simple decision-making task in mice.
The task required the mouse’s brain to interpret signals that were predictably good, predictably bad or – most importantly – uncertain, meaning somewhere in between. Different auditory tones indicated whether a drop of sugar water would soon be delivered, not delivered, or had a 50/50 chance of delivery.
How the mice behaved would not affect the outcome. Nevertheless, mice would still wait longer before licking to see whether a reward had been given in the uncertain scenario. Just like in people, unpredictable situations led to delays in response. This hesitation was not the result of vacillating between options in indecision, but an active and regulated brain process to pause before acting due to environmental uncertainty.
When we examined neural activity associated with the onset of licking, we identified a specific group of neurons that became active only when outcomes were unclear. Those neurons effectively controlled whether the brain should commit to an action or pause to gather more information. The degree to which these neurons were active could predict whether mice would hesitate before making a decision.
To confirm that these neurons played a role in controlling hesitation, we used a technique called optogenetics to briefly turn these brain cells on or off. When we activated the…
