Reaction Times Slowed During Inhalation, Study Finds

Reaction Time Lagged at the Top of the Breath

Reaction times on a short alertness test slowed down around the peak of inhalation, according to a new Northwestern University study of 35 adults. Responses came faster while breathing out and during the brief pauses that naturally fall between breaths. Breathing is so automatic that most people never notice it, yet it may nudge how quickly the brain and body respond from one moment to the next.

Participants pressed a key the instant a red square turned yellow while sensors tracked every breath. The pattern held up in two separate experiments, one built around a night of sleep and one around an afternoon nap.

That raises a possibility: deliberately timing a breath before a high-stakes moment, such as a race start, might help. This study did not test that idea, and the findings come from a laboratory, not a sports field or a highway. They were published in the journal iScience.

Reaction Time Was Slowest Around the Peak of Inhalation

Researchers studied 35 healthy adults ages 18 to 33, with an average age of about 21. Twenty-two were female. All were right-handed and reported no neurological or sleep disorders. Ten took part in the first experiment and 25 in the second.

Each participant sat at a computer and watched a red square. Whenever it turned yellow, the task was to hit the space bar as fast as possible. Waiting times between color changes were randomized, so the flash could not be predicted. This three-minute test is a standard measure of sustained attention, the kind needed on a long, monotonous drive, and each session averaged roughly 47 trials. Meanwhile, a small tube near the nose recorded breathing, which averaged about one breath every four seconds. Exhales lasted longest, so roughly half of all trials landed on one. That let researchers sort every trial into one of three categories: breathing in, breathing out, or pausing between breaths. Participants received no instructions about how to breathe during the test, though they had practiced a breathing-training task at home between lab visits.

In the first experiment, participants took the test in the evening and again the next morning, after eight hours in bed at the lab. In the second, participants took it before and after a 90-minute afternoon nap period.

Reactions were slower when the yellow square appeared during an inhale than during an exhale or a pause, while exhales and pauses came out about the same. Average reaction time across the study was about 307 milliseconds, a little under a third of a second.

A closer analysis cut each breath into 20 equal slices. The slowest responses clustered at the top of the inhale, about 41 milliseconds (four-hundredths of a second) behind the fastest slice.

Researchers also checked whether participants grew more ready as the wait for the next flash stretched on. Responses after the shortest waits were the slowest, but breathing phase still predicted reaction time after that was taken into account.

Not everyone followed the trend. Eight participants reacted faster during inhales than exhales, while 27 showed the main pattern. Statistically, the two groups did not differ from each other, and the authors noted that individual differences might explain the variation.

Breathing May Shape Reaction Time Through Attention-Related Brain Regions

Brain regions involved in sustained attention include areas whose activity syncs with breathing, according to earlier work in rodents and humans. The authors suggest that breath-linked activity there may nudge response speed up or down from moment to moment. Only behavior and breathing were analyzed in this report, so that explanation remains a hypothesis. Because the same test is often used to gauge the effects of sleep loss, the authors said it would be worth checking whether the pattern holds under sleep deprivation.

Earlier studies of memory and emotion recognition found better performance during inhalation, which looks like a contradiction. Authors proposed that task type matters. Simple, reflexive tasks like this one may favor exhaling, while tasks that combine outside information with internal thoughts may favor inhaling. Another study found the favored phase can depend on which side of the visual field a target appears in, so no single rule seems to cover every situation.

Pauses got their own category here, something many earlier studies skipped or excluded. These were natural pauses, not deliberate breath holding, and the authors said they appear to affect thinking differently from inhalation and deserve continued study.

Tens of Milliseconds of Reaction Time Can Matter Outside the Lab

Gaps this small are easy to dismiss, but the authors argued against that. Starting reaction times among elite sprinters typically differ from one another by only a few tens of milliseconds, yet small variations in start time can predict final race outcomes. Tens of milliseconds can also make the difference in avoiding a traffic collision, according to the authors.

One reasonable-sounding assumption holds that breathing has no say in thinking as long as the oxygen keeps flowing, a view the authors say faces evidence to the contrary. This study adds to that evidence, and breathing earns a place in future research on attention.

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Disclaimer: This article summarizes a single peer-reviewed study for general information only. It is not medical advice. Consult a qualified professional before changing breathing habits or health routines.

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