Our reaction speed varies over the course of a single breath, with a measurable advantage when we exhale.
Breathing seems automatic and independent of our thoughts. Yet the respiratory rhythm accompanies the activity of several regions of the brain. Previous research had already linked certain phases of breathing to memory, emotions, or perception. One team wanted to find out whether this cycle also changed how quickly we respond.
The experiment involved 35 adults. Participants had to react as quickly as possible to the appearance of a visual signal while their breathing was recorded. This allowed the researchers to determine whether each stimulus had appeared during an inhalation or an exhalation.
The average difference was 41 milliseconds in favor of exhalation. This may seem very short, but human reaction time itself is measured in just a few hundred milliseconds. The effect therefore represents a detectable variation on the scale of a rapid response.
The researchers also examined the precise timing within the respiratory cycle. Performance did not differ only between the two broad categories of inhalation and exhalation. The likelihood of responding quickly varied gradually with the phase of breathing, indicating a rhythm linked to the cycle itself.
Why would incoming or outgoing air alter our reaction? Breathing produces mechanical and neural signals that travel up to the brain. It also accompanies variations in brain activity. These oscillations could make certain networks temporarily more or less ready to process a stimulus and trigger an action.
The experiment does not show that deliberately exhaling systematically improves performance. Participants did not try to synchronize their breathing with the signal, which appeared unpredictably. Forced breathing could also alter attention and introduce other effects.
The study also involved a small group of adults and a very simple visual task. It remains to be seen whether the same difference appears during longer decisions, athletic movements, or situations in which several pieces of information must be processed at the same time.
The researchers can now test whether the effect changes with physical exertion, age, or different breathing rhythms. Brain activity measurements taken in parallel could also show which regions follow the breathing cycle at the precise moment a response is triggered.