Researchers find inhalation, but not exhalation, may boost memory recall and fear response.
In a study published in the Journal of Neuroscience, researchers reveal how breathing synchronizes activity in the human brain, producing varying effects on memory and fear response - dependent on whether one inhales or exhales.
Lead author Christina Zelano, assistant professor of neurology at Northwestern University Feinberg School of Medicine in Chicago, IL, and colleagues first came across the link between breathing and brain activity after analyzing seven patients with epilepsy.
A week before these patients were due to undergo brain surgery, their brain activity was measured via electrodes implanted into their brains, with the aim of pinpointing the source of their epileptic seizures.
On looking at the data, the team found that the patients' brain activity changed with breathing, particularly in brain regions involved in the processing of odor, emotions, and memory - namely the olfactory cortex, amygdala, and hippocampus.
As a result, the researchers wanted to further investigate whether there is a link between breathing and cognitive functions linked to these brain regions - specifically, fear response and memory recall.
Inhalation through the nose may boost fear response
For their study, Zelano and colleagues recruited around 60 subjects and asked them to take part in experiments that tested memory function and fear response.
For the first experiment, participants were shown pictures of faces representing either fear or surprise and asked to quickly indicate which emotion was being expressed.
The subjects' breathing patterns were measured during the experiment.
The researchers found that when participants inhaled, they were able to recognize fearful faces faster than when they exhaled, though this was not the case with surprised faces.
However, when the subjects performed the same task just by breathing through their mouths, subjects were no quicker at identifying fearful faces, suggesting that only inhalation through the nasal passage boosts fear response.
"If you are in a panic state, your breathing rhythm becomes faster," explains Zelano.
"As a result you'll spend proportionally more time inhaling than when in a calm state," she adds. "Thus, our body's innate response to fear with faster breathing could have a positive impact on brain function and result in faster response times to dangerous stimuli in the environment."
Better memory recall with nasal inhalation
In another experiment, the participants were presented with pictures of different objects on a computer screen, which they were asked to remember. Later on, subjects were asked to recall the images.
The researchers found that the subjects were better able to recall the images when they inhaled, compared with when they exhaled.
Similar to the previous experiment, the link between better memory recall and breathing disappeared when subjects were breathing through the mouth.
All in all, the authors believe their findings suggest breathing is not just necessary for oxygen, but that it also plays a role in brain activity and behavior.
"One of the major findings in this study is that there is a dramatic difference in brain activity in the amygdala and hippocampus during inhalation compared with exhalation. When you breathe in, we discovered you are stimulating neurons in the olfactory cortex, amygdala and hippocampus, all across the limbic system."
What is more, Zelano says their findings may shed light on the mechanisms underlying meditation practices that involve focused breathing techniques.
"When you inhale, you are in a sense synchronizing brain oscillations across the limbic network," she adds.