Breathing doesn't just fill our lungs with oxygen and help us stay alive, it could also affect the way we think and feel, according to a new study.
Researchers have discovered that the rhythm of our breathing creates electrical activity in the human brain, and the effect is slightly different depending on if we use our mouth or nose to breathe, and if we're inhaling or exhaling.
To find this link between brain activity and breathing patterns, researchers from Northwestern University analysed electroencephalography (EEG) data from seven epilepsy patients.
These patients had electrodes implanted into their brains prior to surgery to figure out the origin of their seizures, but the data also showed that their brain activity appeared to fluctuate in sync with their breathing.
This activity was seen in three areas of the brain: the piriform (olfactory) cortex, which processes smells; the hippocampus, which controls memory; and the amygdala, which is tied to emotional processing.
"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," says neurologist Christina Zelano.
"When you breathe in, we discovered you are stimulating neurons in the olfactory cortex, amygdala, and hippocampus, all across the limbic system."
The researchers found that the stimulation appeared to be limited to when the patients were inhaling, and only when breathing with their nose, not their mouths.
To investigate further, the researchers recruited 70 healthy participants aged between 18 and 30 for a behavioural experiment.
In the test, the participants had to make quick decisions to determine whether images of faces shown only for a split second expressed fear or surprise.
The aim was to get a closer look at how the amygdala – which is involved in interpreting the facial expressions – was affected by breathing in or out, and via the mouth or nose.
The team's results suggest that the participants were a fraction of a second quicker to recognise fearful faces during inhalation – but only if breathing in through their nose. There was no advantage at recognising surprised faces.
In a separate memory test designed to measure activity in the hippocampus, 42 of the participants were shown pictures of objects on a computer screen, and later asked to recall them.
In the test, the group did slightly better at remembering the objects when they were breathing in, rather than breathing out, recalling objects with around 5 percent more accuracy when inhaling via their nose.
We should point out that the researchers have only found a correlation here, and without further evidence and replication in a much larger sample, it's not clear what's exactly going on.
But the team suggests that our cognitive functions might be boosted by inhaling when we're in dangerous situations – a time when we might need to react to things more quickly or effectively, and our breathing naturally quickens.
"If you are in a panic state, your breathing rhythm becomes faster. As a result, you'll spend proportionally more time inhaling than when in a calm state," says Zelano.
"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."