The way we breathe may affect how well our memories are consolidated (i.e. reinforced and stabilised). If we breathe through the nose rather than the mouth after trying to learn a set of smells, we remember them better, researchers at Karolinska Institutet in Sweden report in The Journal of Neuroscience.

Research into how breathing affects the brain has become an ever-more popular field in recent years and new methodologies have enabled more studies, many of which have concentrated on the memory. Researchers from Karolinska Institutet now show that participants who breathe through the nose consolidate their memories better.

"Our study shows that we remember smells better if we breathe through the nose when the memory is being consolidated -- the process that takes place between learning and memory retrieval," says Artin Arshamian, researcher at the Department of Clinical Neuroscience, Karolinska Institutet. "This is the first time someone has demonstrated this."

One reason why this phenomenon has not previously been available for study is that the most common laboratory animals -- rats and mice -- cannot breathe naturally through their mouths.

For the study, the researchers had participants learn twelve different smells on two separate occasions. They were then asked to either breathe through their noses or mouths for one hour. When the time was up, the participants were presented with the old as well as a new set of twelve smells, and asked to say if each one was from the learning session or new.

The results showed that when the participants breathed through their noses between the time of learning and recognition, they remembered the smells better.

New method facilitates measuring activity in the brain

"The next step is to measure what actually happens in the brain during breathing and how this is linked to memory," says Dr Arshamian. "This was previously a practical impossibility as electrodes had to be inserted directly into the brain. We've managed to get round this problem and now we're developing, with my colleague Johan Lundström, a new means of measuring activity in the olfactory bulb and brain without having to insert electrodes."

Earlier research has shown that the receptors in the olfactory bulb detect not only smells but also variations in the airflow itself. In the different phases of inhalation and exhalation, different parts of the brain are activated. But how the synchronisation of breathing and brain activity happens and how it affects the brain and therefore our behaviour is unknown. Traditional medicine has often, however, stressed the importance of breathing.

"The idea that breathing affects our behaviour is actually not new," says Dr Arshamian. "In fact, the knowledge has been around for thousands of years in such areas as meditation. But no one has managed to prove scientifically what actually goes on in the brain. We now have tools that can reveal new clinical knowledge."

The study was financed by several bodies, including the Knut and Alice Wallenberg Foundation, the Swedish Research Council and the Netherlands Organization for Scientific Research, Ammodo Science Award.