We usually breathe through the nose, but switch to mouth breathing when we have a cold or during intense exercise. Swedish and Dutch scientists explored these two ways of breathing in order to determine which one was more beneficial to memory formation. Specifically, the research focused on olfactory memory consolidation.

Three main steps are involved in memory: encoding, consolidation, and retrieval. Encoding involves the ability to acquire new information from our senses. Consolidation allows us to maintain memories over time. Finally, through retrieval, we can extract and recall previously learned and stored information. Many studies have already highlighted the role of breathing in the process of memorization. For example, we know that in mammals, breathing rate has an impact on the information transfer between sensory networks and memory. Of course, it’s rather difficult to distinguish the effects of nose and mouth breathing in laboratory animals (mice and rats) since they don’t naturally breathe through their mouths.

It has already been shown that, for humans, breathing through the mouth reduces memory encoding and retrieval performance. In contrast, breathing through the nose causes neuronal oscillations that improve these processes. Artin Arshamian and his colleagues hypothesized that similar effects should be observed in the intermediate stage of consolidation. For their study, they examined the effect of breathing on the consolidation of episodic olfactory memory (part of long-term memory).

In the central nervous system, processing of olfactory information occurs first in the olfactory bulb which then sends it on to the piriform cortex where it is propagated further downstream to the hippocampus (a key area for memory). For their experiment, the scientists set up two separate sessions, each comprising the three phases of memory. In the first step (encoding), they asked volunteers (men and women) to memorize 12 smells, of which 6 were considered "familiar" (e.g. strawberry) and 6 were considered to be unknown (butanol, for example). In the second step (consolidation), the participants rested for an hour while breathing either only through the nose or only through the mouth. Finally, each group was again presented with the smells from the first stage of experiment with the addition of 12 new smells (6 familiar and 6 unknown). The goal was to tell whether each smell was old or new.

The results of the experiment were unequivocal: odor recognition was much better in subjects who used nasal consolidation when compared to those who breathed through their mouths (mouth consolidation). According to the authors: “These results provide the first evidence that respiration directly impacts consolidation of episodic events, and lends further support to the notion that core cognitive functions are modulated by the respiratory cycle.”

But it's winter now and I'm writing this article with a stuffy nose. I hope I’ll still be able to remember this study a few months from now!