Researchers believe the link between nasal breathing and cognitive function has something to do with our sense of smell,
which evolved as a survival sense. In a 2018 study* published in the Journal of Neuroscience, researchers had participants smell several different scents, and then spend a period of time either breathing through their nose or their mouth for several minutes before asking them to recall what they had smelled. The group that breathed through their nose could recall what they had smelled with near-perfect accuracy, whereas the group that had breathed through their mouth performed significantly worse.
Want to read the study? See it here: