Breathing continually through an open mouth can affect learning outcomes. Twenty subjects were studied to monitor brain wave changes during nose and mouth breathing.
Breathing through the mouth showed different brain activity patterns, compared to nose breathing, and these changes are related to cognitive regions.
The reason for this change seems to relate to the decreased oxygen saturation during mouth breathing, suggesting that when cognitive abilities are required, mouth breathing can act as one of the variables that cause different outcomes in brain activities.
Lee KJ, Park CA, Lee YB, Kim HK, Kang CK. EEG signals during mouth breathing in a working memory task. Int J Neurosci. 2020 May;130(5):425-434. https://pubmed.ncbi.nlm.nih.gov/31518511/
