Note that the experimental blocks were short, in the order of a few minutes, and was mixed between both nasal and oral breathing. Now imagine that whatever caus

Note that the experimental blocks were short, in the order of a few minutes, and was mixed between both nasal and oral breathing. Now imagine that whatever cause can spread that rapidly to the brain and have a noticeable effect there. Then orally breathing a full day (which is quite common when you have a cold) would lead to total cognitive degradation. You'd need a very peculiar mechanism to explain why that wouldn't happen.