the brains of 18 single young men seem to distinguish between the armpit smells of 5 similar-age ovulating women & the smells of an older group of 5 pregnant women. why we need to know this is anyone's guess.  

original article: Habel et al., 2021 (NeuroImage), image source

this story was in episode 3 #ovulation #pregnancy #smell #odour #FMRI

the error bar says

the most remarkable thing about this story is that it did NOT appear in any of the newspapers this week. yet this study is tabloid gold. i am starting to wonder whether science journalists check pubmed every week like the error bar does.

somewhere in Aachen, Germany, 5 ovulating and 5 pregnant women had 2 nights' worth of their underarm sweat mopped up and refrigerated.

these sweatpads were then placed under the noses of 18 young, single, heterosexual, cisgender men in a brain scanner while they looked at pictures of women's faces.

after inhaling the sweat for 3.5s, the single men rated the attractiveness of the pictures, or they guessed whether the depicted woman was pregnant or not (it was not mentioned if the women in this standard image database were pregnant or not).

the young men's attractiveness ratings or pregnancy guesses did not differ substantially after smelling the ovulating women's sweat compared to the pregnant women's or to a neutral one.

but the brain did seem to distinguish the women's armpits: after smelling the ovulating women's sweat, several regions in the, [checks notes], medial orbitofrontal cortex responded more than for the pregnant womens' pits.

can the brain smell ovulation?

the study seems to be a fairly standard, well-conducted brain imaging experiment - there's nothing obviously amiss in the methods or analysis, and the authors have been quite honest in laying out their hypotheses and finding that most of them were not supported.

so yes, on the face of it, the brain's orbitofrontal cortex - which seems to be the error bar's favourite brain area - does seem to distinguish between the sweats of ovulating and pregnant women.

while there were no strong differences in the attractiveness ratings of the photographs under the different smell conditions - photos were rated an average of '6' on the scale - the differences between conditions were in the hypothesised direction, so the behavioural part of this study may have been a bit underpowered.

the only obvious caveat about the study is that the 5 ovulating women who provided sweat were an average age of 24, while the 5 pregnant women were an average of 30 - and this is a substantial statistical difference. why such an obvious confound was not controlled in this expensive, quite invasive study, is not known. perhaps the brain can smell the age, rather than ovulation?

as for the brain imaging part: the error bar finds it intriguing that in the last episode the orbitofrontal and medial prefrontal cortex were associated with learning about reward, and in this episode it is associated with the perception of beauty in a meta-analysis of 49 studies, and the difference between ovulating and pregnant women in a single sweat-smelling study.

i think we've found St Valentines brain area.

let's hope the British tabloids do not find this study.


maybe. maybe it's age?

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