Friday Weird Science: Got PMS? Time to Spot the Snake!

Mar 09 2012 Published by under Friday Weird Science, Uncategorized

I got wind of this study on the twitters today, courtesy of Jennifer Oulette at Cocktail Party Physics. The instant I saw the words "snake" and "PMS", well, I knew where this was going.

Because ladies, the most important thing you need to know is that when you're PMSing, you will be a snake hunter extraordinaire!

N. Masataka & M. Shibasaki "Premenstrual enhancement of snake detection in visual search in healthy women" Scientific Reports, 2012.

(Even better than these badgers!)

The premise of this paper comes from trying to find ways to correlate behavior with PMS, and to them hypothesize as to why behavior might change specifically during PMS. Because all women suffer symptoms of PMS.

Although only roughly 30% of premenopausal women can be diagnosed with PMS on the basis of a variety of questionnaires and prospective daily ratings, it is also true that the overwhelming majority of all of healthy women experience some level of premenstrual symptoms during the luteal phase.

Translation: Let's face it, guys, they ALL crazy before they're on the rag, amirite?


The authors wanted to come up with a way of reliably connecting changes in behavior with premenstrual hormone changes. For this they chose a task to ascertain how quickly women could identify SNAKES.



The idea is that we're faster when identifying fear-associated stimuli (like, presumably, snakes) as opposed to safe stimuli (like flowers). The authors hypothesized that when women are in the luteal phase they experience more anxiety, and thus they would identify snakes faster than at other points in the menstrual cycle.

They got together 60 women (all right handed, none on contraceptives, all with regular periods for the last four months and not pregnant), and showed them snakes or flowers. They asked them to find the snake and timed how long it took. They tested them in the follicular phase (prior to ovulation, roughly the first 13 days of your cycle) and the luteal phase of their menstrual cycle. The luteal phase is the phase immediately following ovulation, and persists from roughly day 14 to day 28, when you menstruate (which is usually considered day 1 of the next cycle).

What they found was they women where indeed faster at identifying snakes in the luteal phase, than they were in the follicular phase.

You can see above that in the luteal phase (white bars), the time to identify snakes decreased.

Ok, so women are apparently faster at identifying snakes during the luteal phase. The authors suggest that this is because their anxiety levels are higher, because the luteal phase is "a time of increased possible pregnancy".

Of course, we could go into the idea of women identifying OTHER kinds of snakes during the fertile period:

But we're all more mature than that.

Anyway, the authors say that the women are experiencing increased anxiety and this is shown in how fast they detect snakes. Did they ask about increased anxiety? Or anxiety at all? No. They basically just assumed that all women must be feeling more anxious. While some women do exhibit increased anxiety during PMS, certainly not all do. They also blame increased hormone levels, as well as increased cortisol levels during the luteal phase, but did not screen the women for any of these things. They also did not confirm that the women were in the follicular or luteal phases using blood tests, they just asked them about the timing of their periods and plotted it from there. While this isn't a bad thing, it's also not particularly accurate, and even within an average 28 day cycle, the phases can be highly variable.

Further, why would the increased possibility of pregnancy matter? Snakes are snakes ALL the time, they do not become exceptionally dangerous (snakey?) when you have an increased possibility of pregnancy. If this were true, wouldn't pregnant women have the highest rate of all in snake identification? Why did they not test pregnant women? And why would women be especially good at identifying dangerous things at periods of high fertility? Presumably, you want to be able to identify dangerous things ALL the time, regardless of fertility. Dead is dead and nonreproducing, no matter what phase of the menstrual cycle you were in. And while snakes can certainly be venomous, that affects you AND a fetus (if it's there). Many aversions to things during early pregnancy are meant to protect the fetus specifically from things which the woman can usually tolerate just fine. But I have never yet heard of a fetotoxic snake.

So while I have no problem with women identifying the photos of snakes faster during the luteal phase, I don't think you can really conclude anything from that. There are many things that change during menstrual phase, including mood (on average), brain size, temperature, attention and cognitive function, etc. Heck, visual acuity could even change.

But it does occur to me that this could be a truly awesome way to make extra money during my luteal phase: snake hunting! We ladies could make some extra cash on the side hunting snakes during our luteal phases. And in these tough economic times, that's pretty good news.

Masataka, N., & Shibasaki, M. (2012). Premenstrual enhancement of snake detection in visual search in healthy women Scientific Reports, 2 DOI: 10.1038/srep00307

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