Each week, we read what's going on the world of science and bring the wildest findings straight to you. Here's the latest:

Women’s sense of attraction to men changes when they’re on hormonal birth control

Women may be attracted to certain men because of their smell—a theory explored by so-called “smelly t-shirt” experiments, when women smell recently worn shirts and say which odors they’re most drawn to.

Previous research has suggested that hormonal birth control can interfere with this attraction, and change who women seek out as partners. A new study, out in Evolutionary Psychological Science, found that if women met their partners while on birth control, and then go off it, it can lead to a shift in their mate preferences and potentially lead to sexual or relationship dissatisfaction.

Women who are not on hormonal birth control are naturally drawn to the body odor of men who have different immune systems to their own, says first author Gurit Birnbaum, an associate professor at the Baruch Ivcher School of Psychology in Israel. A potential child would benefit from having parents with different immune systems, and so women have evolved to be sexually attracted to men with dissimilar immune systems, especially during high-fertility phases of their cycles.

“The larger the dissimilarity between mates' immune systems, the more threats the immune system [of the offspring] can combat,” Birnbaum says. Since hormonal birth control suppresses ovulation, a woman’s perception of a man may then change, and she may be attracted to or seek out a different partner.

On hormonal birth control, women could pick men who are cooperative and help with childcare instead of ones who are immune-compatible (not that they’re mutually exclusive). Women who were on hormonal birth control when they met their partners, and then later go off—which often happens when a couple decides to have a baby—may feel “disenchanted” with their partner choice, Birnbaum says.

“Prior studies have provided evidence for this hypothesis, indicating that women who had used hormonal contraceptives when they first met their partner and then ceased to take them experience lower levels of sexual and relationship satisfaction and are more likely to get divorced,” she tells me.

In the new study, three groups of women were compared: women who were on birth control when they met their partners, and then went off of it; women who were on birth control when they met their partners and were still taking it; and women who weren’t on birth control when they met their partners.

They found that the women who were on birth control and then stopped were more vulnerable to feeling desire for images of attractive men during high-fertility phases of their cycles, compared to the other women. “Still, it is unclear whether these women would have acted on their expressed desires and actually flirted with alternative partners,” Birnbaum tells me. “Indeed, people do not necessarily realize their fantasies or are even interested in carrying them out.”

How should women use this information? Birnbaum says she would recommend withholding pill use till you find a long-term partner, and use alternative non-hormonal contraceptives in the meantime. “Let your body choose the right partner for you without the hormonal interference induced by pills,” she tells me. (For short-term partners, it’s not as big of an issue.)

But at the very least, Birnbaum says, physicians should tell young women about these effects, while we continue to learn how much influence they have on relationships and love.

People with radical beliefs have a hard time knowing when they’re wrong

A lot of us may still be reeling from uncomfortable conversations around the holiday dinner table, and wondering why a certain relative refuses to budge on the latest divisive issue. A new study, published in Current Biology, looked at people who have radical beliefs—on both the right and left—and found one reason people are seemingly unable to have their minds changed.

The research examined something called metacognitive sensitivity, which is the ability to reflect on whether your beliefs and decisions are right, or feel appropriately confident in a decision. We would hope to feel more confident when we are correct, and less confident when we are wrong. Having too little or too much metacognitive sensitivity leads to problems—not being confident in right decisions, or being too confident in wrong ones.

Participants were shown two squares with flashing dots, and had to say which of the squares contained more dots. After, the subjects rated their confidence levels. The research found that people with radical beliefs, determined through questionnaires that tested for traits like intolerance to others’ viewpoints, dogmatic and rigid beliefs, and authoritarianism, had less metacognitive sensitivity.

Their confidence levels weren’t aligned with their actual performance, and they had higher confidence levels in their errors, and were less able to notice mistakes, says Max Rollwage, a PhD student in cognitive Neuroscience and Computational Psychiatry, and first author on the paper.

In a follow-up experiment, people were given more information about which square contained more dots, and allowed to change their confidence levels on their answer, if they had chosen wrongly. The people with radical beliefs still held onto their high confidence reports about their errors.

“In times of increasing political polarization and entrenchment of opinion, the ability to reflect on our viewpoints may be crucial for a fruitful discourse,” Rollwage tells me. “It is not yet clear whether reduced metacognition is the cause or consequence (or both) of radicalization, nevertheless it is easy to imagine that deficits in metacognition will contribute to the consolidation of radical beliefs.”

The good news? Rollwage says that other research from their lab has shown that metacognition can be improved through practice—it’s a skill you can learn, not a fixed trait. “Enhancing metacognition may provide an opportunity to counteract or prevent radical views,” he says.

Case report: A man’s treatment for depression gave him delusions

A 31-year-old man, referred to as Mr. A, was brought to the psychiatric emergency service at the University of Amsterdam after neighbors complained about his odd behaviors. Mr. A was convinced that brown spots on the wall of his living room were caused by asbestos and that his neighbors, the police, and his medical practitioners were scheming to kick him out of his house.

These delusions didn’t come out of nowhere: They were a result of an electrode placed deep into Mr. A’s brain to treat his depression. For nine years, Mr. A had tried antidepressants, psychotherapy, and electroconvulsive therapy, but his symptoms wouldn’t relent. He was unable to work, despite having a master’s degree, and was “extremely invalidated in daily life and suffered greatly,” says Ilse Graat, the first author on the paper, published in Brain Stimulation.

Mr. A qualified for an experimental treatment called deep brain stimulation, when an electrode is implanted into the brain to release electricity, and can target certain areas of the brain in different ways. DBS has been frequently used for movement disorders, like Parkinson’s, and it’s a relatively new treatment for psychiatric disorders, like OCD and major depressive disorder.

Graat and his co-authors reported that when they used a high current for the stimulation, Mr. A noticed his depressive symptoms going away. But then came his paranoid delusions. When his doctors lowered the current of the DBS, the delusions remarkably disappeared within hours. But, the depression symptoms came back. When they again increased the current, the delusions immediately returned.

The story of Mr. A reveals that DBS in certain parts of the brain, the nucleus accumbens in this case, may induce delusions. With such a new treatment, it’s important for us to learn and record any such side effects, Graat says, so we know about them for future patients. Also, stimulation side effects can be an interesting way to investigate the underlying causes of certain types of psychosis and delusions.

“We assume that in our patient, high-current stimulation of dopaminergic brain reward pathways may have instantaneously triggered overvalued ideas, that could be adjusted again by lowering the stimulation,” he says.

Your weekly health and science reads

Here’s what “millennial burnout” is like for 16 different people. By Anne Helen Petersen in Buzzfeed News.

If you haven’t read the widely-circulated article on millennial burnout and why it’s so hard to go to UPS and schedule appointments, do so now. When you’re done, check out this compilation of burnout experiences from people of all ages and races that Petersen collected, which reveals how widespread the feeling of burnout really is.

Why meeting another’s gaze is so powerful. By Christian Jarrett in BBC Future.

Full of interesting tidbits about eye contact. As I thought, there’s such a thing as too much eye contact–no one likes gazes longer than nine seconds, writes Jarrett (who also writes for this site).

Thank you for not eating your placenta . By Jennifer Gunter in The New York Times.

Turns out “placentophagy” is not an ancient practice.

What fullness is. On getting weight reduction surgery. By Roxane Gay in Medium.

A beautiful read on thinness, weight loss surgery, food, and the relationship to your body and hunger.

Why exercise alone won’t save you. By Vybarr Cregan-Reid in The Guardian.

Rather than joining a gym for this year’s resolution, maybe we should strive to make everyday life more active instead.