【推荐1】Is it possible for the human heart to shrink (缩小) and if so, how does this change impact the human body?

Recently, scientists have discovered an unexpected similarity between long-distance swimming and spending a long duration of tire in space—both can cause the human heart to shrink over time! These findings were based on the experiences of astronaut Scott Belly, who spent 340 days in space in 2015, and Benoit Lecomte, an athlete who in 2018 swam 1,753 miles (about 2,821 km) across the Pacific Ocean in 159 days.

The absence of gravity in space means that the heart does not have to work as hard to pump blood through the aorta (主动脉), the largest blood vessel that supplies oxygen to all parts of our body. As a result, the heart loses muscle mass, causing it to reduce in size. The study was conducted by Benjamin Levine, a professor of internal medicine at the University of Texas South western Medical Center. He noted that the shrinkage was seen despite the fact that Scott Belly exercised every day.

Activities such as long-distance swimming can cause the heart to change similarly. Lecomte spent 5.8 hours swimming every day and then another hours sleeping; therefore, he spent more time in a horizontal (水平的) position than upright. This reduced the force of gravity acting on his body.

Fortunately, while the heart did shrink in size for Belly and Lecomte, it was just as strong and continued to function normally for both men. And in both cases, the heart regained its original mass and size after a return to normal daily lives,

This study is crucial as NASA prepares to send astronauts to Mars in the 2030s. Professor Levine is working with NASA on a program called cypher, which hopes to collect more in-formation by following ten more astronauts’ year-long trips as well as conducting research on shorter trips to space.

【推荐2】In 2007 a team led by Stefan Rahmstorf compared actual observations with predictions made by theoretical models for three key climate indicators: carbon dioxide, global temperature and sea-level rise. While the predictions got CO₂ levels right, they were low for real temperature and sea-level rise.

Climate scientists have a surprising habit: They often underestimate the climate threat. The articles reporting the underestimates have been widely cited, so one might think that scientists have taken corrective steps. But recent studies of Arctic warming suggest that the problem may not have gone away. As polar ice melts because of global warming, the Arctic Ocean absorbs more heat, which causes the Arctic to warm even more. It should surprise no one that the area is warming fast. Yet scientists have been caught off-guard by just how fast the region is heating up.

In 2013, a paper was published pointing out that these underestimates represent subconscious bias (偏向) caused by defensiveness. Scientists tended toward lower and misleading prediction because they did not want to be accused of making dramatic and overstressed claims. Even now scientists continue to be accused of overestimating climate risks by worrying figures which get much media attention, thus biasing their models to be unrealistically conservative.

If scientists have underestimated Arctic warming, they have likely minimized amounts of permafrost (永久冻土) melting and methane (甲烷) release as well. And that could be truly dire because the permafrost holds about 1.5 billion tons of organic carbon, twice as much as now in the atmosphere. Were that carbon to be rapidly released, it could cause a picture: a runaway greenhouse effect. Whatever the cause, it’s time that scientists looked seriously at whether their measuring models continue to underestimate critical aspects of the climate problem. Low estimates can create the false impression that we have more time to fix the problem than we actually do.

【推荐3】Women in post-pregnancy tend to respond slower to the outside world than they did before. In the West, this phenomenon is called “pregnancy brain”. In China, people describe it as “women are slower and less sharp for three years after giving birth.” However, studies showed that they are not less sharp. Rather, their brains are becoming better wired for parenting at the cost of memory.

In their 2016 research, Elseline Hoekzema and her team from the Netherlands scanned 25 women’s brains before and during pregnancy. The MRI results showed that there was a decrease in the amount of expectant mothers’ grey matter in their brains, which is responsible for multiple functions, including muscle control, emotions, speech and memory.

The decrease in grey matter isn’t necessarily a bad thing. Hoekzema compared it with the drop in the grey matter of teenagers during puberty (青春期). According to a previous study, during puberty, teenagers’ hormones cause a reduction in unnecessary synapses (突触), the connections between nerve cells. This process makes the brain work more efficiently. Likewise, the reduction of grey matter in new mothers’ brains might lead to greater parenting abilities.

The changes in the region of grey matter affected by pregnancy are known to play a role in social cognition (认知). This change might help a new mother better understand and decode her baby’s facial expressions and needs. Based on the results, scientists believed that the female brain experiences changes to help them better prepare for motherhood.

In a recent study led by Jonny Kohl from London’s Francis Crick Institute, experiments on the brains of pregnant mice provide concrete evidence that specific hormones improved connections between neurons (神经元) associated with parenting behaviors. While conducted on mice, this brain remodeling agrees with previous human studies, suggesting shared mechanisms, Newsweek reported.

However, this improvement in parenting-related skills might come at a cost. A 2010 study showed pregnant women have poorer memory skills than non-pregnant women, particularly concerning spatial recognition memory. This explains why many pregnant women sometimes lose their way on familiar routes.

And according to Hoekzema, the changes in women’s brains are long-lasting. So, next time your mom gets lost in a familiar place, be patient and kind to her. After all, her brain changed to bring you into the world!