When we encounter a stressful or frightening situation, our heart rate increases, our breath quickens, and our muscles become tense. 【小题1】 In fact, for most of history, we have assumed that there is a line separating our natural response and our learned behavior. But recent brain research has proved that our brain can change in structure and function throughout our life, depending on our experiences. So would it be possible to train our brain to control our “natural responses,” such as to fear?

One of the most surprising ways to control our fear response is breathing. Combat trainers, for example, use “tactical (战术性) breathing” techniques to prepare FBI agents for crisis situations. 【小题2】 One version that police officers learn works like this: Breathe in for four counts; hold for four counts; breathe out for four counts; hold for four; start again. How could something so simple be so powerful?

The breath is one of the few actions that lie in both our somatic nervous system (which we can consciously control) and our autonomic system (which includes our heartbeat and other actions we cannot easily access). 【小题3】 By consciously slowing down the breath, we can slow down the natural fear response that otherwise takes over.

【小题4】 Sara Lazar, an instructor at Harvard Medical School, compared the brain images of meditators (冥想者) with those of nonmeditating people. She found the meditators had 5 percent thicker brain tissue in the parts of the brain that are used during meditation — that is, the parts that handle emotion regulation, attention, and working memory, all of which help control stress.

Such studies suggest that meditators — like deep-breathing police officers — may have found a way for us to evolve past the basic human fear response. 【小题5】

It is widely accepted that being overweight definitely poses a danger to our health. According to a new study, obesity may even damage the brain’s ability to recognize the sensation of fullness and be satisfied after eating fats and sugars.

Further, those brain changes may last even after people considered medically obese lose a significant amount of weight — possibly explaining why many people often regain the pounds they lose.

The study, published Monday in Nature Metabolism, was a controlled clinical trial in which 30 people considered to be medically obese and 30 people of normal weight were fed sugar carbohydrates (glucose), fats (lipids) or water (as a control). Each group of nutrients was fed directly into the stomach via a feeding tube on separate days.

The night before the testing, all 60 study participants had the same meal for dinner at home and did not eat again until the feeding tube was in place the next morning. As either sugars or fats entered the stomach via the tube, researchers used functional magnetic resonance(磁共振) imaging and single-photon emission computed tomography(断层扫描技术) to capture the brain’s response over 30 minutes.

In people with normal weight, the study found brain signals in the striatum(纹状体) slowed when either sugars or fats were put into the digestive system — evidence that the brain recognized the body had been fed. At the same time, levels of dopamine rose in those at normal weight, signaling that the reward centers of the brain were also activated. However, when the same nutrients were given via feeding tube to people considered medically obese, brain activity did not slow, and dopamine levels did not rise.

Next, the study asked people with obesity to lose 10% of their body weight within three months — an amount of weight known to improve blood sugars, reset metabolism and boost overall health.

Tests were repeated as before — with surprising results. Losing weight did not reset the brain in people with obesity.

Much more research is needed to fully understand what obesity does to the brain, and if that is triggered by the fat tissue itself, the types of food eaten, or other environmental and genetic factors.

If you're one of the millions of those who use escalators each year, you are probably deeply familiar with the vertical grooves（竖凹槽）that cover each stair. Few of us have stopped to consider why they exist, though. In fact, it's one of the everyday things we take for granted.

But it is a little complicating when you think about it. Sure, the deep, grey lines make an escalator's metal stairs more appealing to the eye. But regular stairs don't have grooves like these; why do escalators need them? Is it because of the movement?

It turns out those grooves serve a more functional purpose. And, yes, it does have to do with the movement, as well as with general cleanliness! Anyone who has ridden an escalator knows that the steps everlastingly circulate from the top to the bottom. You've surely noticed the ridged yellow lip at the top of the escalator. But here's what you may not have noticed: As an escalator's steps flatten, this ridge—also called the comb plate—sweeps away any trash or litter that might have fallen on the stairs. Those grooves lock the step and comb plate together, which makes it harder for any dangerous materials to slide underneath the lip. This prevents foreign objects from getting stuck in that gap, potentially causing the escalator to stop, or worse, break down completely.

That's not the only reason why the grooves were created, though. They are also a good place for water to pool together, protecting you from a bad fall on the slick surface.

So the next time you step on an escalator, take a moment to appreciate those metal grooves. They exist to make sure you get to your office meeting on time.