A workday filled with mentally challenging tasks can make people feel worn out and desire a relaxing evening of TV shows. A study led by Antonius Wiehler of Pitié-Salpêtrìère University Hospital provides an explanation for this familiar phenomenon.

Researchers arranged for two sets of subjects to work for over six hours. The first group was assigned a difficult version of tasks, while the second was given a simple version. They measured levels of glutamate (谷氨酸) that collected in the cognitive area of subjects’ brains, finding higher levels of the chemical appeared in the first group, although both groups reported feeling similar levels of tiredness after the daylong experiment. Glutamate helps learning and memory, but too much glutamate can give rise to brain cell damage.

Also, when researchers offered financial choices, as a measure of whether the difficulty of work affected subjects’ decision-making ability, those finishing harder tasks were more likely to choose to take home an immediate reward rather than wait for a larger cash-out at a later date. “Existing theories suggested fatigue (疲劳) is an unreal feeling cooked up by the brain to make us relax,” Wiehler says. “Yet our findings provide proof that cognitive work causes the collection of bad substances, so fatigue would be signal that makes us stop working but for a different purpose: to preserve normality of brain functioning.”

“Defining what fatigue is remains a challenge for the field, says neuroscientist Matthew Apps, “but it’s exciting that this experiment provides a reasonable alternative explanation that is of great help.” He notes some areas where these findings might come in. For people in jobs requiring intense focus, burnout can lead to damaging consequences. Preventing glutamate’ building may help maintain attention. Another area of interest would be researching clinical conditions related to fatigue. The presence of glutamate might reveal why patients struggle with fatigue.

For Wiehler, open questions remain. One limitation is their focus on the brain’s specific region, so what impact cognitively effortful work has on the rest parts remains to be seen. In addition, it’s not yet clear how the balance of glutamate is restored after rest. “Maybe it leaves the brain during sleep,” Wiehler says. “There’s tons of research to come.”

Why is pink or purple a color for girls and blue or brown for boys?

The answer depends largely on cultural values as well as personal experiences. To the Egyptians, green is a color that represents the hope and joy of spring, while for Muslims, it means heaven. Red is a symbol of good luck in many cultures. In China, children are given money in a red envelope to bring good fortune in the New Year. For many nations, blue is a symbol of protection and religious beliefs. Greek people often wear a blue necklace hoping to protect themselves against evils.

People's choice of colors is also influenced by their bodies' reactions(反应)toward them. Green is said to be the most restful color. It has the ability to reduce pain and relax people both mentally and physically. People who work in green environment have been found to have fewer stomachaches.

Red can cause a person's blood pressure to rise and increase people’s appetites(食欲). Many decorators will include different shades of red in the restaurant. Similarly, many commercial websites will have a red“Buy Now” button because red is a color that easily catches a person's eye.

Blue is another calming color. Unlike red, blue can cause people to lose appetite. So if you want to eat less, some people suggest that eating from blue plates can help.

The next time you are deciding on what to wear or what color to decorate your room, think about the color carefully.

People have wondered for a long time how their personalities and behaviors are formed. It’s not easy to explain why one person is intelligent and another is not, or why one is cooperative and another is competitive.

Social scientists are, of course, extremely interested in these types of questions. They want to explain why we possess certain characteristics and exhibit certain behaviors. There are no clear answers yet, but two distinct schools of thought on the matter have developed. As one might expect the two approaches are very different from one another, and there is a great deal of debate between proponents of each theory. The controversy is often (conveniently) referred to as “nature/nurture”.

Those who support the “nature” side of the conflict believe that our personalities and behavior patterns are largely determined by biological and genetic factors. That our environment has little, if anything, to do with our abilities, characteristics, and behavior is central to this theory. Taken to an extreme, this theory maintains that our behavior is predetermined to such a great degree that we are almost completely governed by our Instincts.

Proponents of the “nurture” theory, or, as they are often called behaviorists, claim that our environment is more important than our biologically based instincts in determining how we will act. Behaviorists see humans as being whose behavior is almost completely shaped by their surroundings. Their view of the human being is quite mechanistic; they maintain that like machines, humans respond to environmental stimuli as the basis of their behavior.

The social and political implications of these two theories are profound. In the United States, for example, blacks often score below whites on standardized intelligence test. This leads some “nature” proponents to conclude that blacks are genetically inferior to whites. Behaviorists, in contrast, say that the differences in scores are due to the fact that blacks are often deprived of many of the educational and other environmental advantages that white enjoy, and that, as a result, they do not develop the same responses that whites do.

Neither of these theories can yet fully explain human behavior. In fact, it is quite likely that the key to our behavior lies somewhere between these two extremes. That the controversy will continue for a long time is certain.