Why Your Brain Actually Works Better in Winter
作者：Christian Jarrett @ 2016-2-14
来源：science of us，http://nymag.com/scienceofus/2016/02/debunking-the-myth-of-the-winter-blues.html#.
It was terrifyingly cold in New York this weekend, and this cold snap occurred right as we’re entering the postholiday doldrums. It’s around the time of the year when people start to talk about seasonal changes to their mood and energy level — most commonly, seasonal affective disorder, or SAD. While SAD is a relatively new condition — it stems from research in the ‘80s — it has become a huge part of how we in the colder climes discuss winter.
Everyone knows how winter affects certain people: It lowers their mood, makes them more prone to depression, and, in some cases, slows their mind to a crawl. There’s a reason for the popular image of someone wanting to just curl up in bed to wait out the duration of a frigid February afternoon.
But scientists are coming to realize that this might not be quite right. A pair of new studies challenge many of the popular assumptions about the psychological effects of wintertime, suggesting that we should look at the season in a new, brighter light. The weather might be gray and chilly, but the latest science says we humans are better at dealing with this than we usually give ourselves credit for, both in terms of our mood and the basic functioning of our brains.
The first study is a massive investigation published recently in Clinical Psychological Science involving 34,294 U.S. adults. It casts doubt on the very notion that depression symptoms are worse in the winter months.
The researchers, led by Professor Steven LoBello at Auburn University at Montgomery, asked their participants to complete a questionnaire about their depression symptoms over the previous two weeks. Crucially, the participants all completed the survey at different times of the year, allowing the researchers to look for any seasonal patterns.
Contrary to what you might think, the results provided no evidence whatsoever that people’s depression symptoms tended to be higher in winter — or at any other time of the year. This lack of a seasonal effect was true whether looking at the entire sample or only respondents with depressive symptoms. The respondents’ geographical latitude and sunlight exposure on the day of the survey were also unrelated to depression scores.
The researchers are clear about what this means for what they call the “well-entrenched folk theory” that winter brings on or worsens depression. Their results, they write, “cast serious doubt on major depression with seasonal variation as a legitimate psychiatric disorder.”
They think the early studies on the concept of SAD were flawed by virtue of the fact that they selectively recruited people who said they suffered from winter-related mood changes — an approach that was likely susceptible to confirmation bias, or selectively interpreting evidence to support a theory you already have.
This makes intuitive sense. Once the concept of SAD was introduced, after all, it captured the public imagination and went on to spawn a whole industry based around ways to treat the “condition,” including using artificial light.
In spite of the sketchy evidence for SAD, once it was accepted that the dark months affect our mood, it was only a small step to assuming that they probably have an adverse effect on our cognition, too — hence the internet now being full of articles on how to beat that winter sluggishness.
But this idea, too, is challenged by a new piece of research. That paper, published in Proceedings of the National Academy of Sciences, looked at whether the time of year affects basic brain function. It’s one of the first studies to do so, and, like the depression-scores study, it seems to refute a common cultural understanding of the effects of cold, dark days.
The neuroscientists, led by Christelle Meyer at the University of Liège in Belgium, recruited 28 young men and women at different times of year to answer questions about their mood, emotions, and alertness; have their melatonin (a hormone that regulates the sleep cycle) levels measured; and complete two psychology tasks in a brain scanner.
One task was a test of vigilance and involved pressing a button as fast as possible whenever a stopwatch appeared at random intervals on-screen, and the other was a test of working memory, which involved listening to streams of letters and spotting when the current letter was the same as the one presented three items earlier. The basic idea was to see if the participants’ brain activity during these tasks was different depending on the season.
The participants’ feelings of alertness, their emotional state, and melatonin levels mostly didn’t vary with the seasons, and they actually performed equally well on both tasks in the scanner regardless of the time of year, thus undermining the idea that the winter has an adverse effect on our mental abilities (more on this shortly).
One question on mood did show some seasonal variation, but participants’ moods were lowest in the fall, not winter. In terms of underlying brain function, participants’ neural activity was highest during the memory task for those participants tested in spring and lowest for those tested in the fall, so, far from being a special case, winter brain activity sat in the middle.
Meanwhile, during the vigilance task, brain activity was lowest in the winter and highest in the summer. Some media outlets have interpreted this as evidence for winter sluggishness, but as the participants’ performance and alertness was as good in winter as at other times of year, their reduced winter brain activity can actually be seen as a sign of improved efficiency. For comparison, consider research showing how the more expert people become at a task, the less brain activity is seen while they perform that task, as the brain becomes more efficient.
You could even think of this reduced winter neural activity as your brain entering a kind of “eco mode,” allowing it to perform as well as it does in summer but while consuming fewer resources. This makes sense from an evolutionary perspective: When resources are scarce and the weather is harsh, it’s obviously advantageous that the brain should be capable of performing basic tasks, especially those involving vigilance, in an economic fashion. (I should note that this is my interpretation — the researchers remain relatively neutral about the meaning of the seasonal effects they observed, and didn’t return an email I sent them inquiring about what those effects might mean.)
This suggestion that our mental function might actually be enhanced in winter is actually backed up by a (frequently ignored) study published in the late 1990s in Applied Cognitive Psychology. Researchers at the University of Tromsø in Norway tested 62 participants on a range of mental tasks in winter and again in summer (some completed them in winter first, the others in summer, thus balancing out any practice effects).
This was just about the perfect setting for such a study, since the contrasts were so extreme: Tromsø is located more than 180 miles north of the Arctic Circle, meaning there is virtually no sunlight in Tromsø during the winter and no darkness in the summer.
Across the battery of tests, the researchers found little evidence of seasonal effects, but those they did find were largely in favor of a winter advantage. In winter, participants performed better on two different tests of reaction time, and they showed evidence of enhanced mental control on the well-established Stroop test that involves naming color words while ignoring the ink color they are written in. Only one test showed a slight summer advantage, and that was for verbal fluency.
Summing up their findings, Dr. Tim Brennan and his colleagues wrote that “despite the subjective feeling one may have that one is mentally sluggish in winter, our data do not lend empirical support to the intuitive claim.”
Many people dislike winter for obvious reasons, and the idea that these darker months make many of us profoundly miserable and cognitively impaired fits a narrative about this being a difficult time of year (as Adam Gopnik wrote, “one of the most natural metaphors we make is of winter as a time of abandonment and retreat. The oldest metaphors for winter are all metaphors of loss”).
But we should be cognizant of how our expectations shape the way we experience the world — it may be the case that, after hearing over and over and over that winter slows us down, making us more sluggish and sad, we interpret days when we’re feeling down for other reasons as proof that it’s winter’s fault.
Sure, the winter presents us with many practical challenges, like coping with colds and flu and getting to work through the snow, but what these new studies suggest is that the season doesn’t have some mystical, malevolent effect on our brains. If anything, the data suggest that our minds are more sprightly at this time of year than in the summer. Now there’s some news to brighten your day — even if it’s an abysmally cold, short one.