How the seasons affect your sleep 季节如何影响你的睡眠

　　季节会影响我们的睡眠吗？根据最新研究，答案是肯定的。本期节目介绍我们的睡眠模式是如何演变而成的，以及光和温度是否会对睡眠时间产生影响。

　　词汇：sleep 睡眠

　　After a long winter, the arrival of spring can be a welcome relief. The days grow longer, the temperatures increase, and the natural world around us comes to life again. But when the seasons change, our sleep patterns change with them.

　　New research suggests that humans may need more sleep in the winter than they do in the summer. A German study found that participants slept an hour longer in December than in June, regardless of their exposure to light. "Our study shows that even while living in an urban environment, with just artificial light, humans [experience] seasonal sleep," says Dieter Kunz, one of the study's lead authors and head of the clinic of sleep and chronomedicine at St Hedwig Hospital in Berlin, Germany. The study found that the participants experienced seasonal variations in their rapid eye movement sleep, also known as REM sleep, as well as in their slow wave sleep, also known as deep sleep. REM sleep, which is when we dream and our heart rate increases, was 30 minutes longer in the winter than during the summer. Slow wave sleep, which is when our muscles are repaired, our immune system is strengthened and our memory is consolidated, was 30 minutes shorter in September than in February.

　　But why do our bodies and brains need more rest at certain times of year? The answer could lie in our evolutionary past. That's according to Neil Stanley, who's a sleep expert at Sleep Station, an online provider of cognitive behavioural therapy for insomnia. "We have evolved to dark-light cycles, so when we wake up on a winter's morning and it's dark, our brain is going 'I can't do anything… there's no point leaping out of bed.'" Particularly in summer, temperature also plays a role – our bodies require a skin temperature of between 31-35 degrees centigrade [Celsius] for a good night's sleep, but this can be harder to control during the warmer months.

　　Of course, nowadays, it is our school and work times – not the Sun – that determine when we get up in the morning. But, as autumn approaches, it seems we now have a good excuse for an early night.

　　词汇表

　　relief （不快后的）解脱

　　come to life 复苏，恢复生机

　　sleep pattern 睡眠模式

　　exposure to 接触

　　artificial light 人造光

　　seasonal sleep 季节性睡眠

　　chronomedicine 时间医学

　　variation 变化

　　rapid eye movement sleep 快速眼动睡眠

　　slow wave sleep 慢波睡眠

　　deep sleep 深度睡眠

　　repair 修复

　　immune system 免疫系统

　　consolidate 加强，加固

　　rest 休息

　　cognitive behavioural therapy 认知行为疗法insomnia 失眠

　　evolve 逐渐进化

　　dark-light cycle （昼夜）光暗循环

　　leap out of bed 跳下床，起床

　　early night 早睡