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          2019-02-15 来源:国外网站推荐 - 由[国外网站大全]整理 30

            You're not alone if colder weather and longer nights make you feel down.


            This well-known phenomenon,called seasonal affective disorder(SAD),might explain why people feel low,irritable,and lethargic in the winter months.For some,the condition can be serious and debilitating.



            Although SAD is a recognised form of clinical depression,experts are still divided on what causes the condition,with some even arguing it doesn't exist.But my own research has found that your eye colour might actually be one factor determining whether or not you develop SAD.


            We have uncovered evidence that a person's eye colour can have a direct effect on how susceptible they are to SAD.


            Our study used a sample of 175 students from two universities(one in south Wales,the other in Cyprus).We found that people with light or blue eyes scored significantly lower on the seasonal pattern assessment questionnaire than those with dark or brown eyes.


            These results agree with previous research which found that brown or dark-eyed people were significantly more depressed than those with blue eyes.


            The reason that eye colour may make some people more susceptible to depression or mood changes might be because of the amount of light an individual's eyes can process.


            The retina is the part of our eyeball containing cells that are sensitive to light.When light enters the eye,these cells trigger nerve impulses that form a visual image in our brain.


            In 1995,scientists discovered that some retinal cells,rather than forming an image,simply send information about levels of brightness from the back of the eye to the brain's hypothalamus.


            The hypothalamus is an important part of the brain which secretes hormones(such as oxytocin)that regulate temperature,hunger and sleep cycles.


            As the amount of blue and green light reaching the hypothalamus increases,the amount of melatonin decreases.Eyes with lower pigment(blue or grey eyes)are more sensitive to light.


            This means they don't need to absorb as much light as brown or dark eyes before this information reaches the retinal cells.


            As such,people with lighter eyes release less melatonin during the fall and winter.This mechanism might provide light-eyed people with some resilience to seasonal affective disorder(though a smaller proportion may still experience SAD).