Over hundreds of thousands of years, the human brain has evolved to respond to light changes.

For instance, darkness at night triggers our bodies to rest. This may be a result of the fact that our ancient ancestors would have confronted greater risks from predators if they attempted to hunt for food at night.

Interestingly, new research suggests that bright-light exposure influences brain activity when research volunteers carry out a risk-taking task.

Danish neuroscientists performed functional MRI scans on volunteers both before and after bright-light therapy to determine whether light altered the subjects’ risk-taking and brain activity while gambling.

The bright-light exposure clearly increased risk-taking among the subjects — and did so in proportion to the amount of treatment.

These responses corresponded to activity in the brain’s striatum, a region that controls current and anticipated rewards.

This may be the reason why casinos remain brightly lit 24 hours a day, in order to keep players at the tables taking risks.

People who suffer from seasonal affective disorder have problems with certain neurotransmitters — which are brain messengers that control mood.

One study showed that patients with seasonal affective disorder (SAD) had increased levels of a serotonin transporter protein called SERT during the winter months.

During the summer months, the greater amount of sunlight helps lower SERT levels. But with longer hours of darkness during the fall and winter, SERT levels increase, which lowers serotonin activity.

Seasonal affective disorder patients may also have too much of the hormone melatonin, which is produced as a response to darkness and makes people feel sleepy.

In fact, a melatonin supplement helps many people who suffer with insomnia.

For people with SAD, longer winter days and the corresponding boost in melatonin contribute to daytime sleepiness and lethargy.

Less skin exposure to light also lowers the amount of vitamin D a person produces. Deficiency of this vitamin has been associated with depression.

These chemical changes in the body and the brain affect circadian rhythms.

Patients with SAD have difficulties adjusting their internal clock in response to the seasonal change in the length of the day.