As the name suggests, serotonin transporter removes serotonin from the brain. Serotonin itself is what regulates physical and emotional functions like eating, energy levels, and mood. During the winter, subjects had higher levels of serotonin transporter in the brain than they did during the summer. When tested, not just one but all investigated areas of the brain followed this same trend. All subjects were healthy human beings, so whether you are a marathoner or a couch potato, you can expect your serotonin to hibernate for the winter, at least to some degree. Professional ice fishermen may disagree, and further tests may need to be conducted on Minnesotans, who live in one of the coldest climates in North America, yet manage to stay so darn nice.