joining us live now to talk about it, stanford assistant professor in psychiatry jason tucciarone. doctor tucciarone, thanks for your time. >> kristen, thanks for having me. so what is seasonal depression and how common is it? seasonal depression is very common. uh- happens almost 5% of patients that we see even up to 10% in primary care facilities. primary care clinics. and it's really a depression that's kind of coupled to uh- the late fall and early winter. and namely reductions in sunlight and exposure to sunlight. >> can you explain why that reduction in sunlight, what does it do to us physiologically, you know, why does it lead to those feelings of depression? >> sure. the mechanisms aren't totally understood, but we do think that, uh, disruptions in light can mess with certain aspects of our brain, referred to as our circadian rhythms. and our circadian rhythms are regulated by a region of our brain called the hypothalamus. but uh, this region of the hypothalamus called the suprachiasmatic nucleus, regulates multiple processes in our body, including our sleep, our metabolism