Seasonal Affective Disorder: Longer Days or Nights Can Change Your Behavior

Seasonal affective disorder (SAD) is known as a type of depression that occurs and disappears in a seasonal pattern, characterized by feeling sad or down in relation to seasonal changes.

It is also called "winter depression." This is because SAD symptoms transpires when days are short and nights are longer during winter.

Bright light therapy has been proven as an effective treatment for SAD, as well as non-season-related depression, postpartum depression, and bipolar depression. However, the specific impact of seasonal changes in terms of day length and light exposure to the brain, at least in cellular level, remains a mystery for the scientific community.

Now, a new study led by researchers from the United States discovered the neurological mechanism behind this mysterious mental health condition. The research team explored the repercussions of SAD to the so-called suprachiasmatic nucleus or SCN, a small structure inside the hypothalamus of the human brain.

The team also found SAD alters the neurons in the paraventricular nucleus or PVN, a region of the brain which is responsible for various bodily function like controlling metabolism, stress, growth, reproduction, immune system, and other autonomic functions. These functions are generally non-voluntary, meaning biological processes operate whether intended or not by a living organism.

Seasonal Affective Disorder

(Photo : Photo by CHANDAN KHANNA/AFP via Getty Images)

In the new paper published in the journal Science Advances on Friday, September 2, confirm seasonal changes in day length or photoperiod affect multiple physiological functions. The breakthrough study also supports the long-held notion that longer days or nights during summer and winter seasons also has an impact to humans.

Conventional terminologies have led to terms like "gloomy weather" or "cold nights," which are linked to emotions or feelings connected with seasonal depression.

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SCN-PVN Network

The most significant novel finding that the new research provided is the discovery that SCN-PVN network can be artificially manipulated. In particular, changing the activity of some SCN neurons and successfully increasing dopamine expression in the hypothalamic PVN network, according to David Dulcis, an associated professor from UC San Diego, as cited by News Medical.

In particular, the UC San Diego researchers used a mouse model to show a reflect a process which affect neurons and neurotransmitters in response to the day length, which trigger the said behavioral changes. Since mice brains function almost similarly to humans, the researchers said the altered SCN neurons also affect brain activity and subsequent daily behaviors.

Novel mechanism

Authors of the study reportedly consider their findings provide a novel mechanism on explaining how the brain adapts to seasonal changes during light exposure. For now, early identification and diagnosis of SAD is key medical best practice that medical professionals can undertake.

According to the UK-based National Health Service (NHS), SAD can be challenging to diagnose since there are other types of depression that resembles it.

Yet, the NHS says a SAD diagnosis can be typically confirmed when one's depression occurs at the same time or period each year for at least two years. In addition, the mentioned periods of depression are followed by periods without depression.