Science Sub-Journal: How Changes in Daytime Length Change the Brain and Subsequent Behavior

Seasonal variations in light — summer day lengths, winter days shorter — have long been linked to human behavior, affecting everything

Bright light therapy has been shown to be effective for treating SAD, as well as for diseases such as non-seasonal major depressive disorder, postpartum depression and bipolar disorder, but how seasonal variations in day length and light affect and alter the brain at the cellular and circuit levels has largely left scientists clueless

In a new study published Sept.

The work was led by senior study author Dr.

Hidden in the hypothalamus of the human brain is a small structure called the superior optic nucleus (SCN), each of which consists of about 20,000 neurons

The SCN is the body's timekeeper, regulating most of the circadian rhythms— changes in body, mind, and behavior follow a 24-hour cycle, affecting metabolism, body temperature, and the timing of hormone release

In the new study, Dulcis and colleagues describe how SCN neurons coordinate with each other to adapt to different lengths of daylight and change

Seasonal changes in light also indicate that the number of neurons expressing neurotransmitters in the paraventricular nucleus (PVN), a region of the brain that plays an important role

"The most impressive new finding in this study is that we discovered how to artificially manipulate the activity of specific SCN neurons and successfully induce dopamine expression in the PVN network of the hypothalamus," Dulcis said

Lead author Dr Alexandra Porcu, a member of Dulcis' lab, added: "We reveal new molecular adaptations

The authors believe that their findings provide a new mechanism that explains how the brain adapts to seasonal changes in