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University professors find brain circuit likely related to seasonal affective disorder

Connection found between light-sensitive cells of eye, regions of brain

In a Society for Neuroscience meeting last November, two University professors presented their discovery of a specific brain circuit that could be involved with mood disorders, including seasonal affective disorder and depression.

Jerome Sanes, professor of neuroscience and director of the University’s MRI Research Facility, and David Berson ’75, professor of ophthalmology and chair of the department of neuroscience, were the lead authors on a study responsible for identifying a connection between light-sensitive cells in the eye and regions in the brain that affect mood.

Sanes and Berson’s search for this particular circuit in human brains was inspired by recent work done at the National Institute of Mental Health, which found a very similar circuit in mouse brains. “The mice were subjected to 3.5 hours of light and 3.5 hours of dark,” said Sanes. This light pattern caused a behavior in mice analogous to human depression; when the researchers eliminated the light-sensitive eye cells involved in the hypothesized brain circuit, the depression-like symptoms went away. “That suggested that this brain pathway might have an importance for depression,” Sanes added.

Sanes and Berson sought to answer the question: “Is there a region (of the human brain) also activated by the same light stimulus that activates the pathway in mice?” Berson explained.  Although light-related depression in humans is a well-known phenomenon, not much is known about the specific mechanisms in the brain underlying the relationship between light and mood, Berson added.

To try to answer this question, Sanes and Berson utilized functional magnetic resonance imaging, which allows scientists to measure brain activity in different regions. The team wondered how changing light intensity would affect brain activity in a specific region, and they measured this activity using an fMRI, Berson said. These experiments revealed human brain activity in a highly complex region very similar to the region found in mice. “We don’t know if it’s exactly the same area as in the mouse or if it’s the same circuit,” but it supports the idea that the circuit could be present in all mammals, he added.

“Some of the brain areas which had the light-related sensitivity have been implicated in depression and (SAD),” Sanes said. Understanding the brain circuit involved in mood disorders like SAD is important for developing treatments for these conditions, said Samer Hattar, one of the lead authors on the mouse study and chief of the section on light and circadian rhythms at the NIMH. “This (research) is exciting because for the last six years, there haven’t been any good drugs or treatments for treating depression,” he added. Now, knowledge of the existence of this circuit will allow researchers to attempt manipulating its function to create beneficial mood disorder treatment, he added.

In addition to the possible link to SAD, this light-sensitive circuit could have implications in decision-making, Sanes and Berson mentioned.

Their research on this human brain circuit will be submitted for publication in about a month and a half, after which it will undergo review for about six months, said Sanes, adding that they hope this publication will lead to further research on mood disorders.


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