One key characteristic of clinical depression is anhedonia, the complete lack of pleasure in things and activities that used to be rewarding. A new study in rats has now uncovered an important biological factor that contributes to this state.

The World Health Organization (WHO) state that across the world, more than 300 million people of all ages live with depression. Moreover, the WHO add, this condition is also “the leading cause of disability worldwide.”

In the United States, more than 16.1 million adults have received an official diagnosis of major depressive disorder, according to the Anxiety and Depression Association of America.

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