VANDERBILT (US)—Decreased cravings for pleasure may be at the root of a core symptom of major depressive disorder. The new finding contrasts the long-held notion that those suffering from depression lack the ability to enjoy rewards, rather than the desire to seek them.
“This initial study shows that decreased reward processing, which is a core symptom of depression, is specifically related to a reduced willingness to work for a reward,” says Michael Treadway, a graduate student in psychology and part of the Vanderbilt University team that conducted the study.
Decreased motivation to seek and experience pleasurable experiences, known as anhedonia, is a primary symptom of major depressive disorder. Anhedonia is less responsive to many antidepressants and often persists after other symptoms of depression subside.
“In the last decade and a half, animal models have found that the neurotransmitter dopamine, long known to be involved in reward processing, is involved in craving or motivation, but not necessarily enjoyment,” Treadway says. “To date, research into reward processing in individuals with anhedonia has focused on enjoyment of rewards, rather than assessing the drive to work for them. We think this task is one of the first to do that.”
Treadway and his colleagues devised the Effort-Expenditure for Rewards Task, or EEfRT, to explore the role of reduced desire and motivation in individuals reporting symptoms of anhedonia. EEfRT involved having individuals play a simple video game that gave them a chance to choose between two different tasks to obtain monetary rewards. Participants were eligible but not guaranteed to receive money each time they completed a task successfully.
The researchers found that subjects who reported symptoms consistent with anhedonia where less willing to make choices requiring greater effort in exchange for greater reward, particularly when the rewards were uncertain.
“By addressing the motivational dimension of anhedonia, our findings suggest a plausible theoretical connection between dopamine deficiency and reward processing in depression, which may eventually help us better understand how anhedonia responds to treatment,” Treadway explains.
Funding from Vanderbilt University and the National Institute on Drug Abuse supported the research, which was published Aug. 12 by the online journal PLoS One.
Vanderbilt University news: www.vanderbilt.edu/news