According to new study, people, who suffer from anhedonia, a key symptom of depression, are less likely to pursue rewards if there is any need to put an effort to obtain them.
The research has indicated that decreased cravings for pleasure may be at the root of a core symptom of major depressive disorder.
The research, led by Vanderbilt psychologists Michael Treadway and David Zald, is contrary to 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," said Treadway.
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.
But, researchers have always found it difficult to understand the different components of anhedonia, the desire to obtain something pleasurable versus experiencing pleasure-in humans.
"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. 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," said Treadway.
For the study, the researchers 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, one hard, one difficult, to obtain monetary rewards.
Participants were eligible but not guaranteed to receive money each time they completed a task successfully.
The subjects were told at the beginning of each trial whether they had a high, medium or low probability of winning a prize if they successfully completed the trial.
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.
"Consistent with our hypotheses, we found that individuals with self-reported anhedonia made fewer hard-task choices. These findings are consistent with theoretical models linking anhedonia to decreased (dopamine levels)," wrote the authors.
Treadway said: "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."
The research was recently published by the online journal PLoS One.