No desire for pleasure? Could mean you are depressed.
By Catherine Walker
A decreased desire for pleasure may be a key predisposing factor for major depression a new study suggests.
The long-held idea that those suffering from depression lack the ability to enjoy rewards, rather than the desire to seek them is challenged by this research.
The study, which is published by the online journal PLoS One, was conducted by Vanderbilt psychologists Michael Treadway and David Zald.
‘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,’ Treadway, a graduate student in psychology, said.
Decreased motivation to seek and experience pleasurable experiences is a primary symptom of major depressive disorder. This is known as anhedonia.
Anhedonia often persists after other symptoms of depression abate and is less responsive to many antidepressants.
To understand the different components of anhedonia in humans has been difficult for researchers. ‘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 said.
‘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 added.
To explore the role of reduced desire and motivation in individuals reporting symptoms of anhedonia, Treadway and his colleagues devised the Effort-Expenditure for Rewards Task (EEfRT).
EEfRT involved having individuals play a video game that gave them the opportunity to choose between two different tasks. One hard task and one difficult task were designed to obtain monetary rewards. The participants were eligible to receive money each time they completed a task successfully although this reward was not guaranteed.
In ‘the hard task’ the participants were required to press a button 100 times in 21 seconds using their ‘non-dominant’ little finger and carried a potentially higher reward than the easy task. The easy task required the pressing of a button 30 times in seven seconds using the ‘dominant’ index finger.
The participants were informed at the beginning of each trial whether they had a high, medium or low probability of winning a reward if they successfully completed the trial. The subjects could choose which trials they completed and were offered 20 minutes to carry out as many tasks as they could.
The researchers found that the participants who had symptoms consistent ith anhedonia were less likely to choose the tasks which required greater effort in exchange for greater reward, particularly if the rewards were uncertain.
‘Consistent with our hypotheses, we found that individuals with self-reported anhedonia made fewer hard-task choices,’ the authors reported. ‘These findings are consistent with theoretical models linking anhedonia to decreased (dopamine levels).
‘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 concluded.
Source: Vanderbilt University
