Young people with a diminished ability to feel pleasure often have a hard time adjusting their physical activity to obtain greater rewards. Recent experiments suggest that this disconnect arises from specific cognitive difficulties in learning about both the reward and the physical cost required to obtain it. A study detailing these results was recently published in the journal Psychological Medicine.
Depression is a leading cause of disability worldwide. The core feature of this condition is anhedonia. This symptom manifests as a general lack of interest and a blunted ability to like or desire things that most people find rewarding.
Psychologists often divide anhedonia into two different categories. Anticipatory anhedonia refers to a diminished ability to anticipate positive future events. Consumptive anhedonia refers to a decreased ability to enjoy positive events in the physical moment.
Both types of anhedonia affect how individuals navigate their daily environments. We always make decisions based on past experience, weighing the expected rewards against the required physical or emotional costs.
Reward learning involves tracking which actions provide the greatest benefit over time. Effortful learning involves understanding the energy costs associated with selected actions.
If we don’t know exactly which actions will lead to the best results, or if we have trouble estimating the energy required for those actions, we can miss out on positive experiences. Previous studies have shown that adults and adolescents with depression exhibit deficits in general reward learning.
Less is known about how depressed and anhedonic people learn about effort. Understanding the actual energy costs associated with a task is an essential part of daily decision-making.
Angad Sahni, a researcher at the University of Reading, led a team investigating this learning process in young people. The researchers wanted to see if anhedonia changes the way people find ways to maximize benefit and minimize effort.
They wondered if previous experiments had been too difficult for participants. Previous research designs required people to learn about reward and effort simultaneously.
These older settings required people to constantly switch their attention between assessing the value of the prize and assessing the physical strain of the task. The value of the prize was so high that participants were often distracted from thinking about the effort involved.
To eliminate this distraction, Sahni and his colleagues modified an existing computer-based learning task. They divided the experiment into different stages, allowing participants to focus on finding the reward in one stage and exerting effort in the other.
The experiment included 155 participants between the ages of 16 and 25. The volunteers experienced a wide range of symptoms of depression, from none at all to severe.
Before starting the computer task, participants completed a series of standardized questionnaires. These surveys assessed current levels of depression and anxiety, as well as specific experiences with both anticipatory and consummatory anhedonia.
The task itself is designed to assess behavioral learning through trial and error. The researchers selected photos of puppies to represent high rewards and photos of adult dogs to represent low rewards. Baby animals are consistently rated as very comfortable and provide immediate visual reward without the need for monetary reward.
Prior to the experiment, participants rated pictures of animals on a sliding scale from 0 to 100. Participants indicated how much they liked seeing puppies, how much they wanted to see them, and how much physical effort they were willing to expend for the opportunity to see puppies.
During the active learning block, youth were faced with a series of choices between two abstract shapes on a computer monitor. In the reward-focused block, selecting one shape produced a picture of a puppy 75 percent of the time and a picture of an adult dog 25 percent of the time. Another form gave the opposite odds.
Physical costs remained constant throughout the reward block. To display the image, participants had to quickly press 60 alternating keys on the keyboard to fill a blue bar on the screen.
In the effort-focused block, the reward was always a picture of an expensive puppy, but the physical cost varied. One shape often required a lot of effort, or 60 quick keystrokes. The other shape required only 35 keystrokes, which was relatively low effort.
Participants did not know the underlying odds when they began either phase. The instructions just ask you to figure out which shape will yield the most puppies and which shape will require the least input to fill the progress bar.
This setup allowed researchers to measure learning accuracy. They tracked how often participants succeeded in choosing the best shape in each block during a total of 50 trials. We also recorded the rate of alternating button presses as an objective measure of physical activity.
To gain deeper insight into the learning process, scientists applied computational models to behavioral data. These mathematical models help explain the hidden cognitive steps that drive decision-making.
One of the specific measurements they extracted was a temperature parameter. This metric captures the conceptual balance between behavioral exploration and exploitation.
Higher temperature values suggest that individuals are making more random and exploratory choices. A low temperature value indicates that the person is leveraging existing knowledge by consistently choosing options that are already known to be optimal.
Analyzing baseline ratings, the researchers found that higher levels of depression and completion anhedonia correlated with lower overall liking for puppy photos. Participants higher in anticipatory anhedonia reported lower willingness, preference, and subjective willingness to work for reward.
During the active task, participants generally pressed the alternating button faster for the high-reward pup than for the low-reward adult dog. This difference confirmed that the computer task was successful in measuring how people adjust their physical activity based on the intrinsic value of the prize.
Participants with more anticipatory anhedonia made fewer adjustments to their body speed. They expended the same amount of effort on puppies and adult dogs.
The data also revealed a link between symptom severity and learning accuracy. As general depressive symptoms increased, participants were no longer able to pinpoint which shapes yielded the highest reward.
High consummatory anhedonia was associated with a broader range of difficulties. Those who struggled to enjoy momentary rewards had decreased accuracy in both reward and effort blocks.
Results from a computational model provided a potential explanation for this poor performance. Higher consummatory anhedonia was correlated with increased temperature parameters during both phases of the experiment.
This suggests that these people chose their options more randomly. They continued to explore suboptimal shapes rather than exploiting shapes that reliably provided less effort and higher reward.
Over time, this pattern of underutilization of good opportunities means that anhedonic people receive fewer rewards in their daily lives and are likely to expend more energy than necessary. When unnecessary physical exertion is combined with small gains, the small amount of pleasure they can feel can be further reduced.
Although this discovery provides a clue to how motivation works, there are clear limitations to the current experiment. The researchers acknowledged that the participant pool lacked broad demographic diversity.
Most participants were female, Caucasian, and highly educated college students. Only a minority of volunteers had received a formal clinical diagnosis of depression from a medical professional.
The observed correlations were statistically modest, and some associations were not statistically significant after researchers adjusted the calculations for multiple test comparisons. The research team noted that the number of participants would need to be expanded to examine the subtle relationships between these symptoms and abstract learning parameters.
Future research should recruit more diverse participants, with a particular focus on patients diagnosed with clinical depression. Scientists also need to test how common psychiatric drugs affect patients’ ability to learn about rewards and physical costs.
Understanding the specific learning deficits associated with anhedonia may ultimately lead to new treatment strategies. By helping young people readjust their exploration habits and accurately estimate physical costs, clinicians may help them feel comfortable returning to rewarding experiences.
The study, “Anhedonia is associated with numeracy deficits in reward and effort learning in youth with symptoms of depression,” was authored by Angad Sahni, Anna-Lena Frey, and Ciara McCabe.
