Ten years ago, researchers discovered a small group of people who derive no pleasure from music despite having normal hearing and the ability to enjoy other experiences or stimuli. The condition, "specific musical anhedonia," is caused by a disconnect between the brain's auditory and reward networks. In a paper publishing August 7 in the Cell Press journal Trends in Cognitive Sciences, the team that discovered specific musical anhedonia describes the brain mechanisms behind the condition and discusses how understanding it could reveal other differences in how people experience pleasure and joy.
"A similar mechanism could underlie individual differences in responses to other rewarding stimuli," says author and neuroscientist Josep Marco-Pallarés of the University of Barcelona. "Investigating these circuits could pave the way for new research on individual differences and reward-related disorders such as anhedonia, addiction, or eating disorders."
To identify musical anhedonia, the team developed a tool called the Barcelona Music Reward Questionnaire (BMRQ ) that measures how rewarding a person finds music. The questionnaire examines five different ways in which music can be rewarding: by evoking emotion; by helping regulate mood; by fostering social connections; through dance or movement; and as something novel to seek, collect, or experience. People with musical anhedonia generally score low on all five aspects of the BMRQ.
Behavioral and brain imaging studies have both supported the idea that specific musical anhedonia is due to a disconnection between brain regions. People with the condition can perceive and process musical melodies, meaning that their auditory brain circuits are intact—they simply don't derive pleasure from doing so. Similarly, fMRI scans show that when listening to music, people with musical anhedonia have reduced activity in the reward circuit—the part of the brain that processes rewards including food, sex, and art—but a normal level of activity in response to other rewarding stimuli, such as winning money, indicating that their reward circuit is also intact.
"This lack of pleasure for music is explained by disconnectivity between the reward circuit and the auditory network—not by the functioning of their reward circuit, per se," says Marco-Pallarés.
"If the reward circuit is not working well, you get less pleasure from all kinds of rewards," says author and neuroscientist Ernest Mas-Herrero of the University of Barcelona. "Here, what we point out is that it might be not only the engagement of this circuitry that is important but also how it interacts with other brain regions that are relevant for the processing of each reward type."
Why people develop the condition is still unclear, but studies have shown that genetics and environment could both play a role. A recently published study in twins shows that genetic effects could be responsible for up to 54% of how much an individual enjoys music.
Even among healthy people, there is a lot of variation in how responsive people are to rewards, but research into specific reward types is relatively rare given that most research into the reward circuit has assumed that reward responsiveness is an all-or-nothing phenomenon—which is not the case.
"We propose that using our methodology to study other reward types could yield the discovery of other specific anhedonias," says Marco-Pallarés. "It's possible, for instance, that people with specific food anhedonia may have some deficit in the connectivity between brain regions involved in food processing and the reward circuitry."
The team is currently collaborating with geneticists to identify specific genes that might be involved in specific musical anhedonia. They also plan to investigate whether the condition is a stable trait or something that changes throughout life—and whether musical anhedonia or other similar conditions can be reversed.
