Post by Flora Moujaes
What's the science?
Humans experience pleasure from abstract rewards, such as music, that do not confer any direct advantage for survival. Understanding how the brain translates music, a sequence of sounds, into a pleasant rewarding experience remains a challenge. Reward can be divided into three neurobiologically distinct components: hedonic pleasure (in-the-moment liking), motivation (or wanting), and learning. The role of dopamine in motivation and learning has been widely established in the animal literature, but dopamine’s function in hedonic pleasure is more controversial. Animal literature has tended to focus on primary rewards such as food and sex, rather than abstract rewards such as music. This week in PNAS, Ferreri and colleagues used a pharmacological intervention to explore for the first time whether dopamine function is causally related to the pleasure we experience from music, and how it influences both hedonic pleasure and motivation.
How did they do it?
Researchers manipulated dopamine transmission in 27 human participants while they listened to music in three different sessions, each at least a week apart. The authors began by orally administering either levodopa (a dopamine enhancer), risperidone (a dopamine blocker), or lactose (a placebo). Participants then listened to five of their favourite musical excerpts and 10 pop songs selected by the experimenters, which included a range of artists from Antonio Orozco to Taylor Swift. Pleasure responses were measured continuously 1) by participants indicating in real-time the degree of pleasure they were experiencing and 2) by measuring electrodermal activity: changes in the electrical properties of the skin that are related to emotional arousal. Motivational responses were measured using an auction paradigm, where participants indicated how much money they were willing to part with to buy the song. Finally, participants also completed a well-validated reward control task (the Monetary Incentive Delay Task) in order to verify that any changes caused by dopamine were related to the reward system, and not more general processes.
What did they find?
Researchers predicted that if dopamine plays a causal role in music-evoked reward, enhancing dopamine through levodopa and reducing dopamine through risperidone should lead to opposite effects regarding musical pleasure and motivation. In line with their prediction, they found that administration of levodopa and risperidone led to opposite effects: levodopa led to an increase in the experience of ‘chills’ or goose bumps, a common indicator of musical pleasure, while risperidone resulted in a decrease in chills. Electrodermal activity and participants’ ratings also indicated that they experienced an increase in pleasure when listening to music following dopamine enhancement and a decrease in pleasure following dopamine impairment. In contrast to much of the animal literature, this suggests that dopamine causally influences the hedonic pleasure experienced while listening to music. Participants bid significantly more money for songs under levodopa than risperidone, indicating that dopamine is also causally involved in motivational reward responses. The dopamine-induced changes in reward responses were paralleled by those observed in the control Monetary Incentive Delay task, suggesting that the effects seen while listening to music were a result of dopamine’s modulation of the reward system rather than of more general processes.
What's the impact?
This study is the first to show that dopamine function is causally related to the pleasure we experience from music, influencing both hedonic pleasure and motivation. More broadly, these findings begin to shed light on the more complex role the human dopaminergic system plays in abstract rewards. Musical pleasure also depends on additional affective and abstract cognitive processes (e.g. episodic memory). Given these additional processes also rely on dopaminergic transmission, further research is needed to determine whether dopamine generates the hedonic and motivational responses to music or whether it interacts with other neurotransmitter systems (e.g. the opioid system) to generate such responses.
Ferreri et al. Dopamine modulates the reward experiences elicited by music. PNAS (2019). Access the original scientific publication here.