What is there in music that brings pleasure to us? Is it the lyrics, the tone, or the chords? The answer probably is all of these. Brain researchers have been engaged in finding out how the brain decides whether a musical pattern is pleasing or not. The pleasure decision of the brain lies in something known as reward processing. The reward system in the brain consists of a group of neural structures that are responsible for giving rise to positively-valenced emotions. In simpler words, the reward circuit of the brain provides us the feeling of pleasure after we have performed a certain task. Apart from pleasure, this neural system of the brain has other roles to perform. However, in musical pleasure, the reward system plays a pivotal role.
Recent researches suggest that musical pleasure come from positive reward prediction, which means, what we hear in musical form appears to be pleasant when it is better than what is expected. In fact, a manipulation of the listener’s expectation is a key mechanism through which music elicits pleasure. When we hear a song for the first time, the brain automatically predicts what sound will come next based on the music we have heard in the past. We experience pleasure when our expectations are met, but not all the time.
Carrying forward this stream of research, a recent finding from the Max Planck Institute of Human Cognition and Brain Sciences reported that two mechanisms are intricately related to musical pleasure arousal. The research on how chords involved in a musical note evokes pleasure was published in Current Biology, a Cell Publication. The two distinct patterns associated with chord pleasantness are: those with low uncertainty and high pleasure, or the opposite, that is high uncertainty but not surprising.
The team involved in the study adopted a combination of computational and brain imaging approach. The computational component was a machine learning system – a statistical model. The model was trained to quantify the expectancy of 80,000 chords from famous American Billboard hit numbers. This allowed the team to test whether pleasantness can be predicted by the uncertainty concerning the upcoming chord or the surprise experienced by hearing it. If a participant was sure what chord was coming next, that is low uncertainty, but the song unexpectedly deviated and surprised the listener, the musical pattern was found to be pleasant. On the other hand, if the chord progression was harder to predict, that is high uncertainty, and the actual chord which arrived did not surprise the listeners, even then the song appeared pleasant.
“In other words, what is crucial is the dynamic interplay between two temporally dissociable aspects of expectations: the anticipation beforehand, and the surprise afterwards,” said Vincent Cheung, the lead scientist of the study.
For deciphering the underlying neural mechanism, the team used the technique of brain imaging. Using FMRI, the researchers could examine the participants’ brain activity while listening to the music. The brain image showed that the interactive effect between the uncertainty of the upcoming chord and the level of surprise was associated with brain activity changes in emotion and auditory related areas. Precisely, activity in the brain areas of amygdala, hippocampus, and auditory cortex reflected the interaction and the other brain part known as the nucleus accumbens is associated with only uncertainty. Previously, nucleus accumbens was thought to have played a pivotal role in musical pleasure, which is, however, challenged by this study.