Most people appreciate music without stopping to wonder how the musical structure behind melodies is represented in their brains.
But Petr Janata, Research Assistant Professor at Dartmouth's Center for Cognitive Neuroscience, has made it his job to know exactly that.
Janata's research, published in the Dec. 13, 2002, issue of the journal Science, not only reveals a neurological basis for musical structure in the brain, but also may provide explanations for such phenomena like the spontaneous recollection of melodies, and the dynamic association of music with certain memories.
Subjects of Janata's study listened to a melody that systematically moved through all 24 major and minor keys while they performed a number of cognitive tasks. Functional Magnetic Resonance Imaging revealed that the perceptual patterns of the music consistently activated a region in the front of the brain known as the rostromedial prefrontal cortex.
For purposes of the experiment, the surface of a donut-shaped figure, known as a torus, geometrically represented the perceptual relationship between keys of Western music. The music used for the study was composed to move along the surface of the torus as it moved through the 24 major and minor keys.
As the torus model was being activated by the music, researchers could observe which brain areas were being activated at the same time. "So we essentially ask what brain areas are tracking the melody as it moves around on the surface of the torus," Janata said.
But Janata and his colleagues had not expected to find an organized topographic map of such a complex input as musical structure.
"When we looked at our activation patterns we saw, not to our surprise, a network of areas that were active," Janata said. "But this one region that was consistently activated, the rostromedial prefrontal cortex -- that was a bit of a surprise."
Janata explained that the rostromedial prefrontal cortex has been associated with a variety of other functions such as the processing of emotional and cognitive information, maintaining a sense of self, and spontaneous thought. This could possibly explain why songs "pop into our heads."
The scientific evidence also helps explain how we are able to detect "wrong notes" --notes that don't fit their musical context -- since now a neurological basis for musical structure has been discovered.
"If we didn't have any way of structuring the music in our minds, it would all just be a random jumble of sounds," Janata said. "So the mere fact that we recognize styles of music or have preferences for styles of music suggest that our brains learn that structure through constant exposure."
In fact, this may be one of the first studies that suggests how a cognitive structure, such as a mental map of something as intricate as the relationship between musical keys, is represented in the brain.
Janata and company also stumbled upon another discovery: they noticed that the representation of the musical structure would reconfigure itself from session to session.
"If you look at the selectivity for different keys across sessions, the same circuit is active but different parts of that circuit may be maximally sensitive to different keys on different days," Janata said.
This suggests the occurrence of dynamic topography, a theoretical concept that Janata's study may be one of the first to provide evidence for.
"Theorists have suggested it, but there hasn't been really any empirical evidence," Janata said. "There is still a lot of work that needs to be done to really firmly establish that concept."
According to Janata, the dynamic topography may reflect how the circuits configure themselves in order to bind different pieces of information together in a context-dependent fashion. This helps to explain why a certain song may be associated with different memories at different times.
Janata also shared various speculations regarding why, in an evolutionary sense, we have the capacity for mapping musical structures in the brain. He first suggested that music and language are patterns of sound that co-evolved.
"Perhaps musical processes and the ability to detect pitch contours in melody is similar in some way of tracking the contours of prosody in speech," Janata said.
He also speculated that our brain is attracted to detecting patterns in the environment.
"Music is a really neat patterning of our auditory environments," Janata said. "I think our brains like something about having patterns in the environment that they can understand and appreciate the aesthetics of, but they aren't so simple as to be boring. So music fits that intermediate level of complexity, that our brains can comprehend and find pleasing."
The study has also inspired new curiosities, including curiosity into a cross-cultural aspect, since the study was conducted using only a Western tonal representation.
"Cross-cultural studies let you get at this issue of how much of these representations are learned and how much of them are intrinsic." Janata said.
Additionally, Janata expressed interest in finding topographic representation in the brain for musical styles.
