http://www.dartmouth.edu/~news/releases/dec02/melodies.shtml
MELODIES IN YOUR MIND
Researchers map brain areas that process tunes
HANOVER, N.H. Researchers
at Dartmouth are getting closer to understanding how some melodies have
a tendency to stick in your head or why hearing a particular song can bring
back a high school dance. They have found and mapped the area in your brain
that processes and tracks music. Its a place thats also active during
reasoning and memory retrieval.
The study by Petr Janata,
Research Assistant Professor at Dartmouths Center for Cognitive Neuroscience,
and his colleagues is reported in the Dec. 13, 2002, issue of Science.
Their results indicate that knowledge about the harmonic relationships
of music is maintained in the rostromedial prefrontal cortex, which is
centrally located, right behind your forehead. This region is connected
to, but different from, the temporal lobe, which is involved in more basic
sound processing.
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The orange and red area indicates
where Janata and his collegues tracked and mapped musical processing in
the brain. The blue and purple areas are also processing music, but these
areas did not track the harmonic changes as consistently as the red and
orange areas.
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This region in the front
of the brain where we mapped musical activity, says Janata, is important
for a number of functions, like assimilating information that is important
to one’s self, or mediating interactions between emotional and non-emotional
information. Our results provide a stronger foundation for explaining the
link between music, emotion and the brain.
Using functional magnetic
resonance imaging (fMRI) experiments, the researchers asked their eight
subjects, who all had some degree of musical experience, to listen to a
piece of original music. The eight-minute melody, composed by Jeffrey Birk,
Dartmouth class of 02, when he was a student, moves through all 24 major
and minor keys. The music was specifically crafted to shift in particular
ways between and around the different keys. These relationships between
the keys, representative of Western music, create a geometric pattern that
is donut shaped, which is called a torus.
The piece of music moves
around on the surface of the torus, so we had to figure out a way to pick
out brain areas that were sensitive to the harmonic motion of the melody,
explains Janata. We developed two different tasks for our subjects to
perform. We then constructed a statistical model that separated brain activation
due to performing the tasks from the activation that arose from the melody
moving around on the torus, independent of the tasks. It was a way to find
the pure representation of the underlying musical structure in the brain.
The two tasks involved 1.)
asking subjects to identify an embedded test tone that would pop out in
some keys but blend into other keys, and 2.) asking subjects to detect
sounds that were played by a flute-like instrument rather than the clarinet-like
instrument that prevailed in the music. As the subjects performed the tasks,
the fMRI scanner provided detailed pictures of brain activity. The researchers
compared where the activation was on the donut from moment to moment with
the fluctuations they recorded in all regions of the brain. Only the rostromedial
prefrontal area reliably tracked the fluctuations on the donut in all the
subjects, therefore, the researchers concluded, this area maintains a map
of the music.
Music is such a sought-after
stimulus, says Janata. Its not necessary for human survival, yet something
inside us craves it. I think this research helps us understand that craving
a little bit more.
Not only did the researchers
find and map the areas in the brain that track melodies, they also found
that the exact mapping varies from session to session in each subject.
This suggests that the map is maintained as a changing or dynamic topography.
In other words, each time the subject hears the melody, the same neural
circuit tracks it slightly differently. This dynamic map may be the key
to understanding why a piece of music might elicit a certain behavior one
time, like dancing, and something different another time, like smiling
when remembering a dance.
Janata adds, Distributed
and dynamic mapping representations have been proposed by other neuroscientists,
and, as far as we know, ours is the first paper to provide empirical evidence
for this type of organizational principle in humans.
Arthur Magazine 