Some people are born without the corpus callosum, a structure residing between the two halves of the brain that facilitates communication between them. This is called “Agenesis of the corpus callosum” (AgCC) and is extremely rare but fairly well-studied. Older readers may remember that it used to be thought that an appropriate treatment for epilepsy was to cut the corpus callosum, effectively cutting off a large percentage of the communication between the two hemispheres of the brain, and it was research on these “split-brain” patients that led to the fascinating discovery that the two halves of the brain process information differently, and was the origin of the “left-brain/right-brain” popular thinking about the way we process information.
Corpus Callosum of Brain
Although I’d known about musicians having a thicker corpus callosum than the average, my interest was rekindled by an article corresponding to an episode of “Curious” I saw on my local PBS station some while back :
Normally, the corpus callosum matures and becomes more efficient as children approach adolescence, allowing abstract reasoning, problem solving, and socialization to develop rapidly. This does not occur in children with AgCC; consequently, they fall behind their peers mentally and socially as they proceed through their teens and into adulthood. People with AgCC may be oblivious to the social consequences of their own behavior and typically do not pick up on the social cues of others. They may fail to comprehend jokes or figures of speech, tending instead to interpret communication literally. They are also not as effective as their peers in recognizing emotion in people’s faces, and they are often extremely gullible.
And now, two more studies :
In 1994 Discover magazine published an article which discussed research by Gottfried Schlaug, Herman Steinmetz and their colleagues at the University of Dusseldorf. The group compared magnetic resonance images (MRI) of the brains of 27 classically trained right-handed male piano or string players, with those of 27 right-handed male non-musicians. Intriguingly, they found that in the musicians planum temporale – a brain structure associated with auditory processing – was bigger in the left hemisphere and smaller in the right than in the non-musicians. The musicians also had a thicker nerve-fiber tract between the hemisphere [sic]. The differences were especially striking among musicians who began training before the age of seven.
According to Shlaug, music study also promotes growth of the corpus callosum, a sort of bridge between the two hemispheres of the brain. He found that among musicians who started their training before the age of seven, the corpus callosum is 10-15% thicker than in non-musicians.
At the time, Schlaug and other researchers speculated that a larger corpus callosum might improve motor control by speeding up communication between the hemispheres.
Since then, a study by Dartmouth music psychologist Petr Janata published by Science in 2002, has confirmed that music prompts greater connectivity between the brains [sic] left and right hemisphere [sic] and between the areas responsible for emotion and memory, than does almost any other stimulus.
Janata led a team of scientists who reported some areas of the brain are 5% larger in expert musicians than they are in people with little or no musical training, and that the auditory cortex in professional musicians is 130% denser than in non-musicians. In fact, among musicians who began their musical studies in early childhood, the corpus callosum, a four-inch bundle of nerve fibers connecting the left and right sides of the brain, can be up to 15% larger.
What does this “mean”? We don’t know, but it leads to some fascinating speculation. If people born without a corpus callosum lack normal social skills, does that mean that people who have a larger, thicker corpus callosum have better-than-average social skills? Are they less gullible? Do they better understand the social consequences of their actions? Do they have more “emotional intelligence”? Are they better at abstract reasoning? And what about the auditory cortex? If it’s 130% denser, what does that mean for spoken-language processing? For awareness of one’s surroundings?
See the Neuroanatomy page for an explanation of what the various affected parts of the brain do.