Look ma, both hands
Hands. As a species, we humans take pride in our opposable thumbs and our penchant for maneuvering our digits to perform complicated tasks (writing, playing musical instruments, sports). We’re also obsessed with handedness (with the inevitable majority/minority valence - right handed majority: good; left handed minority: bad). But is our focus on handedness ignoring the most important function of our ten, bendy offshoots?
Beyond the dichotomy of left and right-handedness, we do many things that require us to coordinate both of our arms. This is called bimanual coordination, and it’s a complicated task for our brains. Of course, those of us struggling on the dance floor with two left feet will know that this is a complicated task for our feet as well, but here we will focus on our hands.
Coordination of limbs is an evolutionarily ancient skill, shared by both vertebrates and invertebrates alike. All animals that use limbs to walk or swim or fly do so in a coordinated fashion. For us humans, taking part in many activities such as sports or music mean using our limbs in context-dependent ways.
Consider the pianist. She presses on smooth black and white keys, hundreds of muscles are whirring away inside her body, and her brain is performing complicated emotional and analytical processes. Although every independent movement of the pianist’s hands is one she’ll make while doing other tasks, their coordination yields a unique product: music. The pianist’s strategies to generate and optimize her performance are constrained by her muscular and nervous systems. Coordinating her right and left hands is just one of the tasks her brain needs to carry out while playing music. Most piano music requires your left and right hands to perform radically different motor tasks (with varying degrees of complexity; Bach is a particularly good example of hands going in opposite directions).
Symmetric bimanual movements are more natural and easier than parallel movements. Brain activation supports this, as there is more activation during parallel movements, suggesting that this task requires more mental energy, so to speak.
What is happening in the brain during complicated bimanual performances such as piano playing? And does this brain activation change depending on how much an individual has practiced complex bimanual tasks?
Peering into the brains of pianists
Bernhard Haslinger and his colleagues at the Neurologische Klinik in Munich used brain imaging to try and answer this question. Utilizing an fMRI machine, which determines brain activity indirectly by measuring the amount of oxygen the brain is using, Dr. Haslinger scanned the brains of 12 professional and 12 naïve piano players while they did finger movements with both hands. Their movements were either in-phase, symmetric, or out of phase, parallel.
In professional pianists, brain activation is lower overall compare to naïve players, when making complex bimanual finger movements. This finding suggests that for the pros, complex bimanual movements, require less “mental energy” than for naïve players. Similarly, the professional’s brains are equally activated while generating symmetric and parallel movements, suggesting that their training has overcome our natural inclination toward symmetric movement.
The functional differences between naïve and professionals manifest themselves in structural differences in the brain. The right and left hemispheres of the brain are bridged by a structure called the corpus callosum, which carries signals between the two sides of our brain. This communication is part of what enables us to coordinate bimanual movements. Logically enough, structural differences between naïve and professional musicians show up in the corpus callosum. Professional pianists have both a larger corpus callosum and also less trans-callosal inhibition, or inhibition occurring across the corpus callosum. These increased connections make them more efficient at certain bimanual movements.
How did the professionals end up with these increased connections? Music learning is often begun at an early age, when the brain is most plastic, meaning its connections are most able to change. Perhaps the increased size of the corpus callosum is thus due to early demands for complex bimanual coordination amongst the professionals. But early training is likely not the only factor differentiating the brains of professional and naive pianists, as intense music playing can also drive structural changes in the adult brain (see here and here).
There are also individual differences among pianists, which might be explained by different strategies they use to learn non-symmetric bimanual movements. Pianists can either practice each hand separately, or practice with both hands starting from the beginning. These two strategies represent a major debate in theories of bimanual movement. Is there a unifying motor plan that both hands use, or are there two independent plans that work together to produce one movement?
So the next time you nestle into a red, velvet seat in a grand concert hall, perhaps you will be reminded that beneath the lightning fast, agile finger movements, complex processes are happening inside the brain of the performer.