Brain Activity: Is Less More?

Areas of the brain that show a decrease in activity upon learning a task (from Chein and Schneider, 2005)

Imagine an experiment where scientists are using fMRI to look at activity in a person’s brain before and after the person learns how to do a particular task. (The task itself doesn’t matter too much right now, but it could be something like tapping a particular sequence of fingers, or reading backwards, or picking out pictures of dogs hidden in a complicated landscape.) The scientists scan the person’s brain while she is doing the task for the very first time. Then they have the person practice doing the task until she's really good at it. Finally, the person gets scanned again, while performing this well-learned task. What do you think the difference will be in the person’s brain activity? Would you expect to see more activity or less activity?

I’ve been slogging through scientific papers that look at changes in brain activity (using either fMRI or PET) when we learn skills, and growing increasingly puzzled. In some cases, when people learn to do something, there is more activity in their brains, and the researchers say: “See, that’s because they’re using more of their brains for this!” But sometimes there is less activity, and the researchers conclude that when we are good at something, our brains are more efficient.

Don’t those two things sound contradictory to you? Which is it? Do we use less brain power or more brain power when we’re good at doing a task? I’ve spent some time looking into this question, and when you get into the details, the answer is… it depends.

But it does make sense, trust me.

The best explanation that I found was in The Cambridge Handbook of Expertise and Expert Performance. There’s a chapter by Nicole Hill and Walter Schneider entitled “Brain Changes in the Development of Expertise: Neuroanatomical and Neurophysiological Evidence about Skill-Based Adaptations”. They suggest that when we learn a skill, there are a number of different patterns of changes in brain activity that are seen.

One of the most common patterns is a decrease in activity in parts of the brain that make up the control network. These are the parts of the brain responsible for working memory, attention, decision-making, and sequencing steps in a task. They’re active when we perform any task that isn’t well-learned, whether it’s a motor task, a perceptual task, or a reasoning task. When we gain experience with a task, we don’t need to devote as much concentration to it. We learn what steps follow which, and what is required to efficiently get the job done. Once we’re experienced at a task, the control network is not required to do as much work, so activity decreases in these areas of the brain.

A second pattern that is commonly seen is an increase in activity in parts of the brain specifically related to performing the task. For a motor task such as a sequence of finger taps, there is an increase in activity in the primary motor cortex of the brain (as shown by Avi Karni and colleagues in 1995). This is believed to be due to the recruitment of more neurons into the representation of the movement and supports the idea that networks of neurons in the primary motor cortex can code for sequences of movements. So when musicians are playing, there is a larger part of the primary motor cortex that is active, causing their hands to move in well-learned sequences.

A third pattern is known as functional reorganization, in which different areas of the brain are seen to be active when comparing novices vs. experts. For instance, in motor learning tasks such as learning a sequence of key-presses, when we initially are trying to learn the sequence, there is a lot of activity in the cerebellum, but once the sequence is well-learned, the cerebellum is much less active. Instead, there is an increase in activity in the striatum, a part of the brain believed to be responsible for (among other things) sequences of movements. Julien Doyon and colleagues, who reported this in 2002, conclude that the cerebellum has an important role in learning a motor task, but much less of a role in performing the task once it is well-learned.

All three patterns can be seen when learning different aspects of music, depending on what the learning task is. And sometimes all three patterns occur at the same time, so that we see a decrease in activity in control regions of the brain, an increase in regions specifically related to a task, and also some transfer of activity to regions that are not initially active. This is part of why it is so difficult to interpret data about activity in the brain. Understanding what each region of the brain does in relation to the task at hand allows us to tease apart the differences we see. And conversely, seeing how the activity changes in a particular area of the brain helps us understand how it contributes to learning and to performance of a skilled task.

References

Chein, J.M., and Schneider, W. (2005). Neuroimaging studies of practice-related change: fMRI and meta-analytic evidence of a domain-general control network for learning. Cognitive Brain Research 25,607–623.

Doyon, J., Song, A.W., Karni, A., Lalonde, F., Adams, M.M., and Ungerleider, L.G. (2002). Experience-dependent changes in cerebellar contributions to motor sequence learning. Proc. Natl. Acad. Sci. U.S.A. 99, 1017–1022.

Hill, N.M., and Schneider, W. (2006). Brain Changes in the Development of Expertise: Neuroanatomical and Neurophysiological Evidence about Skill-Based Adaptations. In The Cambridge Handbook of Expertise and Expert Performance, ed. Ericsson, K.A., Charness N., Feltovich, P.J., and Hoffman, R. R. (Cambridge University Press).

Karni, A., Meyer, G., Jezzard, P., Adams, M.M.,Turner, R., and Ungerleider, L.G. (1995). Functional MRI evidence for adult motor cortex plasticity during motor skill learning. Nature 377,155–158.

Ungerleider, L.G., Doyon, J., and Karni, A. (2002). Imaging brain plasticity during motor skill learning. Neurobiol Learn Mem 78,553–564.

Finger movements and tension

Try this: hold up your hand with your fingers extended, and then turn it so you’re looking at it side-on, with all your fingers lined up. Now bend your middle finger, trying to keep the others standing straight up. What you probably see as you move your middle finger is that your ring finger also moves out of place, no matter how much your try to keep it still. Your index finger probably moves a little too. Don’t get too stressed if it’s hard to move just your middle finger: our fingers are designed to move together. The thumb moves quite independently, but when we move each of the long fingers, other fingers also try to move.

When flexing one finger, the other fingers move out of place too.

There are two main reasons that this is true: first, each finger is connected to adjacent fingers by skin webbing, tendons, and muscle fascia, so that when we move one finger, it pulls on its neighbours. The second and more relevant reason is that our muscle control of our fingers is not completely separate.

You might think that motor control of our fingers works like this: a certain area of our brain is responsible for each finger. When that part of the brain is active, a message gets sent to the muscle responsible for that finger, which causes that finger to move. In this simple scenario, there is a straight line connection between 1 brain area, 1 muscle, and 1 finger. Unfortunately, this is not how finger control works.

The neurons that send motor commands to our finger muscles are located in the hand area of the primary motor cortex. But there is not a separate area for each finger. Studies looking at which neurons control which finger movements have found that the neurons that control the separate fingers are all kind of jumbled together. Also, a lot of the neurons that were studied were found participate in the control of more than one finger.  

This idea of mapping neurons onto finger movements gets even more complicated when you look at the muscles that move our fingers. The muscles responsible for flexing (bending) and extending (straightening) our fingers are located in our forearms, and connect to the finger bones through tendons which go through our hands. But there are not separate sets of muscles for each finger.

In fact, there are only two muscles that control flexing the four long fingers: the flexor digitalis profundus and the flexor digitalis superficialis. Each of these muscles has four tendons, one connecting to each of the long fingers of the hand. The muscle has different sections (known as muscle bellies) that each primarily activate one finger, but they are not completely separate, and they also often contract together, since the neurons that activate the muscles don't act independently either.

 

Similarly, to extend the fingers, there is one main muscle:  the extensor digitorum communis, involved in extending all four long fingers. There are also two smaller muscles:  the extensor digitali minimi (extends the little finger) and the extensor indicis (extends the index finger).

If we don’t have separate muscles controlling each finger, how do we move them independently?   The most likely possibility is that we move our fingers individually due to the combined action of more than one muscle, each of which has different amounts of control over each finger.  This conclusion comes from the lab of Marc Schieber at the University of Rochester, who showed in 1995 that when monkeys move their fingers individually, more than one muscle is active, and the amount of muscle activity in each muscle is different for the movements of each finger. 

In other words, when we try to move one finger independently, we don’t just contract a muscle to move that finger, we also have to contract other muscles to prevent the other fingers from moving. For example, raising the ring finger while keeping the middle finger still is difficult, because these fingers not only share a common extensor, but they are also joined mechanically. In order to raise just the ring finger, you need to activate the flexor going to the middle finger (in order to stabilize it), and at the same time activate the common extensor. It’s also really handy to extend the little finger at the same time, since this will pull on the ring finger and help it extend. See how complicated that is? No wonder moving our fingers individually is difficult.

Also, no wonder we can build up a lot of tension in our hands while playing musical instruments. It’s very common for children to play with their hands very tense. By maintaining activity in both the flexor and extensor muscles of the fingers, they can stabilize their finger joints and prevent unwanted movement. This strategy of co-contraction does work, up to a certain point. The problems very quickly outweigh the advantages: with too much tension in the hand, moving each finger is more work, and therefore quick and fluent movements of the fingers are impossible.

Here is a video of a young boy whom I teach who clearly has excess tension in his hand.  Notice how his fifth finger is extended as he plays.

 

This child’s problems with tension get worse as he tries to increase the tempo of his pieces. He is absolutely unable to play fast passages. This is typical of students with tension issues. Worse, excess tension leads to fatigue, pain, and eventually injury. Obviously, this situation is something to be avoided.

What’s not obvious is the best way to help students who have too much tension. When I do an on-line search, most of the advice (as in this article) is to re-align body and hand position, and then play simple exercises while focusing on mental awareness of tension in the hand, wrist, and arm. 

The good news is that our control over individual fingers is not set in stone:  we can learn to use different muscle strategies to move our fingers independently (as suggested in Winges & Furuya, 2015; Semmler et al.,  2004). This is part of musical training:  all those Hanon exercises for the piano (and Moyse studies for the flute, etc.) are designed to help us learn to efficiently control our finger muscles so that we can move fluently between different notes.

If you’ve had success in minimizing hand tension (either for yourself or your students), I’d love to hear about it in the comments.

References:

Schieber, M.H. (1995). Muscular production of individuated finger movements: the roles of extrinsic finger muscles. J. Neurosci. 15, 284–297.

Schieber, M.H. (2002). Motor cortex and the distributed anatomy of finger movements. Adv. Exp. Med. Biol. 508, 411–416.

Semmler, J.G., Sale, M.V., Meyer, F.G., and Nordstrom, M.A. (2004). Motor-unit coherence and its relation with synchrony are influenced by training. J. Neurophysiol. 92, 3320–3331.

Winges, S.A., and Furuya, S. (2015). Distinct digit kinematics by professional and amateur pianists. Neuroscience 284, 643–652.