|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.
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.