Last updated January 11, 2018 at 10:43 am
If you’re right-handed and you’re given a pencil and asked to write with your left, you’ll struggle. As you scrawl away, your brain is working away behind the scenes, churning out new synapses, growing new cells, sprouting more branches and testing out new neuronal networks.
And all that activity results in changes that scientists can see – the grey matter, the part of your brain that has all the neurons and synapses between them, actually gets bigger. But there’s a limit, our brains don’t just grow endlessly as we learn new skills. Eventually the new cells and circuits are pruned away, leaving only the most efficient wiring behind.
“Brain matter volume increases in the initial stages of learning, and then renomalizes partially or completely,” says neuroscientist Elizabeth Wenger, a researcher at the Max Planck Institute for Human Development in Berlin.
She describes the process in terms of casting a movie: brain cells are aspiring actors looking for their big Hollywood break where the brain is the director. The brain calls in candidates by forming new cells, which leads to an increase in volume. They are then auditioned for the role, and the best candidates are selected while the rest are sent home (renormalization).
This implies that as we learn, there is a temporary increase in brain volume. This is backed up with several studies in animals and humans, and can occur quite quickly. In one study looking at people undergoing balance training, increases in cortical thickness were observed after 45 minutes of training. These changes weren’t visible after two weeks.
In the case where right-handed people were asked to practice left-handed drawing, there were detectable differences in grey matter volume after a month, but this was not seen another three weeks later.
The types of changes that are happening at the cellular level include growth of new neurons, glial cells (which provide support and protection for neurons), the formation and turnover of synapses (connections between neurons) and the length and number of dendrites, the branches of neurons that connect to each other. The researchers propose that the structural changes seen in MRIs is probably a complex mix of all of these processes.
The idea that brain pruning occurs is not a new one. It’s an established idea in early development. There is an enormous growth in the number of synapses in babies brains, which are gradually pruned away over childhood and adolescence.
This growth and shrinkage as we learn helps explain some previous unexplained findings in MRI studies investigating learning, where decreases in brain volume have been observed and often left unexplained. The researchers in this study suggest that it’s going to be really important to include more than two basic “before” and “after” time points when doing any experiments investigating brain changes with learning, so as not to miss this expansion and pruning trend.
Most of the experiments where the brain growth and shrinkage has been seen have been related to sensory or motor skills. Whether or not the same kinds of trends are seen for higher order cognitive learning like critical thinking or problem solving skills are yet to be explored.
Read the original paper from Trends in Cognitive Sciences