Last updated May 29, 2018 at 9:55 am
More bad news for those with a distaste for exercise. It might make you smarter.
A mouse running on a treadmill . The bell to represents the Pavlovian conditioning, and the landscape echoes the anatomy of the cerebellum. Credit: Gil Costa
Neuroscientists from Portugal’s Champalimaud Centre for the Unknown have shown that the more quickly mice run, the better learners they are. And while they can’t say for sure that the same applies to humans, it may explain why sometimes pacing around the room helps us come up with an answer to a tricky problem.
As the first author of the study Catarina Albergaria notes: “The cerebellum is a well-conserved structure across species and there are circuits that are common across species.”
An unexpected finding
The finding was serendipitous because the researchers were actually studying something else. Their initial goal was to relate cellular plasticity in the brain to learning, and try to understand how neural circuits in the cerebellum are changed by the learning of a motor task.
They ran experiments in which mice running on a treadmill had to learn to close their eyelids in response to a light, which was flashed right before they received an air puff to the eye which normally evokes a reflexive blink. This is a form of learning that takes place in the cerebellum.
However, these experiments didn’t work, largely because of “contaminant noise”. There was too much variability in the data they obtained from different mice and even from trial to trial from the same mouse.
This was confusing until they realised that the mutant mice they were using couldn’t run very well. When running speed was taken into account, the “noise” cleared. When all the animals were set to run at the same faster speeds, they had similar learning curves and maximum eyelid conditioning performance.
This confirmed that there was a causal link between running speed and enhanced learning, not just a correlation. The team then showed that once the mice had learned the task, their subsequent performance of the task still depended on their running speed.
“The mice performed less well when we slowed down the treadmill, and this happened at time scales of a few seconds”, Albergaria said.
Mossy fibres in the cerebellum
Their next question was: where in the brain is this enhancement happening? The team trained the mice to close their eyelids when experiencing other types of sensory stimuli (such as hearing a tone or feeling a vibration on their whiskers) before the air puff and found the same effect.
This told them that the neural process driving the learning enhancement was independent of the sensory system involved, suggesting that it might take place after the sensory signals had been processed by visual, auditory or tactile areas in cerebral cortex. So they turned to the cerebellum.
Using the technique of optogenetics, which allowed them to directly stimulate specific neurons with laser light, they stimulated neurons that project to the cerebellum through axons dubbed mossy fibres.
“We substituted motor activity with direct stimuli to the cerebellum and we found that if you are able to increase the activity of the mossy fibres, you enhance learning”, Albergaria said.
One implication of their findings, she adds, is that it doesn’t necessarily need to be locomotion; anything that drives an increase in mossy fibre activity could provide an equivalent modulation of learning.
“We tend to think that to manipulate the plasticity of the brain, so that people learn faster and slow learners improve, we have to use drugs”, said Megan Carey, who led the research. “But here, all we had to do was control how fast mice were running to obtain an improvement. It would be interesting to see if this holds for humans, for cerebellar forms of learning – and even for other types of learning.”
The paper published in Nature Neuroscience.
