Uncertainty helps the brain to learn
In a nutshell: Adding uncertainty to an established brain-stimulation method may boost its effectiveness.View Paper Abstract
Some current theories propose that uncertainty can enhance learning. Think about it this way: if you know exactly what the consequence of a certain action is, there’s nothing new for you to learn. But if there is a mismatch between what you predict and what actually occurs, your brain needs to adjust and improve its prediction for next time – that’s learning!
Several methods can be used to test how the brain learns. For example, a non-invasive brain stimulation technique called transcranial magnetic stimulation (TMS) used on a brain region that controls a muscle can generate a small twitch in that muscle. Similarly, if a small electrical current is applied to the nerve innervating a muscle, some of that electrical activity travels up to the brain area that controls that muscle. A method called PAS (paired associative stimulation) pairs these two stimuli by injecting a current into the muscle’s nerve just before applying a TMS pulse to the brain. The regular pairing of these two stimuli normally increases the size of the resulting muscle twitch for more than an hour following the procedure, which reflects a process in the brain thought to underlie learning.
Research Fellow Martin Sale, Brain Function CoE Chief Investigator Jason Mattingley, and their colleague Abbey Nydam from The University of Queensland wanted to see if introducing uncertainty into PAS boosted its effects. The team presented participants with a random combination of paired (muscle and brain) or unpaired (brain only) stimuli. Before each one, the participants also heard a sound that related to whether the upcoming stimulus was paired or unpaired (no uncertainty) or gave no indication (maximum uncertainty). Participants weren’t told what the sounds meant, although some of them figured out the relationship.
The team gauged the effectiveness of the modified PAS by measuring the size of the muscle twitch before PAS, and 5 and 15 minutes afterwards.
Compared to the pre-PAS level, the average size of the muscle twitch increased under both the no uncertainty and maximum uncertainty conditions – which would be expected for PAS. However, the increase in size 15 mins after PAS was significantly higher for the maximum uncertainty condition. These effects were the same regardless of whether the participants were aware of the relationship between the sounds and the stimuli.
The discovery that the size of the effect increases when uncertainty is incorporated into PAS supports other researchers’ findings that stimulus uncertainty helps learning. The team’s results also suggest that adding uncertainty to PAS could increase its effectiveness, potentially making it a more reliable treatment tool in clinical neuroscience.
The team hopes to apply its findings to neurorehabilitation, to see if introducing uncertainty can enhance the brain’s ability to recover from injury.
Sale, M. V., Nydam, A. S., & Mattingley, J. B. (2017). Stimulus uncertainty enhances long-term potentiation-like plasticity in human motor cortex. Cortex, 88, 32–41.
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