My, what big eyes you have – you must be trying really hard. A study of how pupils dilate with physical effort could allow us to make strenuous tasks seem easier by zapping specific areas of the brain.
We know pupils dilate with mental effort, when we think about a difficult maths problem, for example. To see if this was also true of physical exertion, Alexandre Zenon at the Catholic University of Louvain in Belgium, measured the pupils of 18 volunteers as they squeezed a device which reads grip strength. Sure enough, the more force they exerted, the larger their pupils.
To see whether pupil size was related to actual or perceived effort, the volunteers were asked to squeeze the device with four different grip strengths. Various tests enabled the researchers to tell how much effort participants felt they used, from none at all to the most effort possible.
Comparing the results from both sets of experiments suggested that pupil dilation correlated more closely with perceived effort than actual effort.
Mind over matter
The fact that both mental effort and perceived physical effort are reflected in pupil size suggests there is a common representation of effort in the brain, says Zenon.
To see where in the brain this might be, the team looked at which areas were active while similar grip tasks were being performed. Zenon says they were able to identify areas within the supplementary motor cortex – which plays a role in movement – associated with how effortful a task is perceived to be.
Next, they used a non-invasive method called transcranial magnetic stimulation to block activity in that area as people repeated the task. "When we disrupted this area, there was a clear drop in the perception of effort," says Zenon. In other words, the participants made the same actual effort but to them, it seemed significantly easier.
The implications are really interesting, says Zenon. "I don't know how practical it would be to use stimulation to make some activity seem less effortful, but in theory it's possible. For now, we are just trying to understand what mental effort actually is."
Journal reference: Frontiers in Behavioral Neuroscience, DOI: 10.3389/fnbeh.2014.00286
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