In a nutshell: Researchers have discovered that transcranial direct current stimulation interacts with learning to affect behaviour.

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Stimulating the brain by applying a weak electrical current – using non-invasive methods such as transcranial direct current stimulation (tDCS) – can affect behaviours such as motor learning, decision-making, and multi-tasking ability. However, the effects of tDCS can vary significantly, both within and between individuals, which limits it application.

Understanding what causes this variability could enable tDCS to be used more broadly – for example, to manage the cognitive deficits that accompany many psychological disorders.

Studies have shown that tDCS can affect learning. When we learn, our brains adapt in response. They do this by changing the structure of brain cells or the connections between them. Brain Function CoE investigators wondered if the opposite might also be true – could learning affect tDCS? Differences in the level of learning in a particular task – and the extent of the resulting brain changes – might explain the variations in tDCS’s effects.

To find out, investigators Daniel Fehring and Farshad Mansouri from Monash University and their colleagues tested participants on a particular task before and after applying tDCS. The tests were repeated a week apart.

Over the course of testing, the participants’ performance on the task confirmed that they were learning from one week to the next. The researchers found that learning was much greater when tDCS was applied in the first week than when it was applied in the second week – indicating that the effects of brain stimulation depend on the level of learning in the task.

The researchers’ findings could help to adjust the dosage and frequency of tDCS depending on the level of learning in a particular task. This could reduce the variability in the effects of tDCS, making brain stimulation more predictable and beneficial for the treatment of psychological conditions.

Next steps:
The researchers plan to further study how changing the way tDCS is applied – for example, by varying its type, intensity or duration – might influence its effects on behaviour. They will also investigate whether other factors, such as the type of learning or an individual’s sex, have an effect.

Fehring, D. J., Illipparampil, R., Acevedo, N., Jaberzadeh, S., Fitzgerald, P. B., & Mansouri, F. A. (2019). Interaction of task-related learning and transcranial direct current stimulation of the prefrontal cortex in modulating executive functions. Neuropsychologia, 131, 148–159. doi: 10.1016/j.neuropsychologia.2019.05.011

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