Frontal cortex oscillations in learning
When we learn the frontal part of our brain becomes active. When brain areas communicate with each other during learning, rhythmic patterns (oscillations) can be measured with EEG (read more about EEG in the Neuroscience Methods section). Previous studies have reported about both slow -theta- oscillations and fast -beta- oscillations in relation to learning.
Using tACS these rhythmic patterns can be specifically stimulated (read more about tACS in the Neuroscience Methods section). In two experiments we stimulated slow (experiment 1) and fast (experiment 2) oscillations, to see if and how they relate to learning.
I presented this project at the 6th Annual Brain Stimulation and Imaging Meeting, which you can watch online! If you like to, click the Presentation button below.
Methods experiment 1
Participants performed a so-called reversal learning task. They made a choice between a high and low number. Initially, the high number leads more often to a reward than the low number. People figure this out pretty quickly and mostly choose the high number. However, at some unpredictable point, the low number leads more often to a reward. Participants then need to reverse their strategy by opting for the low number to get the most rewards. After yet another while the best option reverses back to the high number.
While participants did this task the slow oscillations of the frontal part of the brain was stimulated with tACS or a placebo (sham). Additionally, we measured EEG before and after the task.
Results experiment 1
Participant learned significantly faster when tACS as applied compared to placebo. However, in the end participant receiving tACS did not choose the high number as often as those who received placebo. EEG showed that tACS did not merely affect slow oscillations, but had an effect on the interaction between slow and fast oscillations.
Methods experiment 2
The second experiment was almost identical to the first experiment. The same task was used. tACS was applied this time at a fast (beta) frequency. Also, the specific way in which we placed the electrodes of tACS differed a little from experiment 1. Therefore, we had two conditions with real stimulation and one placebo condition. Eventually, we found no difference between the two real stimulation conditions.
Results experiment 2
In contrast to experiment 1, tACS on fast oscillations did cause faster learning. However, participant receiving tACS did choose more high numbers in high blocks and more low numbers in low blocks. As in experiment 1, on the EEG we found that tACS had an effect on the interation between slow and fast oscillations.
Learning has two aspects. First, how quickly you learn something. Second, how well you implement what you learned. Stimulating slow oscillations in the frontal part of the brain made participant learn faster compared to a placebo condition. However, the implementation of what they learned was worse, since they did not choose the high number consistently when this was the best option.
Stimulating fast oscillations in the frontal part of the brain improved the implementation of learning. They more consistently choose the best option compared to people receiving placebo stimulation. However, promoting fast oscillations did not make them learn faster.
Our two studies show how slow and fast oscillation in the frontal cortex relate to different aspects of learning. Also, it shows that brain stimulation can improve certain aspects of cognition. But, this will be at the cost of other cognitive aspects. Our brain has limited resources, which can be biased with tACS. But tACS does not make us super-human.
Wischnewski, Joergensen, Compen & Schutter (2020). Frontal beta transcranial alternating current stimulation improves reversal learning. Cereb Cort, 30(5), 3286-3295. https://doi.org/10.1093/cercor/bhz309
Wischnewski, Zerr, Schutter (2016). Effects of theta transcranial alternating current stimulation over the frontal cortex on reversal learning. Brain Stimul, 9(5), 705-711. https://doi.org/10.1016/j.brs.2016.04.011