Reacción a "Electrical brain stimulation could improve mathematics learning in people with more difficulties"

This is a strong study with a rigorous methodology. The distinction between calculation and memorization is well-established and the training program works well to produce each type of learning. The brain areas stimulated, frontal and parietal cortex, are important for math cognition. The only concern is the sample size as noted below. 

This work is important because it provides causal evidence about the role of frontal-parietal connectivity in math learning. We know from prior work that adults with stronger frontal-parietal connectivity tend to have better math skills, but we don’t know which if the better connectivity helped them learn math or if learning math well increased their connectivity. This works shows that altering frontal activity with brain stimulation improved math learning in those with low connectivity, suggest the connectivity differences are driving learning differences. The exciting part is that these results suggest that changing connectivity with stimulationcould unlock learning potential in struggling students. 

[Regarding possible limitations] While the overall sample size is relatively large for this kind of work and reasonable for examining the main question, I would say it’s under powered for examining the effects of brain changes with learning and stimulation.