For 1 week, 13 people were tested on dissimilar metrics of intelligence

One week seems very short compared to the studies. I didn't check all, but one mentioned in Wikipedia was 5 weeks and another whose abstract I found was 4 weeks. It seems probable that any effects on the brain would be slow to accumulate. As a point of comparison, it takes a lot longer than one week to assess the value of a particular muscle training program.