There is no evidence that consuming fructose has an unfavorable effect on cognitive abilities.
In fact, a study by Miller et al. (2013) found that consuming fructose resulted in comparable cognitive abilities as glucose without raising blood sugar levels as much as glucose. They also found that consumption of fructose produced similar executive functioning as consumption of glucose with a comparable number of anagrams being solved by both groups. The authors concluded that, “fructose (a sugar that has little effect on blood glucose levels, does not have reinforcing value post-ingestion, and inhibits cortical responding) can enhance executive control to the same degree as glucose” (Miller et al., 2013).