If you dig you can find research that indicates that caffeine is the most potent cognitive boosting chemical we know of to date. I think the first half of your

If you dig you can find research that indicates that caffeine is the most potent cognitive boosting chemical we know of to date. I think the first half of your point, that we're reducing blood flow to the brain, is a valid one. However, evidence indicates that whatever negative impact on cognition occurs are overpowered by the positive impacts. Another factor to consider is how much blood flow is correlated to cognitive abilities. Obviously some is needed, but after sufficient oxygen levels are reached I suspect other factors (such as glial cells) play stronger roles. Definitely a fascinating field of study.