Dietary nitrate modulates cerebral blood flow parameters and cognitive performance in humans

Wightman EL, Haskell-Ramsay CF, Thompson KG, Blackwell JR, Winyard PG, Forster J, Jones AM, Kennedy DO (2015) Dietary nitrate modulates cerebral blood flow parameters and cognitive performance in humans: A double-blind, placebo-controlled, crossover investigation. Physiology & Behavior, 149:149-158.

A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood
Effects of resveratrol alone or in combination with piperine on cerebral blood flow parameters and cognitive performance in humans