Tadashi NIIOKA^* and Makoto SASAKI

Graduate School of Environmental Earth Science, Hokkaido University, Kita 10 Nishi 5, Kita-ku, Sapporo 060-0810, Japan

(Received February 28, 2003; Accepted October 9, 2003)

A modified Stroop color-word task has been developed to activate the prefrontal cortex as a cognitive task and it has been tried to clarify whether change in the cerebral hemodynamics after ingesting caffeine is associated with change in performance on the modified Stroop task in young male subjects. In this modified task, subjects were instructed to quickly select a colored disk on a computer screen in response to an instruction, i.e. ''color'' or ''meaning'', presented simultaneously with one color word at each trial. The color of the presented color word was discordant with the meaning of the word. Relative changes in blood volume and oxygenation in the prefrontal association cortex were measured noninvasively using continuous-wave near-infrared spectroscopy. The results showed that caffeine ingestion decreased blood volume and oxygenated hemoglobin concentration in the brain during the modified Stroop task, and that the individual change in the latter was related to change in performance on the task following caffeine ingestion.

Key words: cognitive task, Stroop, task performance, cerebral oxygenation, cerebral activity, caffeine, human

^*Correspondence E-mail address: niioka@ees.hokudai.ac.jp