Effect of Odorant Presentation on Changes in Cognitive Interference and Brain Activity during Counting Stroop Task

Cognitive task for longer duration increases subject´s psychological loadings because of extracting ordered answer from visual stimuli. The present study investigated how intermittent odorant presentation during cognitive task contributes to cognitive function and statement of psychological loadings. We asked ten male subjects to perform counting stroop task that repeatedly counts the pieces of digits displayed on a monitor. The task consisted three tasks that the digits and the number were consisted (task1), non-consisted (task2), and both the former tasks combined (task3). The duration of each task was four minutes, and thus subjects totally performed the tasks for 12 minutes. Four kinds of odorant stimuli (non-odor, lemon, peppermint (pmint), and skatole (ska)) were used in this study and each odor was presented after beginning of each task for one minute. Behavioral results, rate of content of α, β, δ, and θ waves from EEG, and oxygenated hemoglobin concentration (ΔO₂Hb) were measured and compared between each odor condition. Behavioral results, the reaction time and the percentage of questions answered correctly, ΔO₂Hb in right hemisphere related to pleasant emotion, and rate of content of α wave were significantly increased when pmint and ska were presented. The findings indicated that intermittent odor presentation induced pleasant emotion and increased cognitive function and state of concentration, regardless of odors.