Effects of Phytoncide Inhalation on Stroop Task Performance in Patients with Mild Cognitive Impairment: An fNIRS Pilot Study.

Objective: : Several studies have reported the therapeutic effects of phytoncides on various mental disorders. However, little is known about the therapeutic effects of phytoncides on mild cognitive impairment (MCI), a prodromal stage of dementia. In this pilot study, we aimed to clarify the effect of inhaled phytoncides on the cognitive function of patients clinically diagnosed with MCI.

Methods: : In total, 21 patients with MCI were randomly assigned to either a saline (no-odor) or phytoncide group and subsequently inhaled saline or phytoncide for 30 minutes indoors, respectively. To evaluate changes in cognitive function, we implemented functional near-infrared spectroscopy along with the Stroop task and compared task performance and hemodynamic responses in the dorsolateral/ventrolateral part of the prefrontal cortex (DLPFC/VLPFC) before and after inhalation.

Results: : While the saline group showed no significant difference in either task performance (Wilcoxon = 18.50, = 0.385) or hemodynamic response, a significant increase in Stroop task performance (Wilcoxon = 1.50, = 0.009) and hemodynamic attenuation in the left VLPFC (Wilcoxon = 56.00, = 0.042) were found in the phytoncide group after inhalation.

Conclusion: : Since compensatory task-related prefrontal hyperactivation represents one of the neural indicators of cognitive dysfunction in MCI, our findings shed light on the beneficial effects of phytoncide on cognitive function in MCI.