Effects of Phytoncide Inhalation on Stroop Task Performance in Patients with Mild Cognitive Impairment: An fNIRS Pilot Study
Seungchan Park1,*, Jiheon Kim1,2,*, Hansol Kim1, Do Hoon Kim1,2
1Mind-Neuromodulation Laboratory, College of Medicine, Hallym University, Chuncheon, Korea
2Department of Psychiatry, Hallym University Chuncheon Sacred Heart Hospital, Chuncheon, Korea
Correspondence to: Do Hoon Kim
Department of Psychiatry, Hallym University Chuncheon Sacred Heart Hospital, 77 Sakju-ro, Chuncheon 24253, Korea
E-mail: dhkim0824@gmail.com
ORCID: https://orcid.org/0000-0002-6588-9221

*These authors contributed equally to this study.
†The research findings were presented in poster format at the CTAD (Clinical Trials on Alzheimer’s disease) 2023 conference held at Boston Park Plaza from October 24 to 27, 2023, highlighting the key findings and methodology.
Received: January 2, 2024; Revised: February 13, 2024; Accepted: February 14, 2024; Published online: March 15, 2024.
© The Korean College of Neuropsychopharmacology. All rights reserved.

This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
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 W = 18.50, p = 0.385) or hemodynamic response, a significant increase in Stroop task performance (Wilcoxon W = 1.50, p = 0.009) and hemodynamic attenuation in the left VLPFC (Wilcoxon W = 56.00, p = 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.
Keywords: Phytoncide; Mild cognitive impairment; Dementia; Stroop test; Functional near-infrared spectroscopy

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