Study on the Effect of Mentha × piperita L. Essential Oil on Electroencephalography upon Stimulation with Different Visual Effects

Abstract

Essential oils have long been used to fight infections and treat various diseases. Peppermint (Mentha × piperita L.) is an herbal medicine that has been widely used in daily life since ancient times, and it has a wide range of applications in food, cosmetics, and medicine. Mint oil is refreshing because of its cool and comfortable smell; therefore, it is often used in ethnopharmacological studies. The present study investigated the effects of peppermint essential oil in electroencephalographic activity response to various visual stimuli. The electroencephalographic changes of participants during peppermint essential oil inhalation under white, red, and blue colour stimulations were recorded. A rapid Fourier transform analysis was used to examine the electroencephalograph power spectra of the various microstates induced by inhaling the oils. Peppermint essential oil had various effects on the brain when subjected to different visual stimuli. Alpha waves increased in the prefrontal area in the white-sniffing group, which facilitated learning and thinking. In the blue-sniffing group, the changes were less pronounced than those in the red group, and the increased alpha wave activity in the occipital area was more controlled, indicating that the participants' visual function increased in this state. Based on EEG investigations, this is the first study to indicate that vision influences the effects of peppermint essential oils. Hence, the results of this study support the use of essential oils in a broader context to serve as a resource for future studies on the effects of different types of essential oils.

Keywords: colour; electroencephalograph; inhalation; peppermint essential oil.

Figure 1

EEG spectral spectrograms before and after inhalation of EOs. Using FFT in EEGLAB software, the brain activity of 20 subjects in the same microstate was summarised as a spectrogram. (A) White without PEO. (B) White with PEO. (C) Red without PEO. (D) Red with PEO. (E) Blue without PEO. (F) Blue with PEO. Significant changes occurred in each region during the inhalation of EOs.

Figure 2

Single-channel analysis comparison graph for each group, comparing bands of the same channel in the same colour with or without PEO inhalation. (A,D,G,J) are white groups, (B,E,H,K) are red groups, and (C,F,I,L) are blue groups (p-values: * < 0.05, ** < 0.001, *** < 0.0001. Relevant data can be found in supplementary materials.).

Figure 3

Alpha and beta wave activity under six states. The six different states, defined as microstates 1 to 6, are white, white with PEO, red, red with PEO, blue, and blue with PEO, respectively. (A) Significant differences in alpha band. (B) Significant differences in beta band. In the same group, values followed by different letters were significantly different (p < 0.05).

Figure 4

Experimental flow chart ((A) Experimental process. (B) Potential distribution).