Odor-induced modulation of electroencephalogram waves in healthy controls

Abstract

Background: It has been found in some of the electrophysiological studies that odor does affect the rhythm of brain waves. However, there is a lot of inconsistency in terms of the reported findings. Some have reported an increase in alpha activity, whereas others observed increase in theta activity and no change in alpha. Aims and Objectives: The purpose of this study is to observe what changes occur in electroencephalogram (EEG) in healthy participants on administration of two types of odor (lavender and peppermint). Materials and Methods: This study was conducted on 25 healthy, right-handed male and female volunteers. Baseline EEG for 20 min was recorded, followed by test recording for 9 min comprising inhalation of odor 1 (lavender) for 3 min, no odor (for 3 min), and odor 2 (peppermint) for 3 min. Odors were administered through an odor delivery system, which comprised an inlet and outlet rubber tubes connected to a container for placing odoriferous substance. Results: EEG was inspected qualitatively for abnormalities in prominent locations and hemisphere. Both the odors elicited significant EEG abnormalities when compared to baseline recording, which served as control. Odor 1 and 2 both elicited diffuse slowing, focal slowing, and sharp waves mainly in temporal region and partly in centro-parietal and frontotemporal region, with more right hemispherical involvement, and increased theta rhythm. Odor 2 also produced left hemisphere dominant asymmetry. Conclusions: Both lavender and peppermint odor inhalation produces EEG abnormalities which are transient, predominantly affect right hemisphere, and temporal region. Lavender has relatively more relaxing effect on brain compared to peppermint.