INFLUENCE OF ODOR STIMULATION ON THE ACTIVATION OF THE CENTRAL NERVOUS SYSTEM

—Analysis with Near-infrared Spectroscopy (NIRS)—

Abstract

Aromatherapy is the well-known practice of using natural oils extracted from flowers, bark, stems and other part of plant, which are called essential oils, to enhance psychological and physical well-being. Aromatherapy is also accepted to be a form of alternative medicine and it is used for the treatment or prevention of diseases, such as pain, depression and anxiety. It is generally believed that essential oils are absorbed via the airway mucosa and the skin, where they travel through the bloodstream and can promote whole-body healing. Although the effect of essential oils on the peripheral nervous system has been well documented, the influence of essential oils on brain functions is not well understood. Therefore, in the present study, we examined the influence of odor stimulation on brain function, as assessed by measuring oxyhemoglobin (HbO₂) levels in the frontal cortex by using near-infrared spectroscopy (NIRS). The subjects (10 females, 9 males) were recruited in Showa University School of Nursing and Rehabilitation Sciences. The odors used were linalool, limonene, benzyl acetate and vanillin, which were diluted with 100% ethyl alcohol at a final concentration of 1.0%. The subjects were exposed to these odors for 30 seconds. Stimulation by linalool and limonene caused a significant increase in HbO₂ levels in the frontal cortex. On the other hand, benzyl acetate and vanillin scarcely affected HbO₂ levels in the frontal cortex. The present results strongly suggest that it is necessary to carefully choose the type of odor, when performing aromatherapy for the purpose of cerebral activation.