Effects of inhaled essential oils on central nervous system, autonomic nervous system, emotional states and reaction time: randomized crossover study

Abstract

The odors of essential oils used to cure various symptoms refer to aromatherapy. The effects of inhaled essential oil on humans are therapeutically effective due to both the psychological and physiological effects. A large body of previous studies have been conducted on the effects of essential oil inhalation. However, the studies conducted on the effects on central nervous system and reaction time task are still lacking. Thus, the purpose of this study was to evaluate the effects of selected essential oils including neroli oil (Citrus aurantium Linn.), cinnamon leaf oil (Cinnamomum zeylanicum Blume), and rice paddy herb oil (Limnophila aromatica Merr.) on central nervous system (brain wave activity), autonomic nervous system (heart rate, blood pressure, respiratory rate, skin temperature), emotional states and reaction time. This study was an experimental study with a randomized crossover design. Individuals who volunteered to participate in this study submitted a written consent form before participating in the study. Seventy-two healthy volunteers were recruited from general public and assigned into 3 sessions (24 participants/session) based on these 3 essential oils administered in this study using a simple random sampling method enclosed in envelopes. All the participants received 2 interventions (essential oil and carrier oil) separated by a 1-week washout period. The essential oil and the sweet almond oil were administered while ANS parameters were recorded using BIOM7000 Patient Monitor. Nicolet EEG v32 was used to record brain activities and the self-evaluated questionnaire on emotional states in Thai version of The Geneva Emotion and Odor Scale was used to measure the subjective feelings of the participants. The participants were instructed to rapidly complete the simple and choice reaction tasks on computer screen by the Deary-Liewald reaction time program. Data were analyzed using paired t-test. A value of p < 0.05 was considered statistically significant. After the neroli oil inhalation, the participants felt more relaxed, romantic and less stressed. After the cinnamon leaf oil inhalation, the participants felt more relaxed, calmer and less stressed. After the rice paddy oil inhalation, the participants felt more relaxed. All 3 essential oils had statistically significant attenuated effects on ANS parameters. Neroli essential oil increased theta, and alpha waves as well as decreased beta wave. Cinnamon leaf oil increased alpha wave and decreased beta wave. Rice paddy herb oil decreased theta wave but increased alpha wave. The neroli essential oil and the rice paddy herb oil statistically significantly decreased the time spent on the simple reaction time tasks. The cinnamon leaf oil tended to reduce the time spent on the simple reaction time tasks. All 3 essential oils had no significant effects on correct answers as well as the response times for the choice reaction time tasks. The inhalation of neroli oil, cinnamon leaf oil, and rice paddy herb oil could induce the relaxing effects on autonomic nervous system, positive emotional states and the relaxation of brain state.