Relaxation Effects of Essential Oils Are Explained by Their Interactions with Human Brain Neurotransmitter Receptors and Electroencephalography Rhythms

Inhaled essential oils (EOs) are bioavailable to the brain and are consistently reported to promote relaxation effects. Their mechanisms of action are however not well understood. The aim of this investigation was to assess the neuroactivity of EOs based on their (i) binding interactions to neurotransmitter receptors and (ii) bioelectrical activities in the brain as measured by electroencephalography (EEG). These EO properties were compared to those of reference pharmaceutical compounds with effects also measured by EEG. Relative receptor binding efficacies of 10 reference compounds, 180 EOs, and 9 EO extracts with 7 different neurotransmitter receptors were calculated using in silico molecular docking procedures. Changes in brain EEG rhythms, as standardized changes in absolute power, were determined for the reference compounds and selected EOs and compared to receptor binding efficacy results. The reference compounds had diverse receptor binding patterns, with EEG responses dominated by EEG-delta wave frequencies. In contrast, the receptor binding pattern of the EOs was remarkably consistent and replicated a subclinical affinity pattern corresponding to the inhibitory glycine-alpha-GLRA3 and dopamine-D2 receptors, producing responses dominated by EEG-alpha wave frequencies. The results support the hypothesis that EOs stimulate neuroactivity by modulating patterns of neurotransmission affecting alpha wave EEG responses.