Effect of olfactory stimulation of isomeric aroma compounds, (+)-limonene and terpinolene on human electroencephalographic activity

Introduction: The present study was undertaken to evaluate the olfactory stimulation of (+)-limonene and terpinolene on human electroencephalographic (EEG) activity in order to understand their action on brain function by isomer compounds. Methods: The effect of inhalation of isomers on EEG activity was evaluated by the measurement of EEG power spectrum in 18 healthy participants. EEGs were recorded using QEEG-8 system from 8 grounding electrodes according to the International 10-20 System. Results: The results indicated that the relative high beta (RHB) activity increased significantly in the right temporal region (from 0.1250 to 0.1429 mu V, p < 0.05) during the inhalation of (+)-limonene. Whereas, the relative mid beta (RMB) activity decreased significantly (from 0.0646 to 0.0561 mu V, p < 0.05) and the relative fast alpha (RFA) activity increased significantly in the right prefrontal region (from 5.6215 to 7.3336 mu V, p < 0.05) during the inhalation of terpinolene. According to gender variation, significant changes of absolute and relative beta activities were observed in men than women during the inhalation of both the compounds. Women responded well to both the compounds by a significant increase of absolute fast alpha activity. When compared with (+)-limonene, terpinolene exhibited positive effect by reducing the tension and increasing the relaxation and stabilization states of brain function. Conclusion: The isomers produce different states of brain function as affect the different regions of brain. Further, the EEG activity of isomers on human brain is highly related to the structural arrangement of individual compounds and gender difference. (C) 2015 Elsevier GmbH. All rights reserved.