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54 m a s s a g e & b o d y wo r k n ove m b e r/d e ce m b e r 2 0 2 1 MECHANISMS THAT CAUSE PSYCHOLOGICAL EFFECTS Essential oils help us achieve psychological session goals through olfaction (the sense of smell), and the aromas' effects on the central nervous system, 1 their influence on the amygdala, 2 their ability to change brain chemistry, 3 and their euphoric properties. 4 Other psychological effects of essential oils exist, but here we'll focus on these primary mechanisms, understanding that psychological effects are often overlapping and complex. Olfaction When you inhale the aroma of your coffee, crush a sage leaf between your fingers to cook, or smell lilac blossoms in the spring, you are experiencing the earliest sense. Before our single-celled ancient ancestors could see, hear, or touch, they could smell. At the top of each inner nasal cavity is a patch of mucus-covered tissue called the olfactory epithelium. Odor molecules dissolve into the olfactory epithelium when we inhale or pass through the throat when the tongue pushes air to the back of the nasal cavity when we chew or swallow. Though only a few centimeters wide, the olfactory epithelium contains more than 100 million olfactory receptor cells. 5 We literally dangle exposed nerve endings into the vast ocean of air eddying inside our nasal cavities and fish for aroma information as smells drift by on air currents. Each olfactory receptor has a different shape that allows it to grab hold of a particular type of aroma. 6 One receptor hooks spicy aromas while piney aromas float free. Another receptor hooks flowers and vanilla. Others, coordinating their findings, net the complicated chemical odorants that compose the aroma of your massage lubricant. There are approximately 400–450 different olfactory receptors that allow us to differentiate between approximately 1 trillion different odorants. 7 The Limbic System Neurons from olfactory receptors bundle together to form the olfactory nerve, which travels to the olfactory bulb (the main organ of smell). From the olfactory bulb at the base of the brain, signals travel to the limbic system triggering olfactory responses. The limbic system is a group of brain structures responsible for adrenaline flow, emotion, behavior, motivation, long-term memory, and olfaction. 8 The amygdala, as part of the limbic system, is the integration center for emotions, emotional behavior, and motivation. It is responsible for recognizing the emotional significance of events in the external world and supporting an appropriate behavioral response. The hypothalamus links the nervous system to the endocrine system through the pituitary gland. It triggers parts of the endocrine system to start or stop producing certain hormones. Aromas trigger olfactory responses in these brain structures. For example, since early times, the smell of fire alerts us to potential danger and triggers the fight- or-flight response. Likewise, the variation in the aroma of a particular food item lets us know it's rotten and we shouldn't eat it. Synchronized menstruation in women is caused by an olfactory response, as are physiological changes and behaviors that arise from pheromonal cues. Pheromones are chemical factors that trigger a social response in members of the same species. OLFACTION: Through an olfactory response, essential oils influence the central nervous system, amygdala, brain chemistry, and sense of emotional equilibrium. Courtesy of Spa Bodywork, 3rd Edition.