Aroma and the Brain

This blog post is the first in a series exploring how aromatherapy and plant extracts holistically affect change and support the health and well-being of body, mind, emotions, and spirit. In this post, I examine our sense of smell, the brain, and how aroma connects with memory, emotions, and stress levels. In following blog articles, I will review clinical studies that examine how the chemical components of plant extracts address physical symptoms, regardless of aroma. I will end the series by coming full circle to illustrate how all of this can be used to support people living with mental, emotional, and spiritual health concerns. I’m excited to give you a glimpse into how aromatherapy combines my passions of nature, science, and holistic healthcare.

Take a Whiff

When we hear the term “aromatherapy,” often the first thing that comes to mind is something we smell. Although smell is only a small part of aromatherapy, I find it to be an important method of addressing patterns of stress and trauma held within the body-mind-spirit system.

The sense of smell and the act of smelling is also called olfaction. It is made possible by two odor-detecting patches high up in our nasal passages called the olfactory epithelium. For humans, these patches contain about 5 to 6 million olfactory receptor neurons—cells that receive odor molecules and translate their messages to our brain. Other mammals have many more of these odor-detecting cells—rabbits have about 100 million olfactory receptor neurons and dogs have about 220 million! However, we can still recognize thousands of different smells and detect them in very small quantities (less than one part odor in several billion parts of air!).2

When we smell an aroma, odor molecules enter our nose as we inhale and bind to the olfactory receptor neurons of the olfactory epithelium. The neuron translates the odor molecule into an electrical impulse and transmits the message to the brain. In the brain, these impulses go to the cerebral cortex, where we process the message to identify the aroma and determine its source, and to the limbic system which controls things like behavior and body functions and is the seat of emotions and long-term memories.1, 3 Smell is the only one of our main senses that connects directly to our limbic system. In fact, the limbic system used to be referred to as the “rhinencephalon,” or “nose brain.” Now, however, this term refers to the structures of olfaction and parts of the limbic system.5

The Emotional Brain

The limbic system consists of a number of brain structures held beneath the folded grey matter of the cerebral cortex. The brain regions that make up the limbic system include the hypothalamus, amygdala, hippocampus, and limbic cortex. These structures regulate many important body functions that influence our health, daily life, and emotions.

The hypothalamus is involved in regulating metabolism, growth, mood, and circadian rhythm, which is our sleep-wake cycle.4,7 The amygdala is involved with our emotional response to smell and our emotional food intake. It also helps us understand social cues and behaviors necessary for social interaction.4 The hypothalamus and amygdala are the main actors in causing the stress response of “fight-flight-freeze” and triggering the release of stress hormones.4 The limbic cortex influences emotional reactions and controls judgement, motivations, and mood.7 The hippocampus is critical to long-term memory storage and retrieval while the amygdala helps to create and retrieve emotional memories.4,7 It is clear that our limbic system is referred to as our “emotional brain” for good reason.

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Smell and the Limbic System

Although the structures and functions of the limbic system are only partially understood, what research has uncovered makes a compelling case for the use of aromas to reduce stress, boost mood, and recover from trauma. Clinical research studies have shown that different aromas effect mood, behavior, and physical function due to their ability to directly affect the nervous system. For instance, exposure to neroli and grapefruit essential oils increased slow alpha and theta brainwave activities, promoting a more calm and relaxed state.6

Some aromas are widely considered to be calming and others are generally accepted to be more stimulating, while some are both depending on the situation and how they are used. However, any aroma may create the opposite effect than studies suggest if it relates to an unhappy or traumatic memory. Countless studies illustrate the various calming aspects of lavender essential oil. However, if the smell of lavender connects someone to an unhappy or traumatic memory, the memory is retrieved by the smell memory and triggers a stress response. Someone else who has a happy memory relating to the aroma of lavender or no memory connecting to it may feel uplifted and calm.

I find that the most important thing to consider when using aromas to support a desired shift in the nervous system, is how each individual relates and reacts to the aroma. Aroma preferences and effects can be as varied as our individual experiences and memories. The direct connection between smell and the limbic system is a wonderful tool for addressing difficult memories, emotions, and our stress response. Even when it’s difficult to find words, beautiful aromas connect deep within and remind us that we are safe, supported, and going to be okay.

References

  1. Battaglia, Salvatore. The Complete Guide to Aromatherapy, 2nd edition. Brisbane, Australia: The International Centre of Holistic Aromatherapy, 2003.
  2. Fox, Kate. “The Smell Report: An overview of facts and finding.” Social Issues Research Centre, www.sirc.org. 2009. Accessed 2 May 2018. http://www.sirc.org/publik/smell.pdf.
  3. Keim, Joni and Ruah Bull. Aromatherapy & Subtle Energy Techniques: Compassionate Healing with Essential Oils, Revised & Updated. Middletown, DE: Self-Published with CreateSpace, 2015.
  4. Rajmohan, V. And E. Mohandes. “The Limbic System.” Indian Journal of Psychiatry, vol. 49, no. 2, Apr-Jun 2007, 132-139. PubMed, doi: 10.4103/0019-5545.33264. Accessed 4 May 2018.
  5. “Rhinencephalon.” ScienceDirect. Accessed 6 May 2018. https://www.sciencedirect.com/topics/neuroscience/rhinencephalon.
  6. Sowndhararajan, Kandhasamy and Songmun Kim. “Influence of Fragrances on Human Psychophysiological Activity: With Special Reference to Human Electroencephalographic Response.” Scientia Pharmaceutica. 2016; vol 84, no. 4, 724-751. MDPI, doi: 10.3390/scipharm84040724.
  7. Swenson, Rand. “Review of Clinical and Functional Neuroscience - Sweson: Chapter 9 - Limbic System.” Dartmouth Medical School. 2006. Accessed 4 May 2018. www.dartmouth.edu/~rswenson/NeuroSci/chapter_9.html.