The limbic sytem, which deals with the regulation of emotions, was once thought of as the rhinencephelon, or “nose-brain,” because it was first studied in rats for whom olfaction (sense of smell) and emotions are utterly entwined. The limbic system is comprised of different subareas, and these subareas send projections into other parts of the brain, especially the hypothalamus, and the connection between the limbic system and the hypothalamus is important for our understanding of aromatherapy.
But first, let’s back up and look at something called the automonic nervous system (ANS). There are all kinds of autonomic (automatic) functions in your body that are vital to keeping you alive and well, and these functions happen involuntarily; you don’t need to consciously control them. And this is a good thing, because we’re talking about functions like the beating of your heart, the amount of sugar you have in your blood, and so forth. You would spend your entire day and then some consumed by these processes if you had to think about them.
Three different layers of the brain have an influence over these autonomic functions, which are carried out by the autonomic nervous system (ANS), and the hypothalamus is the first layer of influence. If you were injured and your blood pressure started dropping, a blood pressure sensor would send a message up the spinal cord to your hypothalamus, and through a few more steps, your blood pressure and heart rate would increase, thereby bringing your body back into balance. Thank you, hypothalamus!
The second layer of influence on autonomic functions is the limbic system, and it is here where we start to see the possible mechanisms for aromatherapy’s powerful effects. A scent or an image can trigger an emotional response in the limbic system, which in turn sends a message to the hypothalamus, and again, the autonomic nervous system (ANS) is activated. It’s like pouring a double cocktail emotions and hormones.
Finally, the third layer of influence on autonomic functions is the cerebral cortex, another part of the brain and one that is involved in memory, learning, complex processing, decision making, and more. In this part of the brain, thought and memory are the triggers that can send messages to the limbic system and to the hypothalamus, again stimulating the ANS.
So, we’ve just looked at three ways that autonomic/involuntary processes in your body can be affected, processes like the beating of your heart, your rate of digestion, and the levels of hormones in your body. These three ways are the hypothalamus, the limbic system, and the cortex. Let’s grossly oversimplify these by relating each one to a key function: the hypothalamus produces hormones, which are powerful chemical messengers; the limbic system deals with emotions; and the cortex handles thoughts and memories.
In other words, the basic, involuntary functioning of our body can be influenced by hormones, emotions, and thoughts and memories. (Of course, it can be affected by other things as well, but these three are important for our purposes.)
Let’s connect this to aromatherapy. If you smell, say, lavender essential oil, your olfactory bulb sends a message to your limbic system, triggering an emotional response, and to your cortex, potentially triggering thoughts and memories (e.g you have a memory of being in the backyard while your grandma hangs lavender-scented laundry on the clothesline). Your limbic system, in turn, can send messages to your hypothalamus, causing hormones to be released, hormones that can have a multitude of effects on your body, such as lowering your heart rate and respiration. Thank to one little scent, you’re having an emotional response, you might be experiencing long-forgotten memories, and your body is likely producing hormones that are traveling throughout your body, causing any number of physiological effects.
This is all well and good, but let’s take it even further and talk about how aromatherapy can even change the expression of your DNA. In a lecture series called Biology and Human Behavior: The Neurological Origins of Individuality, Dr. Robert Sapolsky outlines different ways in which our environment, including scents, can influence the activity of our genes.
In a nutshell, DNA is like the blueprint, or set of instructions, for your cells. However, each strand of DNA contains instructions for all kinds of things, and your cells aren’t using all parts of these instructions at the same time. How does this work? Well, to oversimplify again, imagine that your DNA looks like a string of pearls. After every nine pearls on the string, there’s a blue bead, and this blue bead plays a special role. It’s like a switch that allows a particular stretch of nine pearls to activate. Unless the pearls are activated, they can’t have any effect in the cell; they’re essentially just sitting there doing nothing, so these blue beads are very important. If the blue beads turn the pearls “off,” nothing’s happening, but when the blue beads activate the pearls, things start to happen.
Okay, so what tells the blue beads (known as promoters) to switch on? There are proteins in your cells called transcription factors, and they have the power to flip the switch, turning on the blue beads, and thus allowing your DNA to spring into action. What’s interesting is that these transcription factors can be influenced by things in your external environment, like scents. Dr. Sapolsky gives the example of a male wildebeest who smells a rival male who has been scent marking in his territory. Sound the alarm! The scent of the rival works on the pathways we’ve just discussed and has the ability to turn on sections of the wildebeest’s DNA, perhaps causing a certain neurotransmitter to be produced, which in turn has a powerful effect on the brain, generating, perhaps, an aggressive response in our wildebeest friend: Off he goes, charging across the savannah to exact revenge!
An example that you might be familiar with in humans: Studies have shown that women in regular close contact will begin to sync their ovulatory cycles, typically matching the cycle of the socially dominant female in the group, and olfactory triggers (pheromones) are responsible. If you’ve ever lived in a dorm full of women PMSing at the same time, you know just how powerful this can be.
While many of us have had the experience of being energized by peppermint or soothed by lavender, it’s fun to peel back the layers and explore what’s going on in the brain and in the cells of our body while this is happening. Scents have the power to change our heart rate and other bodily functions, our mood, our thoughts, and the expression of our DNA. Ponder that during your next aromatherapy session!