Scent provides an often random access to the brain and to the molecules, cells and circuits involved in pain processing. The first Cranial Nerve, the olfactory nerve, provides a way to smell the environment, allowing our brains to react with disgust, pleasure, revulsion, attraction, hunger and memory activation. The olfactory nerve is the only cranial nerve that starts outside of the brain. It’s origins are in the upper 1/3 of the mucous membranes in the nose, quickly entering the cranium through a series of holes at the top of the nasal bones, called the cribiform plate. The first synapse of the scent circuit in the brain occurs in the olfactory bulb and the second is in the amygdala, traveling to the insula, ventral medial prefrontal cortex, anterior cingulate cortex, posterior cingulate cortex and posterior parietal cortex. Hence, scent is perceived in part of the same circuit we experience pain and pleasure, establishing the importance of scent for basic survival, with avoidance of scents that provoke disgust and pursuit of those that give pleasure. Human beings are capable of distinguishing 300 to 400 distinct scents, and combinations of them allows us to determine thousands of specific odors.
When scents are purposefully used the brain can be accessed for specific effects. This is the basis of aroma therapy. Ironically, this is often dismissed by mainstream medicine, despite some excellent research in this area regarding effects of many naturally occurring scents. These can be soothing and stimulating, invoking a sense of well-being and happiness. The brain releases substances that produce pleasure, including GABA, endorphins, oxytocin, anandamide and adenosine. These brain neurotransmitters oppose those in the equivalent pain circuits, Glutamate, Substance-P, Calcitonin Gene Related Peptide, Adenosine Triphosphate.
One scent in particular, peppermint, blocks the main pain neurotransmitter, Substance-P at presynaptic release sites, while also blocking calcium in post-synaptic calcium channels. Since the amygdala is the second synapse in the scent circuit and the first synapse in perceived pain, the activity of peppermint blocking Substance P and calcium channels theoretically makes it a potential pain reliever. Substance-P is a very specific neurotransmitter dedicated to five known effects, pain, nausea, anxiety, depression and inflammation. There is some evidence of peppermint’s effectiveness with irritable bowel and local burning skin pain. Peppermint tea is used for it’s soothing and calming effects, and most people have positive memories associated with its scent and taste. Additionally, peppermint has long been used in hospital wards to cover harsh scents to help with urinary hesitancy.
Over the last several years we have conducted a large case series in conjunction with aromatherapist, Sharon Thom, MA, MS, using a proprietary blend of peppermint and several other compatible scents. Results have been positive for pain relief, decreased nausea and stress reduction. Future studies will include a prospective trial of pain relief using peppermint oil blend, pain scales and functional imaging.