Do you know that our olfactory function (the sense of smell) may affect our brain health?
There is evidence of the existence of a complex connection between the olfactory system, the central nervous system (CNS) and our cognitive behaviour.
In fact, various studies showed associations between the loss of olfactory function and CNS-related diseases including depression, schizophrenia, Alzheimer’s (AD) or Parkinson’s diseases.
In some of these pathologies, olfactory dysfunctions precede the disease symptoms and are considered as a predictive factor.
For example, 2018 Meta Analysis showed that olfactory dysfunction is one of the earliest, preclinical symptoms observed in AD. It worsens progressively as patients progress from mild cognitive impairment to AD.
In a recent experiment, published a few weeks ago in Frontiers in Immunology, researchers discovered that inhaling menthol can improve cognitive abilities in animal models of Alzheimer's, possibly by modulating the immune system.
Researchers found that the smell of menthol reduced the level of interleukin-1-beta (IL-1b), a protein crucial to the inflammatory response. By inhibiting this protein with a specific drug, cognitive abilities were also improved in mice experiments.
These data suggest an association between the immunomodulatory capacity of smells and their impact on the cognitive functions of the animals, highlighting the potential of odours and immunomodulators as therapeutic agents for CNS-related diseases.
But it’s an animal model. The methanol inhalation might work for mice, but not necessarily for humans.
Let’s explore the topic of therapeutic use of certain smells in managing stress or even depressive symptoms.
Several studies have shown that the effects of various fragrances on mood, physiology and behaviour are due to the fragrance’s direct and intrinsic ability to interact and affect the central nervous system.
To analyse it, researchers used an electroencephalogram (EEG) test to measure different types of waves in the brain.
But first let's look at the differences between various brain waves and their functions.
There are different types of electrical signals in the brain, called alpha, beta, gamma, delta and theta waves. Brain waves naturally appear during both the active and resting states.
Our thoughts, emotions and behaviour are the reflection of neuronal activity within the brain.
The brain waves with slower frequencies are dominant when we feel tired, slow, or dreamy.
On the other hand, the higher frequencies are dominant when we feel wired or hyper-alert.
The following categories of frequency bands are the most therapeutically relevant.
Results of EEG studies are quite interesting.
Essential oil of Mentha arvensis or mint seems to reduce mental stress. EEG showed a relative increase in fast alpha waves and 90% reduced frequency in gamma waves.
Klemm et al. reported that the odours of birch tar, jasmine, lavender and lemon significantly increased the theta activity.
Inhaling lavender oil caused significant decreases of blood pressure, heart rate, and skin temperature, which indicated a decrease of autonomic arousal. In terms of mood responses, the subjects in the lavender oil group categorised themselves as more active, fresher relaxed than subjects just inhaling base oil.
In addition, Schulz et al. investigated the acute sedative effects of eight different plant extracts such as Valeriana officinalis, Lavandula off., Passiflora incarnata, Piper methysticum, Melissa off., Eschscbolzia californica, Hypericum perforatum and Ginkgo biloba. Among the different plant extracts, valerian extract significantly increased delta and theta activities and also decreased beta activity.
Kawakami et al. investigated the influence of fragrances with sedative effects (lemon, lavender and sandalwood) and awakening effects (jasmine, ylang-ylang, rose and peppermint) on visual display terminal task (VDT) activities. The results revealed that fragrances affected the subject's concentration on work and mentally stabilised them when compared with no fragrance control.
Lavender and rosemary were also associated with less depressed affect.
Kawakami et al. investigated the influence of fragrances with sedative effects (lemon, lavender and sandalwood) and awakening effects (jasmine, ylang-ylang, rose and peppermint) on visual display terminal task (VDT) activities. The results revealed that fragrances affected the subject's concentration on work and mentally stabilised them when compared with no fragrance control.
Our olfactory function has a much broader function than we expect. It doesn’t just affect our emotional and mental health, but according to recent research it may be used in future as a biomarker for certain neurodegenerative diseases, such as AD, multiple sclerosis, Parkinson’s disease or amyotrophic lateral sclerosis.
In any case, we should not ignore aromatherapy as a tool to alter our mental state. And I would encourage everyone to explore different odours such as lavender, bergamot or mint in stress management techniques.
Keep in mind, the science is strongly supporting it.