The Oldest Part of the Brain

The oldest part of the human brain, the limbic system, is known as the “smell brain’, and it is also associated with the processing of emotions, memories, arousal, and learning. Essentially, our olfactory system is essential to our existence. Smell provides a vital survival function and bypasses our ‘thinking’ brain: If we smell something which is putrid or rotting, we have an automatic physical reaction – we are repelled by it to avoid a dangerous or unhealthy situation.

The sense of smell is also able to affect us in other ways. Smell, at a sub-conscious level, can influence our choice of sexual partner, bonding between mother and child, elicit immediate remembering (and the uncovering of forgotten memories) and the promotion of relaxed states of mind.

Across a range of scientific studies, the olfactory system has been linked with a number of health benefits such as decreased anxiety, healthier metabolism, clearer thinking, better mood and alleviating autoimmune conditions. As a complimentary treatment alongside medical interventions, the use of scents has helped mitigate the effects of neurological disorders, such as in patients with Alzheimer’s disease. It has been found, for instance, that there is a positive correlation between nostalgic memories triggered by smell and positive emotions, self-esteem, optimism, social connectedness, and meaning in life (Reid, et al., 2015, Scent-evoked nostalgia. Memory, 23, 157-166) which are important factors to promote in those with Alzheimer’s.

Campfires, freshly mown grass, and rain often feature in people’s reports of nostalgic scents that calm the mind and produce a sense of wellbeing. Certainly, not having a working sense of smell (‘anosmia’) can have a negative effect on quality of life and emotional wellbeing, evidenced by those people who lost their sense of taste and smell after contracting COVID.

In particular, plants have formed a significant part in human well-being and survival throughout evolutionary history. Some herbs and spices have been known for thousands of years as having medicinal properties. These plants, in various forms (e.g., bark, leaves, seeds, flowers, oils, teas, smoke, etc.) can be applied to the skin, ingested, and inhaled to have the desired curative effects. Smelling plum blossom and geraniums, for example, can positively affect people’s psychological and physiological states (Bentley, et al. 2023, Nature, smells, and human wellbeing, Ambio, 52, 1–14)

Moreover, resinous and aromatic woody plants such as trees and shrubs have been connected to spiritual health and practices. So, alongside the more western understanding of the biological effects, the eastern view would also acknowledge the more subtle energetic (‘Tantric’) effects of such plants on the human condition. The burning of sandalwood as one example, has been in use for at least 2,500 years within several eastern religious and cultural practices. Sandalwood oil is recognised as having purification properties (when mixed with other oils) and can be applied in a range of ways such as an antidepressant, alleviating acne, eczema, insomnia, anxiety and maintaining skin health. In Islamic beliefs, sandalwood incense is laid at the feet of the dead in order to carry their souls to heaven. 

Written by Dr Joe Hinds (MSc, PG Dip, DPhil) on behalf of Menteath

Author of Ecotherapy: Theory, Research and Practice 

Buy Book here

In this thought-provoking book, Jordan and Hinds provide a comprehensive exploration of this emerging area of practice. Divided into three parts, the book offers a unique examination of a range of theoretical perspectives, unpacks the latest research and provides a wealth of illuminating practice examples, with a number of chapters dedicated to authors' own first-hand experiences of the positive psychological effects of having contact with nature.