Every aspect of Mother Nature is meant for nurturing lives on planet Earth. Besides breathing, through the five senses of our physical bodies, we are continuously nurtured by Mother Nature. Scientists worldwide are discovering these aspects to remind us how ignorantly we are taking Mother Nature for granted.
There has been a consensus that being in nature enables us to experience good physical and mental health for many years now. Previous research from different fields has demonstrated how being in touch with Mother Nature can heal us and boost our immune system. Research has shown that viewing natural scenes can lower heart rate and restore focus, both of which are important for combatting physical and mental health disorders.
An ecologist at the Swedish University of Agricultural Sciences, Marcus Hedblom, recently conducted a virtual reality experiment with his team. According to Hedblom, most of the existing studies on nature and health are based on self-evaluations where participants describe their subjective view of being in nature and how it made them feel. He and his colleagues wanted to identify the physiological mechanisms, and perhaps even the specific sensory stimuli, that could drive stress reduction in natural environments.
Based on a previous study that found that listening to clips of multiple bird species singing in an urban area had a stronger positive effect on people’s perception of the space than listening to one species alone, Hedblom and his colleagues hypothesized that an environment with rich biodiversity would reduce stress faster than a non-natural environment.
To rectify the hypothesis, Hedblom and his colleagues arranged a study where they have recruited 154 study participants and made them experience one of three virtual environments. These environments are— a city, a park, or a Forest. The city scene featured buildings, the sound of traffic, and the smell of diesel, tar, and gunpowder from a roadbuilding ingredient. In the virtual park, there were Trees and buildings, a single bird species—the willow warbler (Phylloscopus trochilus)—and the smell of grass, while the Forest had a complex structure of Trees, shrubs, and deadwood, along with the sounds of nine species of bird and a mixture of mushroom and fir scents.
The team showed the participants visual scenes with the virtual reality headset, had them wear earphones to hear the scenescapes’ sounds, and pumped the odours directly into the individuals’ nostrils via Teflon tubing and custom-made nose pieces. Each person was asked to rate how pleasant they found each of these stimuli on a scale from 1 to 100.
During the experiment, the researchers administered a small electric shock to stimulate a moderate physiological stress response, detectable as a slight rise in the level of the electrical conductance of the participants’ skin. The research team then tracked how quickly participants’ skin conductance levels rose and fell in each of the three environments to determine which was best at reducing stress.
Findings of the study
Right after the shock, participants’ skin conductance in the virtual park or Forest did not increase as much as that of people in the cityscape. And, as the researchers expected, the Forest and the park led to faster stress reduction after a shock than the city scene. But there wasn’t much difference in stress recovery between participants in the virtual Forest versus those in the park, which Hedblom found slightly surprising, given the importance of environmental diversity in the earlier study. He and his colleagues want to investigate the discrepancy further.
Even more intriguing, he says, was the result that the rated pleasantness of smells was the strongest predictor of stress—with high pleasantness being associated with lower initial physiological stress responses and faster recovery—suggesting that smells might have a much more profound effect on reducing stress compared with sights and sounds.
According to Johan Lundström, the co-author of the study, a neuropsychologist at Karolinska Institute in Sweden, the smell is an intriguing sense because of its wiring in the brain. He explained that our sense of smell is unique among other senses because, like other senses, it is the only sense that does not process first by the brain’s switchboard—the thalamus. Instead, the smell signal is sent straight to the hypothalamus, a brain region involved in stress responses, in addition to the olfactory cortex, where odours are processed and perceived.
The signal is relayed from the olfactory cortex to the amygdala, the brain region that detects threats, and to the hippocampus, which is responsible for forming and recalling memories. Bypassing the thalamus means that the hypothalamus, hippocampus, and amygdala can respond faster to smells than they do to other sensory inputs.
Such direct wiring, specifically to the hypothalamus, has led researchers to suspect that smell might regulate stress. But past studies that have tried to measure the impact of odour on stress have not used control odours or other sensory stimuli and therefore haven’t been able to determine if natural scents induce a general pleasant feeling during the experiment that then helps to reduce stress or if the odour itself directly drives the reduction.
This new study indicates that there is at least some direct stress-reducing effect from nature. The authors mentioned that, though the visual and auditory stimuli in natural environments got generally higher pleasantness ratings from participants than odour stimuli did, the natural odour stimuli had the greatest impact on physiological stress reduction.
Other experts like Gretchen Daily, an ecologist at Stanford University, who especially studies green spaces but was not involved in this study, said that the mechanisms by which natural smells regulate stress are still not clear. Some research suggests that certain Plant chemicals might influence stress hormone regulation via the immune system, and so could be important to consider in the design of green spaces. According to her, it is hard to say, and nobody still knows yet what mix of active ingredients is important for these spaces.
- Hedblom, M., et al. (2014). Bird song diversity influences young people’s appreciation of urban landscapes. Urban Forestry & Urban Greening, [online] Volume, 13(3), p. 469-474. Available at: https://doi.org/10.1016/j.ufug.2014.04.002 [Accessed 23rd August 2021].
- Hedblom, M., Gunnarsson, B., Iravani, B. et al. (2019). Reduction of physiological stress by urban green space in a multisensory virtual experiment. Scientific Reports, [online] Volume, 9, p. 10113. Available at: https://doi.org/10.1038/s41598-019-46099-7 [Accessed 23rd August 2021].
- Kaplan, S., et al. (2017). Directed Attention as a Common Resource for Executive Functioning and Self-Regulation. Perspective on Psychological Science, [online] Volume, 5(1), p. 43-57. Available at: https://doi.org/10.1177%2F1745691609356784 [Accessed 23rd August 2021].
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