The Science of Hiking

Harvard physician Paul Dudley White, the ‘father of American cardiology’, believed that a brisk, five mile walk every day is as good a remedy for a restless mind as anything the worlds of medicine and psychology have to offer. Many literary notables, from Charles Dickens to Will Self, have written at length on the restorative effects of their peregrinations through the urban jungle, but as Dr. White well understood, there is something unique about walking in natural surroundings that no amount of urban wandering can approximate.

George Orwell, Thomas De Quincey, Friedrich Nietzsche, Ralph Waldo Emerson, Søren Kierkegaard, Thomas Mann, Vladimir Nabokov, Henry David Thoreau and countless other writers have remarked on the effects of time spent in nature on our intellectual and creative faculties. The physicist Werner Heisenberg was a keen hiker, as were Paul Dirac, Otto Frisch and Lise Meitner, all of whom reported having come to key scientific discoveries while out walking in the hills. For the English Romantics, through whose influence wandering the countryside à pied became a popular leisure pursuit in England in the late 1700s, immersion in nature was not only a source of literary inspiration (in + spirare — ‘to breathe in’), but fundamental to the creative process. William Godwin “made whole books” as he walked. Across the Channel, Jean-Jacques Rousseau, who spent much of his youth wandering the hills of Central Europe, found in the natural world a clarity of thought that eluded him amid the bustle of urban life. “Cities”, Rousseau concluded, were “the abyss of the human species”.

Over the last few decades, the restorative effects of nature — understood intuitively by writers and artists for centuries— have become a key focus of scientific research. With more than 50% of the world’s population now living in cities, interest in the ramifications of our increasing alienation from the natural world has led to a greater understanding of the importance of nature exposure in terms of its impact on our psychological well-being.

A spate of studies have looked in particular at an apparent link between the rapid and widespread urbanisation that has occurred across the world over the last half-century and a marked rise in instances of mental illness over the same period. The exact cause of this correlation is still unknown, but one theory holds that a decline in the amount of contact we have with the natural world may have something to do with it.

This was the hypothesis of a 2015 study led by Gregory Bratman of Stanford University’s Center for Conservation Biology, who sought to establish what exactly it is that might connect reduced contact with nature to the development of psychological disorders. One explanation, Bratman suggests, could be the impact of nature exposure on ‘rumination’, a maladaptive pattern of self-referential thought focused on negative aspects of the self, known to be a risk factor for depression and other forms of mental illness.

Bratman and his colleagues divided a cohort of city-dwellers into two groups, and asked each to take a 90-minute walk — one through a grassy area near the Stanford University campus, the other along a busy main road in Palo Alto. Brain scans conducted on those who walked through the natural setting showed reduced neural activity in the specific area of the brain responsible for self-focused behavioural withdrawal associated with the development of mental illness. Those who walked through the urban setting showed no such effects, leading the authors to conclude that even a brief excursion in verdant surroundings substantially decreases obsessive, negative thoughts.

Bratman’s study follows in a tradition of scholarship rooted in a school of thought known as Attention Restoration Theory (ART). Pioneered in the 1980s by Rachel and Stephen Kaplan in their book The Experience of Nature: A Psychological Perspective, ART suggests that exposure to nature has specific effects on our executive attentional system, which can become worn down due to the demands made of it by urban life.

Permanent background noise, compulsive and increasingly compulsory engagement with technology, the demands of multi-tasking and the necessity of constantly having to respond to sudden, disruptive stimuli place a severe strain on our cognitive functions. By contrast, natural environments are rich in the characteristics necessary for the brain to replenish itself.

This hypothesis has been found to hold true in a slew of studies since the 1980s. A well-known experiment by Terry Hartig and colleagues, for example, comparing the attentional capacity of wilderness vacationers, urban vacationers and non-vacationers before and after their respective holidays, found that the wilderness group showed significant improvements in attentional capacity, measured through proof-reading tests.

In another study, Hartig et al. divided a cohort of participants into three groups, all of which completed attention-depleting tasks and then spent 40 minutes walking in a natural setting, walking in an urban setting, or listening to music and reading magazines. Again, participants in the nature walk group significantly outperformed the others at the proof-reading task, affirming a substantial recovery in directed attention.

Similar studies have found that interactions with nature lead to improved performance on Attention Network Tasks and backwards digit span tests used to assess working memory, the cognitive system responsible for temporary storage and manipulation of information.

Even looking at images of the natural world has been shown to have such effects. This kind of ‘passive’ interaction with nature, as opposed to more active engagement in the form of hiking, was the subject of an oft-cited piece of research by Carolyn Tennessen and Bernadine Cimprich, which found that college students whose dormitories looked out onto more pastoral vistas scored better on a range of attentional measures than those with views of less bucolic landscapes.

Exposure to nature thus seems to be effective in replenishing lower-level modules of the executive attentional system. But there is a growing body of evidence to suggest that it may also have an impact on higher-level tasks, such as creative problem solving.

In a 2012 study, psychologists David L. Strayer and Ruth and Paul Atchley sent a group of participants on a four-day wilderness hike, completely cut off from technology, and subsequently asked them to carry out tasks requiring creative thinking and complex problem solving. The study found that participants’ performance on these tasks improved by 50%, leading the authors to conclude that “[t]here is a real, measurable cognitive advantage to be realized if we spend time truly immersed in a natural setting”.

This improvement of higher-order cognitive skills derives, the authors of the latter study argue, from “an increase in exposure to natural stimuli that are both emotionally positive and low-arousing and a corresponding decrease in exposure to attention demanding technology, which regularly requires that we attend to sudden events, switch amongst tasks, maintain task goals, and inhibit irrelevant actions or cognitions.”

Whereas the stimuli we encounter in nature, as University of Michigan professor Marc Berman explains, “modestly grab attention in a bottom-up fashion, allowing top-down directed-attention abilities a chance to replenish”, urban environments are “filled with stimulation that captures attention dramatically and additionally requires directed attention (e.g., to avoid being hit by a car), making them less restorative.”

The efficacy of exercise per se on cognitive function and emotional wellbeing is well-established, but the full extent of the role of nature exposure in particular, and the mechanisms by which it affects us, is only now beginning to be understood in all its complexity. A walk in the countryside is rich in unique characteristics that will do more for the human brain than any amount of time on a treadmill ever can, and in a rapidly urbanising world, the findings of ongoing research in this field will inevitably have ever more profound and far-reaching implications.

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Image: Krisjanis Mezulis, via Unsplash.