Reference
McDonnell AS, Strayer DL. Immersion in nature enhances neural indices of executive attention. Sci Rep. 2024;14(1845):1-33.
Study Objective
To measure the impact of nature and urban walks on cognitive attention and mental restoration using neurophysiological and behavioral assessments
Key Takeaway
Walking in natural settings can significantly improve measures of cognitive executive function and attention and can potentially be used as adjunctive therapy for mental health conditions such as attention deficit hyperactivity disorder (ADHD), depression, anxiety, and autism spectrum disorder.
Design
Randomized controlled trial. Based on the type of intervention, it is not possible to “blind” participants or researchers regarding group selection in this study.
Participants
Participants were recruited from the student body and surrounding community of the University of Utah (N=92; mean age 29.4 years; and 71 female, 20 male, 1 gender nonbinary). Eighty percent identified as White/Caucasian, 10% Asian, 7% Latinx/Hispanic, and 3% Black.
Intervention
A 40-minute walk in either a nature- or urban-based setting, both adjacent to the study facility. Each walk was approximately 2 miles and of comparable minimal elevation gain, as well as with comparable environmental factors (eg, temperature, humidity, time of day). Walks were performed alone to minimize social distraction and interaction effects, and participants were required to leave all electronic/digital devices with study personnel until the completion of the study.
Prior to the walk, each participant engaged in a commonly used cognitively depleting task (ie, the Digit Span Backward, counting sequentially down from 1,000 by 7) to induce mental fatigue, as verified by a brief survey prior to data collection.
Study Parameters Assessed
Simultaneous measurement of 3 components of attention (alertness, orientation, and executive function) using electroencephalography (EEG) and the Attention Network Test (ANT), a computer-based reaction-time test. Both measures were collected pre- and post-walk.
In addition, the Perceived Restorativeness Scale (PRS) assessed participants’ subjective experience of the experimental settings.
Primary Outcome
Differences in neural function between those who walked in nature and those who walked in an urban setting.
Key Findings
Walking in nature (vs an urban setting) significantly improved cognitive executive function as measured by EEG: χ2(1)=4.47, P=0.034;
β=2.39, SE=1.13, df=79.20, t=2.12, P=0.0368, 95% CI [0.18 4.59], and Cohen’s d=0.41.
Walking in either setting improved alertness as measured by both EEG (β=0.62, SE=0.25, df=90.75, t=2.51, P=0.0138, 95% CI [0.13 1.10], Cohen’s d=0.28) and ANT (β=12.39, SE=2.00, df=88.48, t=6.19, P<0.001, 95% CI [8.43 16.31], Cohen’s d=0.64).
PRS score was significantly associated with EEG improvement (β=−0.61, SE=0.27, t=− 2.29, P=0.0247, 95% CI [−1.15 −0.080], Cohen’s d=− 0.12, regardless of walk setting).
Transparency
The authors declared no competing interests.
Practice Implications & Limitations
We live in an urbanizing world. Since 2010, more than half of the Earth’s population has resided in cities, and this number is projected to increase to 70% by the year 2050.1 Urban living provides many positive benefits of cultural amenities and access to economic, healthcare, and social services. However, urbanization also has multiple negative health effects resulting from pollution (both air and light pollution), overcrowding, noise, fear, and overstimulation.2 Specifically, these aspects of “urban stress” have been shown to contribute to psychoneuropathologies,3 including the increased urban prevalence of depression, anxiety, and schizophrenia, which cannot be explained just by the relocation of individuals to urban areas that provide greater cultural and healthcare services.4 Functional magnetic resonance imaging (fMRI) studies show urban childhoods result in structural and functional brain changes (compared to rural children) related to mood, attention, memory, and behavior disorders.5,6
In contrast, time spent in nature has the opposite effect. Walking in a forest or sitting in a quiet urban park produces positive changes in both measurable brain function and experienced mental health. Decades of research has demonstrated the benefits of nature time on cognitive, behavioral, and emotional disorders.7 People often report feeling better and thinking clearer. Studies have shown that the presence of green foliage, both outdoor and indoor, improves student academic performance, worker productivity, and error rates.8–10
The explanation for these mental benefits, described in the 1990s by Stephen and Rachel Kaplan via their Attention Restoration Theory(ART), relates to how the brain processes sensory information.11 Typically, we unconsciously filter out a large portion of encountered sensory stimuli, so that our conscious mind can function without being overwhelmed. This filtering process requires varying amounts of “mental effort” depending on the type and source of the stimuli. ART suggests natural environments and features have a positive “restorative” effect on these processes, especially when compared with more distracting and mentally fatiguing urban stimuli. Experiencing a shady woodland stream takes less mental effort to process than noisy city rush-hour traffic, allowing us use more mental energy for other cognitive processes. Thirty years of research has repeatedly demonstrated the validity of ART. 12,13
The current study pairs EEG findings with psychometric data to determine that executive function (EF) is the most relevant aspect of attentional processing regarding natural vs urban effects. The high-level influence of EF affects mental inhibition, behavioral control, working memory, and emotional regulation.14 It has been known for many years using ANT and other similar measures that EF is improved by time in nature via the mechanisms of ART.15 Pairing ANT with EEG here allows McDonnell and Strayer to establish EF as the most important component of cognitive processing affected by natural vs urban settings.
The current study pairs EEG findings with psychometric data to determine that executive function (EF) is the most relevant aspect of attentional processing regarding natural vs urban effects.
These results have implications for a variety of cognitive and behavioral health conditions. Individuals with ADHD have (by definition) a decreased capacity to establish and maintain attention and other EF functions. These individuals can use the EF-restoring capacity of time in nature to enhance attention and improve planning, organization, and focus. Twenty years of research provides evidence that nature time does improve ADHD symptoms,16–18 though not all studies support this.19
Other health conditions related to EF, such as autism spectrum disorders, various mood and anxiety disorders, dementias, and behavioral/conduct disorders, could also benefit from nature-based interventions. While there is ample evidence all of these conditions do benefit from time in nature,20–23 EF was not the primary mechanism of action investigated in many of these studies. Instead, these studies have tended to examine other theories, such as the more psychophysiological stress recovery theory” (SRT), rather than the neurocognitive ART. Efforts are being made to combine these competing and complementary theories.24 Regardless of the mechanism, evidence solidly supports inclusion of nature time as a simple and effective broad-reaching therapy.
This was a well-designed and well-written study with a few very minor limitations. No pre-post measurements were made for the initial pre-intervention stressor task or for the postwalk PRS, so technically these results cannot be included in causality statements. But they are not the primary study outcome measures, so the distinction is minimal. Also, participants walked 3 loops of the nature setting but only 2 of the urban. Conceivably, there could be a greater familiarity with the nature setting that contributed to study results, but it shouldn’t be anticipated this would make much of a difference.
This study adds to the understanding of how time in nature benefits human mental well-being and could prompt physicians and mental health professionals, especially those working with executive-dysfunction patients, to include a walk in nature as part of the therapeutic treatment plan.
