Exposure to nature promotes a state of relaxed alertness, improved attentional processing, and optimal cognitive resource allocation for children and adolescentsAn established body of research indicates that contact with nature can influence children’s mental and physical health, and support beneficial cognitive, emotional, and learning outcomes. Less is understood, however, about the impact of nature exposure on children’s nervous systems. This systematic review aimed to address this gap by synthesizing the findings of all empirical studies that examined the impact of nature exposure on the brain and the peripheral nervous system in children and youth. As the first systematic review to investigate the neurophysiological outcomes that are associated with nature exposure that specifically focuses on children and youth, the study aimed to provide important insights into (1) how nature influences the nervous system and (2) how this evidence can inform nature-based learning (NBL) educational approaches.
A systematic search of the literature was conducted using the Children & Nature Network Research Library and several academic databases using keywords related to both neuroscience and nature. Only peer-reviewed studies of neurotypical children or youth (age 25 or younger) that were focused on measuring the impacts of nature exposure on the nervous system through brain imaging methods or an assessment of the peripheral nervous system’s activity were eligible for inclusion in the review. Studies that examined a broad range of types of experimental nature exposures were eligible, including indoor plants, window views of nature, nature images and videos, and actual outdoor experiences. No limitations were placed on the studies’ publication date or location; however, only studies published in English were considered for inclusion. Twenty-six empirical studies met these criteria and were included in the review. The studies were mainly conducted in Japan (n = 7) and China (n = 4), and to a lesser extent Europe (n = 5; Spain, Germany, the Netherlands, Italy), Taiwan (n = 3), Korea (n = 3), the U.S. (n = 2), Singapore (n = 1), and Australia (n = 1). Nineteen studies were conducted with young adults, six studies with elementary-aged children, and one study with high school students. The studies employed a variety of research designs to examine a range of interventions and forms of nature exposure. Seventeen studies used a within-subjects research design, six studies used a between-subjects design with participants randomly assigned to experimental conditions, and three studies used a longitudinal design. The methodological quality of the studies was assessed with a modified version of the McMaster Critical Review Form for Quantitative Studies. Findings were analyzed and interpreted using the Attention Restoration Theory (ART) and Stress Reduction Theory (SRT) as theoretical frameworks.
Findings were reported according to the studies’ research design which included: (1) <em>brain structure studies </em>(examined relationships between residential greenery and brain structure)<em>, </em>(2) <em>nature exposure-only studies </em>(participants observed outdoor environments or indoor natural elements or views), and (3)<em> nature exposure plus physical or cognitive task studies </em>(participants performed a task requiring cognitive or physical effort during or after exposure to nature). Two studies that examined <em>brain structure</em> in relation to residential greenness found that higher lifelong exposure to greenness near the home was linked to increased prefrontal cortex (PFC) grey matter volume, which is important for many cognitive and emotional processes. <em>Nature exposure-only studies</em> of brain activity (7 studies) reported decreased brain activity and increased relaxation. For example, brain imaging studies documented decreased PFC activity, indicating reduced stress and increased physiological relaxation, after exposure to nature when compared to other types of environments. Additionally, two studies that measured beta brain waves under these same conditions reported increased beta power, indicating greater alertness. Decreased stress levels were also reported by nature exposure-only studies of the peripheral nervous system. In these studies, exposure to nature conditions was consistently linked to lower sympathetic and higher parasympathetic activity, as well as reduced pulse and heart rate, suggesting that nature exposure has significant stress reducing effects. Overall, findings of nature exposure-only studies suggest a "relaxed yet alert" state compared to urban or indoors conditions. Two studies that examined brain activity during <em>nature exposure plus physical tasks</em> reported that nature exposure was associated with meditative and relaxed states. Similarly, in another study, PFC activity decreased after a walk in a forest as compared to walking in a city, suggesting increased physiological relaxation. Studies that combined <em>nature exposure plus </em><em>cognitive tasks</em> reported increased brain activity, indicating improved attentional processing and cognitive resource allocation. Brain activity assessments suggested that participants demonstrated more effective cognitive resource allocation in nature conditions. For example, the authors of one study concluded “greater cognitive resources were required to complete a spatial working memory task in the indoor classroom setting to achieve the same level of performance as in the outdoor setting.”
The review revealed several important findings about how nature exposure impacts the nervous system for children and youth. The researchers concluded that, overall, “nature exposure was found to be associated with increased grey matter volume in the PFC, brain activity indicating relaxation and alertness in exposure-only conditions as well as improved cognitive resource allocation and attentional processing in exposure plus cognitive task conditions.” These findings offer valuable implications for the field of NBL. Even short exposure to nature during the school day may support optimal learning conditions in which students are relaxed yet alert and better able to maintain attention. Because results were similar across all age groups included in the review, findings encourage the use of NBL for both younger and older students. Additionally, students with behavioral or attentional concerns may especially benefit from nature exposure and NBL approaches that support attention skills and effective cognitive resource allocation.
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