The desire to understand does not end with mere curiosity; it extends into neuroscience, psychology, and urban planning as we seek to comprehend how our environment shapes the human brain. In recent years, a growing body of research has illuminated the  effects of nature on mental health, cognitive function, and even brain structure. Three studies have advanced this understanding, revealing that exposure to natural environments and time spent outdoors can lead to measurable changes in the brain, potentially mitigating the adverse effects of urban living.

Urbanization has brought significant lifestyle changes, with more than half of the global population residing in cities. While urban living offers numerous advantages, studies indicate that it also correlates with increased stress, anxiety, and mood disorders. The investigation into how exposure to natural versus urban environments affects brain function and structure has become an essential area of research.

One of the studies in this field, Can a Nature Walk Change Your Brain? Investigating Hippocampal Brain Plasticity After One Hour in a Forest (Sudimac & Kühn, 2024), explores the impact of a brief forest walk on the hippocampus, a brain region crucial for memory and emotional regulation. Their findings demonstrate that participants who spent one hour walking in a forest showed an increase in the subiculum volume, a subfield of the hippocampus associated with stress regulation. Conversely, those who walked in an urban setting displayed no such change. Moreover, the study identified a correlation between increased subiculum volume and reduced rumination, a common precursor to depression. While these findings underscore nature’s role in promoting brain plasticity, the authors acknowledge that further research is needed to establish the long-term implications of these structural changes.

A second study, Structural and Functional Neural Basis of Urbanicity and Green Space in the Neighborhood of Older Adults (Kühn et al., 2021), delves into the structural impact of urban environments on the aging brain. Examining a sample of 207 older adults, the study found that higher levels of urban fabric (built environments) correlated with reduced grey matter volume in the perigenual/subgenual anterior cingulate cortex (p/sACC), a region implicated in emotional regulation and mental health. Conversely, greater access to green spaces was associated with increased grey matter volume in the same region. These results suggest that the presence of green areas can counteract some of the negative effects of urban living, offering potential neuroprotective benefits. However, intriguingly, the study did not find direct correlations between brain structure changes and self-reported mental health metrics, indicating that the relationship between environment, brain health, and subjective well-being is multifaceted and warrants further exploration.

Expanding on the concept of environmental influence on the brain, Spend Time Outdoors for Your Brain: An In-Depth Longitudinal MRI Study (Kühn et al., 2022) presents compelling evidence of the neuroplastic benefits of outdoor exposure. This longitudinal study involved six participants who underwent 40-50 MRI scans over six to eight months, allowing for an unprecedented analysis of day-to-day variations in brain structure. The researchers found that time spent outdoors was positively associated with increased grey matter volume in the right dorsolateral prefrontal cortex (DLPFC), a region involved in executive function and emotional regulation. Notably, these structural changes persisted even after controlling for confounding variables such as physical activity, sunshine exposure, and free time. Additionally, spending more time outdoors was linked to enhanced positive affect, further supporting the argument that nature plays a critical role in mental well-being.

The convergence of these three studies underscores the  impact of natural environments on brain structure and function. The findings suggest that even short-term exposure to nature can induce measurable changes in brain plasticity, particularly in regions associated with stress regulation, executive function, and emotional well-being. These insights hold significant implications for mental health interventions, advocating for the integration of nature-based therapies, such as guided forest walks, into treatment plans for stress-related disorders.

Moreover, the research highlights the necessity of incorporating green spaces into urban design. City planners and policymakers should prioritize accessible, high-quality natural areas to promote cognitive health and emotional well-being among urban residents. This approach aligns with the growing advocacy for “green prescriptions,” wherein healthcare providers encourage individuals to spend time in nature as a preventive and therapeutic measure.

In addition, these findings underscore the critical role of Shinrin Yoku Guides, Forest Therapy Practitioners, and Forest Bathing Guides in advancing scientific and therapeutic applications of nature immersion. By employing structured, evidence-based techniques, these practitioners facilitate nature interactions that optimize cognitive and emotional benefits. Shinrin Yoku, or “forest bathing,” engages participants in multisensory environmental exposure, which has been shown to influence the autonomic nervous system, reducing cortisol levels, improving heart rate variability, and enhancing parasympathetic nervous activity.

Furthermore, guided forest therapy sessions can be tailored for clinical applications, supporting individuals with anxiety, depression, and stress-related disorders. By integrating neurobiological insights into their practice, Shinrin Yoku Guides can refine methodologies to enhance neuroplasticity, attentional restoration, and affective regulation. This interdisciplinary approach strengthens the bridge between ecopsychology, neurophysiology, and environmental health, positioning forest therapy as a scientifically grounded, effective intervention for mental well-being.

Attention Restoration Theory and Its Overlap with Neuroplasticity Research

Attention Restoration Theory (ART), proposed by Kaplan and Kaplan (1989), posits that exposure to natural environments facilitates cognitive recovery by reducing mental fatigue and restoring directed attention. According to ART, the effortless fascination elicited by nature promotes involuntary attention, allowing the brain’s executive functions to replenish. This seems to align with findings from the three studies discussed, particularly regarding the role of nature exposure in enhancing cognitive function and emotional regulation.

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The study by Sudimac & Kühn (2024) demonstrated that walking in a forest increased hippocampal subiculum volume, a region associated with stress regulation. ART suggests that natural environments demand less directed attention, reducing cognitive load and indirectly promoting structural changes in brain regions linked to emotional well-being. Similarly, Kühn et al. (2021) found that greater access to urban green spaces correlated with increased grey matter volume in the perigenual/subgenual anterior cingulate cortex (p/sACC), a region associated with emotional regulation. ART seems to support this by emphasizing that exposure to restorative environments minimizes stressors that require constant executive control, thereby allowing emotional processing centers to function more efficiently.

The longitudinal study by Kühn et al. (2022) demonstrated increased dorsolateral prefrontal cortex (DLPFC) volume with time spent outdoors. While ART primarily focuses on attentional recovery rather than structural brain plasticity, its principles provide a framework for understanding why regular outdoor exposure fosters neuroplastic changes. The overlap suggests that attentional restoration may be a cognitive mechanism underlying the observed structural benefits in these studies, reinforcing the role of nature in both immediate cognitive function and long-term brain health.

Mechanisms Behind Stress Reduction and Nervous System Regulation Through Forest Exposure

Exposure to forest environments has been shown to activate also the parasympathetic nervous system (PNS) while down-regulating the sympathetic nervous system (SNS), leading to measurable physiological and neurobiological benefits. This process, the biophilic stress-reduction effect, is facilitated through multiple mechanisms, including reduced cortisol levels, decreased heart rate, and enhanced heart rate variability, all of which contribute to a state of relaxation and psychological well-being.

One key factor in stress reduction through nature exposure is the impact of phytoncides, volatile organic compounds emitted by trees and plants. Studies have found that inhalation of these compounds can enhance natural killer (NK) cell activity, bolstering immune function while simultaneously lowering stress biomarkers such as salivary cortisol and adrenaline. This aligns with findings from Sudimac & Kühn (2024), in which forest walks were associated with hippocampal plasticity and decreased rumination—factors linked to the modulation of the hypothalamic-pituitary-adrenal (HPA) axis.

Additionally, nature’s sensory engagement plays a role in nervous system regulation. Soft fascination, as outlined in Attention Restoration Theory (ART), allows for a shift from hyperactive prefrontal cortical activity to a more relaxed neural state. The work of Kühn et al. (2021) on urban green spaces and brain structure further supports this by demonstrating that increased access to green environments correlates with greater grey matter volume in regions associated with emotional regulation, suggesting a tangible neurobiological impact of nature exposure.

The auditory landscape of forests also influences nervous system activity. Natural sounds, such as flowing water and bird calls, have been found to decrease the amygdala’s response to stress while promoting relaxation through increased vagal nerve activity. This could partially explain why time spent in green spaces, as demonstrated in the longitudinal study by Kühn et al. (2022), was associated with structural enhancements in the dorsolateral prefrontal cortex (DLPFC), a region involved in stress modulation and cognitive control.

Taken together, these mechanisms highlight how forest exposure directly influences markers of stress and nervous system function, reinforcing the need for integrative approaches that bridge neuroscience, environmental psychology, and forest therapy interventions.

The Role of the Prefrontal Cortex and Limbic System

The prefrontal cortex (PFC) plays a crucial role in cognitive control, emotional regulation, and executive function. Chronic urban stress has been linked to hyperactivity in the PFC, contributing to cognitive fatigue and decreased attentional capacity. Studies, such as those by Kühn et al. (2022), suggest that time spent in natural environments reduces excessive PFC activation, allowing the brain to recover from mental overload. Additionally, the dorsolateral prefrontal cortex (DLPFC), which is involved in working memory and decision-making, exhibits structural changes following prolonged exposure to green environments, further supporting cognitive restoration and improved executive function.

The limbic system, particularly the amygdala and hippocampus, also plays a significant role in stress regulation and memory processing. The study by Sudimac & Kühn (2024) found that participants who walked in a forest exhibited increased hippocampal subiculum volume, which is associated with reduced stress and improved emotional resilience. The amygdala, a key structure in processing fear and stress, shows reduced activation during nature exposure, as supported by previous neuroimaging studies, indicating a direct neural response to natural stimuli that fosters relaxation.

Neurotransmitters and Hormonal Pathways

Forest environments also influence key neurotransmitters and hormonal systems that mediate stress and relaxation. Increased dopamine and serotonin levels have been observed following nature exposure, enhancing mood and motivation while mitigating symptoms of anxiety and depression. Additionally, the hypothalamic-pituitary-adrenal (HPA) axis, which governs the body’s stress response by releasing cortisol, exhibits reduced activation when individuals spend time in nature, leading to lower cortisol levels and decreased physiological stress.

Vagal Activation and the Role of the Vagus Nerve

The vagus nerve, a crucial component of the parasympathetic nervous system, is significantly influenced by nature exposure. Vagal tone, which is a measure of parasympathetic nervous activity, has been shown to increase in forest environments. This is evidenced by improved heart rate variability (HRV), which reflects a more adaptive and resilient nervous system. Increased HRV is associated with better stress recovery, reduced inflammation, and enhanced emotional regulation.

Moreover, the auditory and olfactory stimuli found in forests contribute to this effect. The gentle sounds of rustling leaves and flowing water activate alpha brain waves, which are associated with a meditative and relaxed state. Simultaneously, inhalation of phytoncides—volatile organic compounds released by trees—has been shown to further enhance parasympathetic activation and immune function.

The cumulative effect of these neural and autonomic processes underscores the scientific foundation of Shinrin Yoku (forest bathing, forest therapy). By engaging the brain’s regulatory networks and shifting autonomic balance, spending time in natural environments offers a multifaceted therapeutic approach to stress management and mental clarity,.

Future Research Directions

While these studies provide compelling evidence of the brain’s responsiveness to environmental stimuli, several questions remain. Future research should explore the long-term effects of nature exposure on brain structure, particularly in clinical populations with anxiety and mood disorders. Additionally, further investigation is needed to determine the optimal duration and type of nature exposure required to maximize its benefits. Longitudinal studies with larger sample sizes and diverse populations will be crucial in validating these findings and translating them into actionable public health strategies.

The desire to understand the intricate relationship between the human brain and its environment continues to drive scientific inquiry. The evidence presented by these three studies reaffirms the vital role that nature plays in shaping brain structure, reducing stress, and enhancing mental well-being. As urbanization continues to expand, integrating natural elements into daily life may be one of the most effective strategies for fostering a healthier, more resilient society. By embracing nature’s potential, we can move toward a future where urban landscapes harmonize with human well-being.