Can a nature walk change your brain? Investigating hippocampal brain plasticity after one hour in a forest

Incidence of mental disorders is higher in cities, whereas visits to nature have been reported to be beneficial for mental health and brain function. However, there is a lack of knowledge regarding how exposure to natural and urban environments affects brain structure. To examine the causal relationship between exposure to these environments and hippocampal formation, 60 participants were subjected to a one-hour walk in either natural (forest) or urban environment (busy street), and high-resolution hippocampal imaging was performed before and after the walks. We observed that the participants who walked in the forest showed increases in subiculum volume, a hippocampal subfield involved in stress response inhibition, while no change was observed after the urban walk. However, this result did not withstand Bonferroni correction for multiple comparisons. Furthermore, the increase in subiculum volume after the forest walk was associated with a decrease in self-reported rumination. These results indicate that visits to nature can lead to observable alterations in the brain structure, with potential benefits for mental health and implications for public health and urban planning policies.