Exploring the Effects of Short-Term Forest Bathing on Anxious Medical Undergraduates' Stressful Emotions Using Near-Infrared Functional Brain Imaging and Facial Expression Technology

Abstract

Abstract: Background: Enrolled medical undergraduates face high exam competition and stress, reducing life quality, well-being, learning abilities and health; supporting their exam stress management is critical. This study used a 2-hour forest bathing intervention to alleviate their exam-related stress. Methods: One week prior to the intervention, 160 students were recruited via university bulletin boards; eligibility screening, defined by a State-Trait Anxiety Inventory-State score >40, was administered one day before the 2-hour sensory exposure. Ultimately, 60 final-examination-preparing medical undergraduates (male:female=7:53) were randomly assigned to two groups (n=30 per group). Analyses focused on oxygenated hemoglobin (oxy-Hb) levels in the prefrontal cortex (PFC), physiological functions, and psychological changes under specific tasks. Results: Forest environments characterized by lower noise levels, and higher negative air ion concentrations—with a comfort index of 0.971–1.368 (vs. 2.221–3.647 in urban areas) and negative oxygen ion concentrations of 1000–1200 ions/cm³ (vs. 400–500 ions/cm³ in urban areas). For the PFC region, forest group had significantly greater oxy-Hb reduction during the Trier Social Stress Test (TSST) (t(29)=3.038, P=0.005). At the channel-specific level, forest group had decreased oxy-Hb in the left PFC and bilateral Frontopolar Area during the TSST, while the urban group exhibited increased oxy-Hb in the right PFC during the MT. No between-group oxy-Hb differences were observed in the Stroop task or rumination task. Forest group showed lower heart rate (F(1, 57)=4.227, P=0.044), salivary cortisol (F(1, 57)=4.590, P=0.036), higher Nature Connection Scale (F(1,57)=4.822, P=0.032), Digit Span Backward Test (F(1, 57)=6.164, P=0.016), Montreal Cognitive Assessment scores (F(1, 57)=12.040, P<0.001), lower Rumination-Reflection Questionnaire (F(1, 57)=11.318, P=0.001)/Perceived Stress Scale scores (F(1,57)=6.076, P=0.017), 56.7% positive facial expressions (U=263.000, n=60, P=0.002), and elevated positive affect (Profile of Mood States: F(1,57)=17.063, P<0.001). Conclusion: Short-term forest bathing reduces physiological stress markers, enhances nature connectedness/positive emotions, alleviates stress via modified cerebral blood flow, and improves memory and reduce cognitive fatigue to a certain extent. As a low-cost, easy-to-implement strategy, it is may recommended for enrolled medical undergraduates' mental health curricula to build sustainable stress management.