The Effect of Cognitive Behavior Therapy-Based Psychotherapy Applied in a Forest Environment on Physiological Changes and Remission of Major Depressive Disorder

OBJECTIVE: Psychotherapeutic intervention combined with pharmacotherapy is helpful for achieving remission of depressive disorder. We developed and tested the effect of cognitive behavior therapy (CBT)-based psychotherapy applied in a forest environment on major depressive disorder. METHODS: We performed 4 sessions during 4 weeks (3 hours/session) in patients with major depressive disorder during pharmacotherapy. For the forest group, sessions were performed in the forest; for the hospital group, sessions were performed in the hospital. The control group was treated with the usual outpatient management. RESULTS: A total of 63 patients completed the study: 23 in the forest group, 19 in the hospital group, and 21 in the control group. Hamilton Rating Scales for Depression (HRSD) scores of the forest group were significantly decreased after 4 sessions compared with controls. Montgomery-Asberg Depression Rating Scales (MADRS) scores of the forest group were significantly decreased compared with both the hospital group and the controls. The remission rate (7 and below in HRSD) of the forest group was 61% (14/23), significantly higher than both the hospital group (21%, 4/19) and the controls (5%, 1/21). In heart rate variability (HRV) analysis, some measurements representing HRV and parasympathetic nerve tone were increased in the forest group after 4 sessions. The salivary cortisol levels of the forest group were significantly decreased. CONCLUSION: CBT-based psychotherapy applied in the forest environment was helpful in the achievement of depression remission, and its effect was superior to that of psychotherapy performed in the hospital and the usual outpatient management. A good environment such as a forest helps improve the effect of psychotherapeutic intervention because it includes various natural instruments and facilitators in the treatment of depression.