Mood and physiological effects of visual stimulation with images of the natural environment in individuals with depressive and anxiety disorders

Nature therapies are gaining attention as non-pharmacological treatments for depression and anxiety disorders, but research on their effectiveness in patients is limited. This study investigates the mood-enhancing effects of visual stimulation with natural environmental images in patients with depression and anxiety disorders. We conducted a randomized crossover comparison trial involving 60 right-handed adult participants with depression or anxiety disorders and receiving outpatient treatment. Visual stimuli of natural environments consisted of green-themed natural images, while the control stimuli featured urban scenes dominated by buildings. The stimulation lasted for 3 min, during which orbital prefrontal brain activity was measured using a 2-channel Near-infrared Spectroscopy (NIRS) system, and heart rate variability was assessed using fingertip accelerated plethysmography. Mood enhancement effects were observed in both the depression and anxiety disorder groups following visual stimulation with natural images. In the depression group, orbital prefrontal oxygenated hemoglobin concentration significantly increased after visual stimulation with natural images, while there were no significant changes in the anxiety group. However, in the anxiety group, a correlation was found between reduced orbital prefrontal oxygenated hemoglobin in response to natural images and increased mood-enhancement. Furthermore, the severity of depressive symptoms did not significantly affect the intervention effects, whereas heightened anxiety symptoms was associated with a smaller mood enhancement effect. Our study demonstrates the benefits of natural image stimulation for patients with depression and anxiety disorders. Differential orbital prefrontal brain activity impacts notwithstanding, both conditions exhibited mood enhancement, affirming the value of natural image stimulation.