Gladwell V., Brown D., Barton J., (2012). The effects of views of nature on autonomic control. European Journal of Applied Physiology, 112(9):3379-3386 Details
There may be more to enjoying the outdoors than people realize. Aside from the benefits of being more physically active, exposure to nature is believed to improve mental health, concentration and attention, and to enhance cognition, self-esteem and mood.
What are the likely physiological mechanisms? The autonomic nervous system (ANS) can have effects on mood and cognition, as well as the better known ANS functions of homeostasis and controlling physiological responses to stress and relaxation.
Gladwell and colleagues (2012) investigated this further in a group of 29 staff and students from the University of Essex. Semi-recumbent subjects were shown a slideshow of nature scenes (5 min) and urban scenes (5 min), and asked to imagine they were in that environment. Blood pressure (Portapres, FMS), ECG and respiration were recorded in LabChart using a PowerLab.
Heart rate variability (HRV) and blood pressure variability frequency domain analyses were performed. Two spectral components were used as indicators of ANS activity; the high frequency range (HF, 0.15-0.4 Hz) and the low frequency spectral power (LF, 0.04–0.15 Hz) were indicators of parasympathetic activity and overall autonomic activity, respectively.
Interestingly, nature scenes compared to scenes of built-up urban areas were statistically more likely to result in relaxation responses in subjects – as revealed by increases in HRV spectral power in the HF range. However, breathing rate and depth, heart rate and blood pressure were unaffected, indicating the subjects were already in a relaxed state. Thus, the findings were specific to subtle increases in parasympathetic tone.
The study was performed without prior exercise or stress-inducing factors, in a controlled laboratory environment free of complicating factors present in a real outdoor environment. Besides showing a strong psychological element in the relaxation response, this study confirms the power of HRV spectral analyses in revealing subtle changes in vagal tone.