Human Health & Plants Research: Which is Better for Your Brain, a Garden, a Green Space, or a Busy Downtown Environment?

A study published in the journal Frontiers in Psychiatry in 20221 compared the effects of passively experiencing three urban settings on mood and the patterns of brain activity of healthy and clinically depressed participants.  The settings were:

  • A therapeutic garden.
  • A green roof space with walking paths with lush greenery accessible to the public.
  • An active downtown area with minimal to no natural features.

The researchers hypothesized that passive exposure to a therapeutic garden would improve the mood of healthy adults and those with mood disorders, including depressive disorders.  The contrast or control treatment was the busy downtown environment lacking natural characteristics.  Exposure to a green space served as an intermediate comparator treatment.

The experimental design was an assessment of participants before and after each treatment using the Profile of Mood States (POMS) self-report questionnaire, electroencephalography (EEG), and functional near-infrared spectroscopy (fNIRS) measurements of brain neuro-electrical activity and hemodynamics.  The location visit (treatment) order was randomized, as were the three specific visualization perspective scenes within each treatment location.  Neuro-electrical activity and hemodynamics data were collected for (2) two one-minute scene viewings for each scene perspective.  Recording of resting state data for one minute preceded each of the two scene perspective viewings.  Participants completed the POMS questionnaire upon first arrival at a treatment location and again after concluding the viewing of the three scene perspectives at each treatment location.  Participants received the three treatments with an average of about nine days between each treatment.

Ninety-two right-handed adults between the ages of 21 and 75 were enrolled in the study, and 52 were female.  Sixty-eight healthy participants were recruited by word of mouth.  For comparison, the Clinical group of 24 participants under treatment for a depressive disorder at the National University Hospital, Department of Psychological Medicine, were referred to the study.  The average age of the Healthy group was 39, and the Clinical group, was 31.  Participant ethnicity was 65% Chinese for the Healthy group and 70% for the Clinical group.

The researchers found that only for the therapeutic garden were the pre- and post-treatment means for total mood disturbance assessments improved, which was true for both the Healthy and Clinical groups.  No statistical differences existed in the pre- and post-treatment mean for the green space and busy downtown treatments for total mood disturbance.  For the POMS negative mood subscale, the therapeutic garden treatment mean score was lowest, while the busy downtown score was the highest.  Over time the negative mood subscale mean score decreased by 22% for both the Healthy and Clinical groups with the therapeutic garden treatment.

Oxy-Hemoglobin signals were lower following the therapeutic garden treatment compared to the busy downtown treatment, but the treatment differences were not statistically significant.  Also, temporal beta asymmetry did not differ between treatments.  A larger sample size may have revealed more treatment differences.  Since treatment exposures were very limited, perhaps exposures could be increased for greater dosage and more significant treatment effects.

Based on the results, the researchers concluded that visiting a therapeutic garden can “constitute an effective and affordable supplement to depression treatment for patients” and “function as a self-care intervention for the healthy population.”

1Olszewska-Guizzo, A., Fogel, A., Escoffier, N., Sia, A., Nakazawa, K., Kumagai, A., Dan, I., Ho, R. (2022). Therapeutic Garden with Contemplative Features Induces Desirable Changes in Mood and Brain Activity in Depressed Adults. Frontiers in Psychiatry, 13:757056.

Charles Guy, Emeritus and Courtesy Professor

Department of Environmental Horticulture, University of Florida