Human Health & Plants Research: Does Gardening Modify Brain Activity and Impact Emotion?

Dr. Charles Guy

There is an enormous body of anecdotal commentary that engaging in activities with plants and gardening provides a number of psychological health and well-being benefits, such as less stress, anxiety, depressive symptomatology, and greater positive affect.  If true, then where, and how do many of the ballyhooed well-being benefits actually occur?

In 2023, the journal HortScience published a study by Lai and colleagues1 that employed functional magnetic resonance imaging (fMRI) of the brain of study participants who engaged in site preparation and sowing, fertilizing, weeding, and watering, and harvesting over six weeks.  Studies involving fMRI of the brain are typically published in neuroscience journals.  Therefore, it is very rare to see a human-subject functional brain imaging study appear in a traditional horticulture journal.  Yet understanding how plants and gardening provide many of the health benefits to people absolutely requires the marriage of advanced neurosciences and horticulture.  Thus, the study by Lai and colleagues1 is groundbreaking (pardon the pun) and is a pioneering first step forward in the field of people-plant interactions.

The researchers set out to evaluate the emotional processing and responses of study participants using fMRI and a self-report psychometric assessment, the Profile of Mood States (POMS).  More specifically, the researchers sought to acquire empirical data on the connection between brain activity (temporal and spatial patterns of activation) and engaging in various horticultural activities.  As good fortune would have it, the gardening site was virtually adjacent to the Imaging Center for Integrated Body, Mind, and Culture Research with a 3T Siemens Magnetom Prisma MRI facility on the campus of the National Taiwan University.

It was just a three-minute walk from the gardening site to the MRI.  Details of the fMRI parameters and data processing can be found in the published article.

The study population of n=23 included 12 male and 11 female participants, with an overall average age of 23.  Participants were between 20 and 30 years old, in good physical and mental health, right-handed, and had normal vision.  Study participants underwent four fMRI scans and completed the POMS questionnaire four times immediately after the following activities: at pre-test, no horticultural activity; after planting site preparation and sowing; following fertilizing, weeding, and watering; and after crop harvesting (post-test).  Comparisons were based on participants having not engaged in any of the horticultural activities.  The experimental phase of the study took place over six weeks at different times between October to January and April to May.

Not surprisingly, resting-state fMRI data revealed that different areas of the right superior temporal gyrus and left inferior frontal gyrus exhibited different regions of interest (ROI) following site preparation and sowing compared with following harvesting in the post-test scan.

Similarly, differences in the spatial distribution of ROI of the left anterior cingulate cortex were observed following site preparation and sowing, fertilizing, weeding, and watering, and following harvesting (post-test).  The researchers concluded that functional connectivity between the left anterior cingulate cortex, right superior temporal gyrus, and the left superior temporal gyrus regions were related to participation in horticultural activities.

Furthermore, the different stages of horticultural activities resulted in different patterns of functional connectivity between the brain regions.  What is important in this study is the effort to show a potential causal relationship between engaging in a horticultural activity and documenting a change in the patterns and locations of resting-state activations in the brain.  Activations (ROI) relate to neuronal activity and the relative levels of oxyhemoglobin and deoxyhemoglobin in localized areas of the brain as clusters of neurons rise and fall in relative activity.

What did the POMS self-report questionnaires reveal about the emotional status of participants?  With each successive stage of the horticultural activities, the scores for the emotional state (higher scores indicate a more negative emotional state) declined to the lowest value after the harvest, suggesting that concomitantly, with changes in the patterns of brain activity, there could be a cause-and-effect linkage.

Therefore, this study is a first step towards understanding how interacting with plants and gardening provides popularly known health and well-being benefits that remain to be systematically quantified and mechanistically understood.

1Lai, P.H., Li, C.W., Hung, S.H., Lee, A.Y., Chang, C.Y. and Tang, H.F., (2023). How do horticultural activities affect brain activation and emotion? Scientific evidence based on functional connectivity. HortScience, 58(1), pp.67-78.

Charles Guy, Emeritus and Courtesy Professor

Department of Environmental Horticulture, University of Florida

Steering Committee, Wilmot Botanical Gardens, University of Florida