People all over the world profess the physical and psychological benefits of gardening and interacting with plants. Given the magnitude of such a vast body of anecdotal support for the therapeutic benefits of engaging in plant-focused activities, there remains limited scientific evidence for the physiological and psychological bases of said therapeutic benefits. It is evident that plants possess beauty, chemical, and physical features that can provide sensory stimulation that may elicit and contribute to therapeutic and quality-of-life benefits. Understanding how interactions with plants result in mental and physical health therapeutic benefits is key to optimizing treatment protocols for maximum efficacy and meaningful health outcomes.
Kim and Park1 recently reported on a study in the journal PLOS One that aimed to measure how the physical characteristics of 12 different plants representing four types of foliage classified as soft, smooth, stiff, or rough influence the oxy-hemoglobin (oxy-Hb) levels in the prefrontal cortex (PFC) region of the brain, and the participant’s psychological responses relating to relaxation and comfort following a 90-second tactile stimulation of touching an individual plant’s foliage. The PFC is the part of the brain that controls many cognitive functions, attention, learning, and emotions and is associated with a number of psychiatric disorders.
Plants with strong fragrances were excluded from the study. The plants included in the study were not in flower and had an aerial portion only of light energy-collecting foliage. Oxy-hemoglobin levels in participants’ prefrontal cortex were assessed using functional near-infrared spectroscopy (fNIRS). Psychological responses were evaluated using the Semantic Differential Method (SDM) self-report questionnaire.
A total of 30 participants were recruited into the study. Half were male, and half were female. All were right-handed, did not have plant allergies, and were in their 20s. Participants did not consume caffeine for three hours before initiating the experimental treatment.
The experimental treatments were administered in a 2.0 m x 2.0 m compartment with an ambient temperature of 23-26°C, 30% relative humidity, a constant light level of 700 Lux, and a low noise level. Participants wore the fNIRS apparatus throughout the encounter with plants. Following a 3-minute rest period to collect a fNIRS baseline measurement, participants next engaged in tactile stimulation contact with a plant’s foliage for 90 seconds. Then, participants completed the self-report questionnaire. The sequence was repeated until all 12 plants had been experienced.
What were the experimental results? Would touching foliage with different physical properties influence measured oxy-Hb levels in the prefrontal cortex? Yes, it did. The highest oxy-Hb occurred in the prefrontal cortex when touching soft foliage, and the lowest when touching smooth foliage. There were some differences in the responses in the left and right PFC regions. With a larger overall sample size, it may have been possible to realize more differences when comparing the responses of the right and left PFC regions. In men, oxy-Hb in the PFC was significantly higher for soft foliage compared to smooth, stiff, and rough foliages, but not different in women. However, the oxy-Hb level in the PFC for men for soft foliage was much greater than for women, indicating a sex-based differential neurological response to tactile stimulation from soft foliage.
The results from the SDM questionnaire revealed that tactile stimulation by soft and smooth foliage was most relaxing and provided the most comfort for participants. There were also some sex-based differences for soft foliage.
The authors suggest that the present findings align with other studies that show that smooth textures promote calming effects, perhaps by reducing neural activation in the PFC. The findings from the SDM questionnaire on calming and relaxation appear to reinforce some of the oxy-Hb physiological responses.
This study is critically important because its findings open a window on what happens neurologically in response to touching plants with differing textures and provide a springboard for further studies that seek to understand the mechanisms that account for the therapeutic benefits of plant-based activities that gardeners and plant enthusiasts so often profess.
1Kim S-H, Park S-A (2025). Psychophysiological and Psychological Responses of Touching Plant Behavior by Tactile Stimulation According to the Foliage Type. PLoS ONE 20(2): e0316660. https://doi.org/10.1371/journal.pone.0316660
Charles Guy, Emeritus and Courtesy Professor
Department of Environmental Horticulture, University of Florida
Steering Committee, Wilmot Botanical Gardens, University of Florida