Introduction
Dementia is a chronic and progressive neurological disorder with multifactorial etiologies, characterized by a decline in memory, cognitive function, behavior, and daily living skills (Kester and Scheltens, 2009). In Korea, the rapid increase in the aging population, particularly those 65 and older, has led to a corresponding rise in the number of dementia cases, propelling the nation into the state of a super-aged society. This demographic shift highlights the urgent need for effective dementia prevention strategies (Kim et al., 2023). Consequently, various cognitive enhancement activities have been proposed as preventive measures against dementia (Van de Winckel et al., 2004; Gross et al., 2012; Han et al., 2016; Murroni et al., 2021). Since the 2000s, there has been a growing focus on approaches that utilize the therapeutic benefits of natural environments for health promotion. The therapeutic benefits of nature-based activities for older adults with dementia and cognitive impairments have been well-documented in numerous studies (Lim et al., 2021; Murroni et al., 2021; Baek et al., 2022). These studies indicate that nature-based activities are effective in reducing stress, enhancing mood, and improving cognitive function in individuals with dementia and cognitive disorders. Based on these findings, many of the developed countries such as the United Kingdom, the United States, and Australia are increasingly integrating natural therapeutic approaches, including gardening activities, into their national healthcare policies (Aggar et al., 2021; Lejac, 2021; Public Health England, 2021; N.H.S. England, 2022).
Nature-based activities for dementia patients are typically categorized into indoor and outdoor activities. As evidence grew in the late 1990s that growing plants in indoor environments had positive effects on psychological stability and the reduction of physiological stress, research into the cognitive and emotional benefits of indoor horticultural activities became increasingly prevalent. With rising interest in outdoor nature experiences in the 2000s, studies investigating the psychological and physiological benefits of outdoor gardening activities gained momentum (Clatworthy et al., 2013; Soga et al., 2017). Indoor horticultural activities typically involve activities such as planting and crafting, primarily focused on ornamental plants, and are conducted within indoor settings (Lee and Kim, 2008; Detweiler et al., 2012). In contrast, outdoor gardening takes place in open-air settings, and includes interactions with a variety of plants and the broader natural environment (Triguero-Mas et al., 2015; Franco et al., 2017). These environmental differences can significantly influence psychological and physiological responses to specific activities (Bowler et al., 2010; McSweeney et al., 2021). Recent studies have highlighted that outdoor gardening activities substantially enhance cognitive function, improve emotional well-being, and promote social interaction (Gonzalez and Kirkevold, 2014; Pasanen et al., 2018). Consequently, there is a growing body of research indicating that outdoor gardening activities not only improve cognitive function and quality of life in dementia patients but also provide significant stress reduction benefits. Most studies evaluating the effects of outdoor gardening activities on elderly individuals with dementia and mild cognitive impairment have used cognitive function assessments, such as the Mini-Mental State Examination (MMSE), alongside psychological questionnaires and blood pressure measurements (Lee and Kim, 2008; Erickson et al., 2011; Luk et al., 2011; Han et al., 2018; Borella et al., 2023). However, the impaired cognitive function of elderly individuals with dementia often poses a challenge when conducting complex psychological assessments. This limitation may explain the lack of diversity in the metrics used in current research on nature-based activities for dementia. Consequently, some studies have shifted their focus directly to the brain, particularly by examining cerebral blood flow changes in dementia patients, to evaluate the effects of gardening activities. These studies have utilized markers such as Brain-Derived Neurotrophic Factor (Ng et al., 2018; Park et al., 2019), electroencephalography (Kim et al., 2021; Du et al., 2022), and Functional Magnetic Resonance Imaging (Lentoor, 2024) to clarify the benefits of gardening activities. Yet despite dementia’s strong association with brain function, studies indicate that field research data on brain activation related to gardening activities as a therapeutic intervention for dementia patients remains insufficient (Park et al., 2019; Lentoor, 2024).
Neuroscientific studies indicate that the prefrontal cortex (PFC) is actively involved in performing cognitive tasks, with its activation closely linked to working memory, decision-making, and emotional regulation (Bechara et al., 2000; Miller and Cohen, 2001; Barbey et al., 2011). Specifically, the dorsolateral prefrontal cortex (DLPFC) is associated with working memory and cognitive control, the ventrolateral prefrontal cortex (VLPFC) with emotional responses and stress regulation, and the lateral orbitofrontal cortex (LOFC) with decision-making and social behavior (Bechara et al., 2000; Miller and Cohen, 2001; Goldman-Rakic, 2011; Yeo et al., 2018). In dementia patients, reduced activation in these regions indicates cognitive decline (Pievani et al., 2014), while activation in these areas suggests an improvement in cognitive function (Beishon et al., 2017). From this perspective, gardening activities are considered effective in enhancing cognitive function by stimulating various brain regions through diverse sensory inputs. The colors, fragrances, and textures of plants stimulate vision, smell, and touch, respectively, which can promote the activation of the frontal lobe (Lee, 2017; Jo et al., 2019). Additionally, gardening involves physical activity, which can contribute to increased cerebral blood flow and improved brain function (Park et al., 2014; Lentoor, 2024). Yet despite the prefrontal cortex (PFC) frequently being mentioned in dementia-related medical trials for its role in cognitive function and emotional regulation (Maillet and Rajah, 2013; Metzger et al., 2016), studies on blood hemodynamics in this region remain extremely rare. Previous studies examining cerebral blood flow changes during outdoor gardening activities have primarily focused on general adults or elderly populations (Toyoda et al., 2017; Park et al., 2019; Lee et al., 2021; Lai et al., 2023). However, as these studies were mainly conducted on younger adults or healthy elderly individuals, the hemodynamic responses observed may differ from those in elderly individuals with dementia and cognitive impairments (Lu et al., 2011; Maillet and Rajah, 2013; Metzger et al., 2016). For this reason, more specific research is required to better understand cerebral blood flow responses in dementia patients. Notably, since different regions of the prefrontal cortex are responsible for distinct functions, it is essential to explore the activation or de-activation of specific regions of PFC and the connectivity of them in greater depth.
Therefore, this study was conducted to assess the degree of brain activation during outdoor gardening activities in elderly individuals with dementia and mild cognitive impairment. To achieve this, oxyhemoglobin responses were measured using near-infrared spectroscopy (NIRS), and the activation levels of the frontal lobe were subsequently evaluated. Additionally, to analyze the effects of cognitive function improvement, blood flow changes in specific prefrontal cortex (PFC) regions were examined based on the type of activity, and connectivity analysis of each prefrontal cortex region was also conducted. The primary goal of this study was to quantify the cerebral activation patterns associated with outdoor gardening activities in comparison to general indoor dementia prevention activities, thereby evaluating the effectiveness of gardening in preventing dementia and enhancing cognitive function.
Research Methods
Participants
This study aimed to evaluate the effects of gardening activities on cognitive function improvement in elderly individuals with dementia and mild cognitive impairment. A total of 23 participants (male and female) were enrolled in the study, with 11 participants assigned to the gardening activity group (average age 80.6 ± 5.4 years) and 12 participants to the indoor cognitive training group (average age 84.5 ± 2.5 years). All participants were selected from among individuals diagnosed with early-stage dementia and mild cognitive impairment registered with the National Dementia Safety Center. The sample size was determined based on previous research, with consideration given to statistical significance and the feasibility of field experiments. The selection of 23 participants was guided by prior studies that utilized sample sizes ranging from 6 to 15 participants (Ng et al., 2018; Park et al., 2019; Kim et al., 2021), indicating that this number would be sufficient to achieve statistical significance. To further enhance the statistical power and ensure the robustness of the findings, a sample size of 23 was chosen. Previous research investigating the effects of gardening on brain activation in healthy adults has employed sample sizes between 15 and 23 participants (Kotozaki, 2020; Lai, 2023), which further supports the appropriateness of the selected sample size for this study. The study was conducted following approval from the Joint Bioethics Committee, and adhered to the guidelines of the Declaration of Helsinki (P01-202309-01-041).
Research sites
This study was conducted in the fall of 2023 at two different sites: an outdoor garden and an indoor seniors’ center. The gardening activity group carried out their activities in a 2,800 Home m2 Garden within the Sejong National Arboretum, while the control group participated in activities at a 30m2 seniors’ center in Sejong City. To facilitate cognitive training activities, tables and chairs were arranged in the seniors’ center. Environmental conditions were carefully regulated to maintain consistency between the two locations, and on the day of the experiment, temperature and humidity were recorded at 24.6 ± 2.0°C and 54.5 ± 4.5% in the Home Garden and 24.0 ± 1.4°C and 52.9 ± 3.6% in the seniors’ center. All experimental settings were thoroughly inspected in advance to eliminate potential safety hazards and ensure a controlled, secure environment. Additionally, a designated waiting area was provided to minimize participant fatigue and ensure a comfortable resting environment throughout the study.
Procedure and Stimuli
Prior to the study, all participants were provided with a detailed explanation of the research, and informed consent was obtained through written consent forms. To ensure optimal conditions and the efficient progress of the study, all experiments were conducted under the supervision of healthcare experts. Each participant was equipped with near-infrared spectroscopy devices (NIRIT LITE, OBELAB, Korea) and seated for a two-minute stabilization period. This was followed by a 10-minute activity session, during which cerebral blood flow responses were continuously monitored using near-infrared spectroscopy (Fig. 1). Each group’s activities were designed to stimulate fine motor skills while seated, aimed at improving cognitive function in elderly individuals with dementia and cognitive impairment (Table 1). The outdoor gardening activity group (hereinafter referred to as OGA) participated in planting flowers and seedlings in bed planters, while the indoor cognitive training group (hereinafter referred to as ICT) engaged in an artistic painting activity for seniors with cognitive disorders. The “artistic painting activity for seniors” involves coloring specific areas of a design according to assigned numbers using colored pencils, a method commonly used to enhance cognitive function in elderly individuals with dementia and cognitive impairments (Glozman and Naumova, 2014; Hunt et al., 2018).
Measurement
Near-infrared spectroscopy (hereinafter referred to as NIRS) is a non-invasive technique that utilizes near-infrared light (700 to 1,000 nm) to measure changes in hemoglobin concentration in the prefrontal cortex (hereinafter referred to as PFC), thereby assessing cortical activation (Toyoda et al., 2017; Kang et al., 2022). NIRS allows for the rapid evaluation of frontal lobe function by measuring blood flow in the PFC, with the added advantage of being applicable in both indoor and outdoor settings. In the present study, NIRS was employed to observe changes in oxyhemoglobin concentration, building on previous findings from neurosurgery clinical studies (Risacher et al., 2011; Metzger et al., 2016) that demonstrated slower cortical activation in frontal lobe areas, such as the lateral frontal cortex, in dementia patients compared to healthy adults. The NIRSIT LITE device (OBELAB Inc., Seoul, Korea) with 15 channels was used, and measurements were taken after securely attaching the device to the center of the forehead, approximately 1 cm above the subject’s eyebrows, to minimize light interference. The reliability of the NIRSIT LITE device has been validated in several studies assessing its performance in detecting changes in brain activity, particularly within the field of medical science (Khoe et al., 2020; Youn et al., 2022; Kang et al., 2022; Kim et al., 2023; Park et al., 2023). These studies have confirmed the device’s accuracy and effectiveness in clinical and experimental settings, establishing its utility in assessing cortical activation and hemodynamic responses. Furthermore, accuracy studies conducted by Trakoolwilaiwan et al. (2016) and Yao et al. (2022) reported that the NIRSIT device achieved accuracy rates of 80% and 76.67%, respectively, further supporting its reliability in neuroimaging applications.
In addition, the Subjective Memory Complaints Questionnaire (hereinafter referred to as SMCQ) and the Korean version of the Short Form of the Geriatric Depression Scale (hereinafter referred to as SGDS-K) were used to assess the homogeneity between the two groups (ICT and OGA) prior to the experiment. The SMCQ consists of 14 items designed to assess subjective memory decline (Youn et al., 2009), while the SGDS-K is a 15-item questionnaire used to measure depression levels in elderly individuals (Cho et al., 1999). Both questionnaires utilize a binary response format (“Yes” or “No”), making them suitable for participants with dementia and mild cognitive impairment. In the present study, the internal consistency of the questionnaires was evaluated using Cronbach’s α, yielding reliability coefficients of 0.812 for the SMCQ and 0.717 for the SGDS-K, thus demonstrating acceptable levels of reliability.
Data analysis
In this study, the blood flow response was analyzed by focusing on changes in specific regions of the PFC to quantify the impact of cognitive enhancement activities on brain function in elderly individuals with dementia and cognitive impairment. To analyze the NIRS data, the raw data collected underwent various stages of preprocessing. First, to handle invalid values in the raw intensity data, nearest-neighbor interpolation was applied where there were no more than five consecutive invalid values. Channels with more than five invalid values were excluded from the analysis. The raw intensity data were then converted into optical density (Yücel et al., 2021). To remove motion artifacts from the converted optical density data, the Temporal Derivative Distribution Repair (TDDR) method was applied (Fishburn et al., 2019). Additionally, single-channel regression was utilized to reduce superficial noise. The average of channels with a source-detector distance of 8 mm or less was used as a regressor to eliminate short-separation signals, thereby improving the statistical significance of the hemodynamic response (Gagnon et al., 2013). The optical density data were subsequently converted into hemoglobin concentration using Differential Pathlength Factors (DPFs) estimated based on the age of each participant, with molar extinction coefficients calculated by Moaveni (Zhao et al., 2017). Hemoglobin concentration was expressed in μM (micromolar) units (Delpy et al., 1988; Cope and Delpy, 1988). The converted hemoglobin concentration data were then digitally filtered to remove physiological noise and measurement noise/drift, with a bandpass filter set to a low cutoff frequency of 0.005 Hz and a high cutoff frequency of 0.1 Hz (Yücel et al., 2021). Finally, rejection padding was employed, replacing missing data with the average of nearby channels or the overall average of the remaining channels. The preprocessing was conducted using the NIRSIT Quest program (OBELAB Inc., Seoul, Korea), and the preprocessed data were statistically analyzed using SPSS version 21.0 (IBM, USA). To analyze blood flow changes in specific regions of the PFC, we categorized 15 channels based on findings from cognitive neuroscience research (Bechara et al., 2000; Risacher et al., 2011; Metzger et al., 2016; Toyoda et al., 2017; Yeo et al., 2018) and the Clustering 2 criteria in the NIRSIT Quest program (Fig. 2). Specifically, the channels were categorized as follows: four lateral channels corresponding to the ventrolateral PFC (hereinafter referred to as VLPFC), six upper channels corresponding to the dorsolateral PFC (hereinafter referred to as DLPFC), four lower channels corresponding to the lateral orbitofrontal cortex (hereinafter referred to as LOFC), and one channel corresponding to the frontopolar PFC (hereinafter referred to as FP-PFC). All active data were baseline-corrected by setting the baseline to the 2-minute value corresponding to the pre-activity stabilization phase, and changes in blood flow during the activity were calculated relative to this baseline. Prior to the experiment, a preliminary assessment was conducted using the SMCQ and the SGDS-K to ensure homogeneity between the two groups, with the homogeneity of variances confirmed using the Chi-square test. The results of the pre-assessment showed that the variances between the two groups (ICT and OGA) were homogeneous for both the SCMQ (Pearson χ2 = 13.783, df = 8, p = .088) and the SGDS-K (Pearson χ2 = 9.641, df = 12, p = .647). Based on these preliminary test results, the research was conducted with homogeneity between the two groups confirmed. The comparison of oxyhemoglobin (Oxy-Hb) concentration levels for PFC blood flow analysis was guided by previous studies that employed NIRS to assess changes in cerebral blood flow (Lee, 2017; Youn et al., 2024). The average concentration levels during ICT and OGA activities, as well as the comparison of blood flow changes across the early, middle, and late phases of the activities (based on 200-second averages), were analyzed using paired t-tests. All results are presented as mean ± standard error (SE), with the statistical significance level set at p < .05.
Results
Mean blood flow changes in the prefrontal cortex by activity type
During each cognitive enhancement activity (ICT vs. OGA), significant differences in blood flow changes were observed across various regions of the PFC (Table 2). When comparing the average changes in Oxy-Hb concentration across Total PFC regions during the 10-minute activity, OGA demonstrated a significantly higher concentration compared to ICT (ICT, −0.029 ± 0.001 μM; OGA, 0.017 ± 0.002 μM, p < .001). An increase in Oxy-Hb concentration indicates an increase in blood flow, suggesting that OGA elicited a stronger blood flow response than ICT. Further analysis of the average Oxy-Hb concentration changes at specific sites revealed significantly higher blood flow responses in the right VLPFC (Lateral) (ICT, −0.046 ± 0.002 μM; OGA, 0.105 ± 0.005 μM, p < .001), the right and left DLPFC (Upper) (Right: ICT, 0.079 ± 0.002 μM; OGA, 0.096 ± 0.004 μM, p < .001; Left: ICT, −0.168 ± 0.001 μM; OGA, 0.000 ± 0.004 μM, p < .001), and the right LOFC (Lower) (ICT, −0.070 ± 0.001 μM; OGA, 0.043 ± 0.004 μM, p < .001), as well as the FP-PFC (Center) (ICT, 0.095 ± 0.002 μM; OGA, 0.462 ± 0.005 μM, p < .001). Conversely, in the left VLPFC (Lateral) (ICT, 0.040 ± 0.002 μM; OGA, −0.213 ± 0.004 μM, p < .001) and the left LOFC (Lower) (ICT, −0.054 ± 0.001 μM; OGA, −0.173 ± 0.004 μM, p < .001), a lower blood flow response was observed during OGA compared to ICT.
Time-series changes in prefrontal cortex regions by activity type
Fig. 3 illustrates the time-series changes in Oxy-Hb concentration across various regions of the PFC during the 10-minute activity in 23 elderly participants with dementia and cognitive impairment. To enable a more detailed analysis, the 10-minute duration was divided into early, middle, and late phases, each represented by 200-second averages, which are presented in Table 3 to compare the concentration changes in each PFC region during ICT and OGA activities. The analysis of time-series changes in Oxy-Hb concentration across PFC regions during the two activities (ICT vs. OGA) over the 10-minute period revealed consistently higher Oxy-Hb concentrations in OGA. In Total PFC, the ICT group showed a slight increase in Oxy-Hb concentration, from −0.032 ± 0.001 μM (000–200s) to −0.025 ± 0.002 μM (400–600s). In contrast, the OGA group demonstrated a significant increase over the same period, from 0.013 ± 0.004 μM (000–200s) to 0.021 ± 0.004 μM (400–600s) (000–200s, t = −11.25, p < .001; 400–600s, t = −10.86, p < .001).
In specific PFC regions, the right VLPFC in the ICT group showed a slight increase in Oxy-Hb concentration, from −0.051 ± 0.003 μM (000–200s) to −0.036 ± 0.003 μM (400–600s), although overall blood flow remained low. Conversely, the OGA group exhibited a slight decrease, from 0.120 ± 0.009 μM (000–200s) to 0.084 ± 0.008 μM (400–600s), but maintained a consistently higher average blood flow throughout the entire period (p < .001). In the 10-minute average analysis, the left VLPFC, which showed lower blood flow responses in the OGA group compared to the ICT group, also demonstrated generally lower Oxy-Hb concentrations in the 200-second average comparison. However, as the activity progressed, the ICT group exhibited a decrease in Oxy-Hb concentration, from 0.040 ± 0.002 μM (000–200s) to 0.027 ± 0.003 μM (400–600s), while the OGA group showed an increasing trend, from −0.264 ± 0.008 μM (000–200s) to −0.180 ± 0.004 μM (400–600s) (p < .001). In contrast, in the right DLPFC, the OGA group initially showed a higher Oxy-Hb concentration (0.113 ± 0.006 μM) compared to the ICT group (0.069 ± 0.003 μM) during the early phase (000–200s). However, as the activity progressed into the later phase (400–600s), the ICT group exhibited a greater increase in blood flow (0.086 ± 0.004 μM) compared to the OGA group (0.068 ± 0.009 μM) (p < .001). In the left DLPFC, both the ICT group (000–200s, −0.172 ± 0.002 μM; 400–600s, −0.161 ± 0.003 μM) and the OGA group (000–200s, −0.027 ± 0.006 μM; 400–600s, 0.030 ± 0.008 μM) showed an increase in blood flow over time, with a more pronounced increase observed in the OGA group (p < .001). Comparing the early and late phases of activity in the right LOFC, the ICT group showed a slight decrease, from −0.070 ± 0.001 μM to −0.067 ± 0.002 μM, whereas the OGA group demonstrated a significant increase, from 0.048 ± 0.037 μM to 0.179 ± 0.033 μM (p < 0.001). In the left LOFC, the ICT group also exhibited a decrease, from −0.054 ± 0.001 μM to −0.051 ± 0.002 μM, while the OGA group showed an increase, from −0.201 ± 0.008 μM to −0.151 ± 0.005 μM p < .001). In the PF-PFC, the Oxy-Hb concentration in the ICT group remained relatively stable, increasing slightly from 0.095 ± 0.002 μM to 0.099 ± 0.003 μM, whereas the OGA group showed a substantial increase, from 0.462 ± 0.046 μM to 0.463 ± 0.283 μM (p < .001).
In the time-series analysis, the OGA group exhibited higher Oxy-Hb concentrations in the right VLPFC and right LOFC during the initial 200-second phase compared to the ICT group, with a consistent increasing trend observed in the middle (200–400s) and late (400–600s) phases as well. In the left DLPFC, there was a marked increase in Oxy-Hb concentration in the OGA group during the late phase (400–600s). For the right DLPFC and PF-PFC, both groups maintained stable Oxy-Hb concentrations, although a slight increase was observed in the OGA group. Notably, in the left VLPFC and left LOFC, while the OGA group initially showed lower blood flow changes during the early phase (000–200s), a trend of increasing Oxy-Hb concentration was observed over time.
Correlation analysis of prefrontal cortex by activity type (Connectivity)
This study conducted a connectivity analysis of the PFC subregions according to activity type (ICT vs. OGA) to evaluate the effects of each activity on cognitive function enhancement in elderly participants with dementia and cognitive impairment. The top left diagram in Fig. 4 visually represents the PFC connectivity in the ICT group, while the top right diagram shows the PFC connectivity in the OGA group. The heat maps on the bottom left and right illustrate the correlation coefficients between the various PFC subregions in the ICT and OGA groups, respectively. The analysis of PFC connectivity in the ICT group revealed generally weak connectivity. The highest connectivity was observed between the left LPFC and right LPFC, with a correlation coefficient of 0.3. Overall, the ICT group exhibited low connectivity strength, indicating limited interaction between different PFC regions. In contrast, the OGA group demonstrated significantly higher connectivity compared to the ICT group. Notably, there was strong connectivity between the left and right LPFC and LOFC in the OGA group, with correlation coefficients as high as 1.0, indicating very active interaction between these regions. The PFC connectivity in the OGA group was substantially higher and exhibited more complex interactions across various subregions compared to the ICT group.
Discussion
This study utilized NIRS to analyze PFC blood flow responses during two different cognitive enhancement activities, with the aim of demonstrating the effectiveness of gardening activities in reducing dementia symptoms and improving cognitive function in elderly individuals with dementia and cognitive impairment. The results showed that gardening activities significantly increased PFC blood flow in these individuals, making them more effective in providing cognitive stimulation and neural activation compared to the conventional cognitive enhancement training activity, ICT. Given the central role of the PFC in cognitive functions, its activation suggests that gardening can help alleviate dementia symptoms and mitigate cognitive decline or enhance daily life. These findings are consistent with previous studies that have demonstrated increased PFC blood flow and improved cognitive function following activities conducted in natural environments with dementia patients (Lee and Kim, 2008; Morita et al., 2017; Baek et al., 2022; Lentoor, 2024).
Previous studies that have examined the effects of nature-based activities, including gardening, on elderly individuals with dementia have reported that experiences in natural environments positively impact participants’ psychological and physiological health. In the study by Borella et al. (2023), significant increases in scores obtained from questionnaires assessing mental health and physical abilities after gardening activities confirmed the positive effects of gardening on cognitive function and physical capacity in dementia patients. Additionally, various activities in natural settings were shown to have positive effects on sleep and anxiety (Lee and Kim, 2008), as well as on psychological stability and stress reduction (Borella et al., 2023) in individuals with dementia. Notably, studies focusing on cerebral blood flow changes in dementia patients have verified the activation of the PFC and the enhancement of neuroplasticity through increased blood flow during nature-based activities. This was demonstrated using methods such as Brain-Derived Neurotrophic Factor (Ng et al., 2018; Park et al., 2019), Electroencephalography (Kim et al., 2021; Du et al., 2022), and Functional Magnetic Resonance Imaging (Lentoor, 2024). Thus, based on the findings of previous studies, the results of this study suggest that gardening activities conducted in natural environments can positively influence cerebral activation and emotional stability in elderly individuals with dementia and cognitive impairment. This supports the effectiveness of gardening activities as an intervention to alleviate and potentially prevent dementia symptoms.
Specifically, the consistent trend of increased blood flow observed in most PFC regions other than the left VLPFC and left LOFC during gardening activities in this study has several important implications for the cognitive function of elderly individuals with dementia. The right VLPFC and both DLPFCs play crucial roles in higher-order cognitive functions, such as working memory, problem-solving, and attention. The observed increase in blood flow in these areas suggests that the brain is allocating more resources to maintain or enhance cognitive functions (Pievani et al., 2014; Beishon et al., 2017). Furthermore, the increased blood flow in the right LOFC and FP-PFC indicates heightened emotional stability and social interaction (Bechara et al., 2000; Miller and Cohen, 2001; Goldman-Rakic, 2011; Yeo et al., 2018). In conclusion, the activation of the right VLPFC, bilateral DLPFCs, right LOFC, and FP-PFC suggests that gardening activities positively influence cognitive function, emotional stability, and social behavior in dementia patients, thereby activating various brain regions. These changes in blood flow reflect the brain’s complex adaptive mechanisms to slow the progression of dementia and maintain quality of life through the diverse environmental and physical stimuli provided by gardening activities.
In addition, this study found that gardening activities resulted in overall higher cerebral connectivity compared to ICT activities. Specifically, the strong connectivity observed between the left and right VLPFC and LOFC suggests that gardening activities promote interaction between various regions within the PFC. Previous research indicates that dementia patients often experience reduced connectivity between prefrontal regions, leading to impairments in information exchange, cognitive activity, and decision-making (Buckner et al., 2008; Kester and Scheltens, 2009). This reduction in interregional interaction is recognized as one of the key symptoms of dementia (Metzger et al., 2016). The high connectivity observed in the gardening group suggests a potential approach to mitigating these issues. The enhanced connectivity observed during gardening activities implies more active information processing and exchange within the PFC, which is directly associated with improvements in cognitive function (Buckner et al., 2008). The positive outcomes of gardening activities may be attributed to the healing effects of the natural environment, the sensory stimulation from interacting with natural elements, and the combination of multiple physical activities.
The natural environment facilitates the reduction of physiological stress and promotes emotional stability, which contribute to the activation of frontal lobe functions (Clatworthy et al., 2013; Soga et al., 2017; Kang et al., 2022; Youn et al., 2024). The reduction of the stress hormone cortisol, along with increased blood flow in the frontal lobe in elderly individuals with dementia, suggests that natural environments may contribute to enhancing frontal lobe functions through psychological stability (Han et al., 2018). Indeed, gardening activities provide physical stimuli during the process of planting and caring for plants, which can increase the necessary blood flow to the brain, and in turn strengthen PFC connectivity (Park et al., 2014; Lentoor, 2024). Kaplan and Kaplan (1989) argued that natural environments aid in attention restoration and cognitive rejuvenation. These effects may be particularly pronounced in dementia patients. While gardening activities take place in outdoor natural environments that offer these benefits, ICT activities are typically conducted indoors, where the healing effects of the natural environment may be more limited. The results of this study demonstrate that this environmental difference appears to have a direct impact on frontal lobe functions, with activities conducted in garden settings more effectively promoting PFC activation, which is particularly evident in dementia patients (Gonzalez and Kirkevold, 2014; Pasanen et al., 2018). Furthermore, natural environments provide additional advantages for frontal lobe activation by stimulating multiple senses. In natural environments, individuals are exposed to a variety of sensory stimuli: visually rich colors, the diverse scents of plants, the tactile sensation of soil and plants, and the sounds of wind and birds (Kaplan and Kaplan, 1989; Franco et al., 2017). These multisensory stimuli activate various brain regions and can significantly enhance cognitive functions and emotional regulation, particularly in the PFC (Lee, 2017; Jo et al., 2019).
Additionally, frontal lobe activation is closely linked to physical activity. The frontal lobe plays a critical role in cognitive function and emotional regulation, and its activation is enhanced by the increased blood flow resulting from physical activity (Park et al., 2014; Lentoor, 2024). Unlike ICT activities, which are primarily limited to small muscle stimulation, gardening activities involve various forms of physical activity, such as planting and moving soil. These activities engage both large and small muscle groups, including the upper (arms) and lower (legs) limbs, promoting overall blood circulation throughout the body and particularly enhancing frontal lobe activation (Park et al., 2014). Research has shown that physical activity increases brain plasticity and strengthens neural connections, thereby improving cognitive function (Lentoor, 2024). For elderly individuals with dementia and cognitive impairments, regular physical activity can play a crucial role in preventing frontal lobe degeneration and enhancing cognitive resilience (Erickson et al., 2011). The increased blood flow stimulated by physical activity delivers more oxygen and nutrients to the brain, further enhancing frontal lobe function. In this context, gardening activities offer cognitive stimulation beyond mere physical activity, suggesting that activities in natural environments may be effective in preventing dementia and improving cognitive function. The more pronounced increase in blood flow observed in gardening activities compared to ICT activities in this study likely reflects the combined effects of the environment, sensory stimulation, and physical activity.
Most studies on gardening activities to date have focused on healthy individuals, finding that gardening reduces frontal lobe blood flow, leading to stress reduction and emotional stability (Toyoda et al., 2017; Park et al., 2019; Lee et al., 2021; Lai et al., 2023). In contrast, this study, conducted with elderly individuals with dementia, found that gardening activities led to an increase in frontal lobe blood flow among participants. As dementia progresses, there is a gradual loss of neurons in the frontal lobe, leading to a reduction in oxygen and nutrient supply, and consequently, a decrease in blood flow (Pievani et al., 2014; Beishon et al., 2017). This reduction in blood flow diminishes metabolic activity in the frontal lobe, which in turn leads to a decline in frontal lobe function (Maillet and Rajah, 2013). In elderly individuals with dementia, the activation of the frontal lobe is closely related to improvements in cognitive function, and an increase in blood flow to the frontal lobe reflects such activation (Beishon et al., 2017). In contrast, healthy adults do not experience such structural damage in the PFC, allowing their blood flow responses to remain stable, with the brain’s vasculature functioning normally to provide adequate blood flow to the PFC (Lu et al., 2011). Thus, changes in frontal lobe blood flow may vary depending on the individual’s health status and cognitive demands, and understanding the differences between elderly individuals with dementia and healthy adults requires careful consideration of each subject’s structural and functional brain characteristics.
Thus, this study suggests that gardening activities may be more effective than indoor cognitive training in increasing frontal lobe blood flow and enhancing cognitive function in elderly individuals with dementia and cognitive impairments. The findings demonstrate that gardening contributes to the activation of the frontal lobe through various environmental, sensory, and physical stimuli. The high connectivity observed within the frontal lobe suggests that these activities play a crucial role that goes beyond mere cognitive stimulation, potentially enhancing overall brain function. This enhanced connectivity may improve cognitive judgment and emotional stability in dementia patients, ultimately contributing to better quality of life and slowing disease progression. Therefore, gardening activities can be considered a meaningful intervention method in the care of individuals with dementia.
However, the observed decrease in blood flow in the left VLPFC and left LOFC requires further investigation. These regions are closely related to emotional regulation, and the reduction in blood flow may represent a positive response, where excessive activation diminishes as dementia patients find emotional stability in stressful situations (Beishon et al., 2017). Conversely, this decrease could also indicate a decline in emotional function or the onset of negative outcomes such as depression. This could lead to a weakening of emotional regulation abilities, suggesting that additional emotional support might be necessary. Further research is required to provide a clear interpretation of these findings. Although this study examined the short-term effects, additional investigation is needed to understand the impact of repeated gardening activities on frontal lobe function.
Conclusion
This study confirmed that gardening activities can provide significant short-term improvements in frontal lobe function for elderly individuals with dementia and cognitive impairments. Through an analysis of prefrontal cortex blood flow using near-infrared spectroscopy (NIRS), it was empirically demonstrated that gardening activities increase frontal lobe blood flow more effectively than indoor cognitive training activities, thereby inducing cognitive stimulation and neural activation, and ultimately improving cognitive function. Notably, blood flow changes were most pronounced in the dorsolateral prefrontal cortex (DLPFC), ventrolateral prefrontal cortex (VLPFC), lateral orbitofrontal cortex (LOFC), and frontopolar prefrontal cortex (FP-PFC). The observed increases in blood flow across most frontal lobe regions suggest a normalization of impaired frontal lobe function in elderly individuals with dementia and cognitive impairments. Furthermore, the study found that sustained changes in blood flow over time, along with enhanced interregional connectivity post-activity, indicate that gardening activities promote interaction within the prefrontal cortex. These findings suggest that gardening activities may be effective in activating brain functions in elderly individuals with dementia and cognitive impairments. However, the observed decrease in blood flow in the left VLPFC and LOFC requires further investigation to determine whether this is a positive or negative response. In conclusion, this study confirms that gardening activities can significantly improve short-term frontal lobe function in elderly individuals with dementia and cognitive impairments, demonstrating the effectiveness of nature-based activities as an intervention for enhancing cognitive function and emotional stability in dementia patients. Future research should seek to validate these effects through a variety of activities.
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