To our knowledge, this is the first epidemiological study to examine the associations between exposure to beautiful environments and neuroimaging measures. We found that older people with high subjective neighborhood beauty ratings had larger mOFC and insula volumes than those with low subjective neighborhood beauty ratings. We also found that the volumes of these brain regions were not associated with objective neighborhood beauty.
Subjective neighborhood beauty was positively associated with mOFC volume. This finding is in line with the results of fMRI studies of the experience of beauty.5,6,8−10 Neuroimaging studies have shown that the orbitofrontal cortex is a heterogeneous brain region with many functions, such as sensory integration, modulation of visceral reactions, and decision making in emotional and reward-related behaviors.21,22 In particular, the human orbitofrontal cortex has been linked to the subjective experience of pleasantness.21,22 A quantitative meta-analysis showed that subjective pleasantness ratings (mostly ratings of pleasantness, attractiveness, or beauty) were associated with mOFC activation.23 Because most people are exposed to their neighborhood environment in daily life, living in a beautiful environment may activate the mOFC, which leads to an increase in mOFC volume.
Subjective neighborhood beauty was also positively associated with insula volume, which is in line with previous findings on the experience of beauty.6,9 The insula plays a fundamental role in human emotional awareness and interoception.24,25 In addition, insular volume has been associated with well-being (personal growth, positive relations, and purpose in life).26 Therefore, large insula volume may be an indicator of greater self-awareness and a more developed sense of beauty.
Objectively measured neighborhood green spaces, blue spaces, and plant diversity were not associated with mOFC and insula volumes. One possible explanation is that these brain regions are involved in only subjective or emotional experiences and perceptions of beauty. In this study, objective neighborhood beauty was measured using several natural indicators. This was based on the fact that nature often contains intrinsically beautiful characteristics, such as the golden ratio and the Fibonacci sequence, which are aesthetically pleasing.15,16 However, such objective beauty does not take into account individual preferences.14 For example, some people prefer rural neighborhoods rich in nature, whereas others prefer urban neighborhoods that feature less nature. Such preferences may explain the discrepancy we identified in the associations of subjective and objective beauty with brain volume.
Objective neighborhood beauty may be associated with brain regions that were not investigated in this study. For instance, higher prefrontal cortex and premotor cortex volume in children was associated with neighborhood green spaces, as assessed by the NDVI.27 One study identified an association between reduced subgenual prefrontal cortex activity and walking in a natural environment compared with walking in an urban environment.28 Another possible explanation for the lack of association between objective beauty measures and brain volume is the distribution of the objective neighborhood variables. That the study area is completely surrounded by a rich natural environment may have hindered the detection of an association between objective neighborhood variables and neuroimaging measures.
Another reason for the discrepancy between subjective and objective beauty findings is that subjective beauty measures may capture non-natural factors such as landmarks. There are many shrines, museums, and community centers in our survey area where festivals and local events are held.29 Japanese people appreciate the beauty of highly functional utensils, as expressed in the Mingei or folk craft movement.30 Subjective beauty measures may reflect the beauty of local cultures. This view is supported by the finding that subjective neighborhood beauty was weakly correlated with objectively measured neighborhood green and blue spaces (all correlations were approximately 0.3). We found that childhood exposure to neighborhood nature was associated with subjective neighborhood beauty, indicating the importance of personal experiences to subjective beauty.6,7 Further research is needed on the determinants of subjective beauty.
This study had several limitations. First, subjective neighborhood beauty was assessed using a single-item scale, which has not been validated. However, we confirmed that participants who lived in Matsunoyama, which has many hot springs, is rich in nature, and is a popular tourist destination,29 rated their neighborhood as more beautiful than those who lived downtown. This suggests that the scale has some validity. However, this scale should be expanded by adding more items that measure subjective beauty, and its validity and reliability tested. Second, we could not assess causality because this was a cross-sectional study; we can only conclude that individuals with larger mOFC and insula volumes were more likely to report subjective neighborhood beauty. However, most participants had lived in the same location for over 30 years (since they were young), which suggests that accumulated neighborhood exposure may contribute to the development of brain volume in specific regions. Additionally, we excluded participants with a history of psychiatric disorders, which are associated with brain volume.31–35 Finally, it is difficult to generalize the findings to older adults in other areas because the subjective perception of neighborhood beauty may vary with culture.
In conclusion, we identified several brain regions associated with living in a subjectively beautiful environment. We were able to link aesthetic exposure to specific phenotypes using objectively measurable brain images, which adds quantitative data to the qualitative research findings in this area. Older people with high subjective ratings of neighborhood beauty had larger mOFC and insula volumes than those with low subjective ratings of neighborhood beauty. These brain regions were not associated with exposure to objective neighborhood beauty such as green spaces, blue spaces, and plant diversity. Future studies should investigate whether this association holds for other populations and other regions. Clarification of the association between neighborhood beauty and health would contribute to health-friendly city design.