Research Area 1: Georeferencing to Investigate Long-Term Effects of Outdoor Living Environments
Within the scope of this research area, we explore data from large existing magnetic resonance imaging (MRI) cohort studies that include information on the daily living environment of participants, either acquired by means of questionnaires or by means of address data that we then further process using Geographic Information Systems (GIS) methods to extract geographical information from the surroundings of the home. We started this on data of older adults from the Berlin Aging Study II (BASE-II; Kühn et al., 2017; Kühn, Düzel, et al., 2021) and adolescents from the European IMAGEN project (Kühn et al., 2020) and the Dutch prospective BIBO study (Kühn et al., in press).
We have recently continued this line of research using various large-scale data sets that have been acquired with a focus on neuroimaging data, including the UKBiobank (48,000 participants) and the Hamburg City Health Study (HCHS), a study I am involved with (Jagodzinski et al., 2020; Augustin et al., 2022). HCHS is the largest monocentric health study worldwide and will comprise 45,000 individuals (neuroimaging to be available on 8,000 of them) who will be extensively characterized with respect to health factors but also to their home and workspace environment. Moreover, we have started to analyze brain data from the German National Cohort Study (NAKO, with more than 30,000 participants). At present we are attempting to go beyond the cross-sectional correlation analyses by using follow-up assessments (in IMAGEN) to relate environmental changes to neural changes over time, an endeavor that is supported by an ERC Consolidator Grant that I received in early 2023.
Recently, we started to collaborate with the Max Planck Research Group iSearch (Azzura Ruggeri) in order to investigate whether the amount of green space around the home and school address is linked to active learning in children.
Research Area 2: Extreme Environments
A major challenge of the research topic of environmental neuroscience is that the physical environments of participants are difficult to manipulate and difficult to assign randomly. Therefore, we have started to study individuals who decide to spend periods of time in extreme environments (Stahn & Kühn, 2021). In collaboration with the Center for Space Medicine and Extreme Environments at Charité Universitätsmedizin Berlin and the University of Pennsylvania (Alexander Stahn), we are conducting studies in different human analog missions that simulate aspects of long-term space missions (Stahn & Kühn, 2021, 2022). For example, we had—and still have—the opportunity to acquire brain data of individuals before and after they overwintered in Antarctica (Stahn et al., 2019) or spent weeks to months in confinement-simulating missions to Mars. This includes bed-rest studies simulating microgravity (Friedl-Werner et al., 2020) and actual space flight missions, funded by Deutsches Zentrum für Luft- und Raumfahrt (DLR), European Space Agency (ESA), and National Aeronautics and Space Administration (NASA).
Likewise, we have received permission to test 16 mission members in the Human Exploration Research Analogue (HERA,) in Houston, and 20 astronauts and cosmonauts who will spend at least 6 months on the International Space Station (ISS) and are currently testing the effects of zero gravity on affect and cognitive functioning in parabolic flights (Stahn et al., 2020).
In a similar vein and funded by the German Research Foundation (DFG), we have started to conduct a study on prisoners in correctional facilities, namely the correctional facility Justizvollzugsanstalt Fuhlsbüttel, Hamburg. We acquire structural and functional brain data as well as cognitive and clinical mental health data at the beginning of investigative custody and then follow up with them 1 year later. We will then compare prisoners who were released after investigative custody with those who had to stay in prison. Furthermore, we assess a control group of participants who are on probation and not in prison within the year of interest. Prisons likewise constitute extreme environments, often with very limited access to nature. Potential long-term effects of this kind of detention on brain plasticity, as well as on cognition, are of high societal relevance and have not been investigated to date.
Research Area 3: Exposure to Specific Elements of Environments to Investigate the Acute Effects of Environmental Stimuli
Within the scope of this research area, we experimentally expose participants to real or virtual (multimodal) environments. We also attempt to dissect environments into their constituents perceived by different modalities by using images/videos of environments, sounds, or odors.
Previous studies have demonstrated that taking a walk in a natural landscape versus a city environment can lead to improvements in mental health outcomes such as mood and stress, and improvements in cognition, in particular in working memory and cognitive flexibility (McMahan & Estes, 2015; Stevenson et al., 2018). The aforementioned theories, ART and SRT, posit that nature has positive effects on human beings. SRT emphasizes that the beneficial effects are initially via affect, whereas ART assumes that the effects are brought about via cognitive processes, namely the restoration of directed attention.
To test these theories, our PhD student Sonja Sudimac used functional MRI (fMRI) to investigate whether beneficial effects of nature on subjective well-being and cognition are accompanied by activation in brain regions associated with stress and affect or by attentional cognitive processes. We randomly assigned adult participants to a one-hour walk in a forest (Berlin-Grunewald) or in the city (Schloßstraße in Berlin-Steglitz) (Figure 3) and observed a reduction in stress-related amygdala activity after the walk in nature (Sudimac & Kühn, 2022; Sudimac et al., 2022). In another study, our PhD student Emil Stobbe assessed the effects of urban (transportation sounds) versus natural (birdsong) soundscapes on depressivity, anxiety, and paranoia ratings in healthy participants (Stobbe et al., 2022), showing that listening to birdsong significantly reduces depressivity, anxiety, and paranoia. In a follow-up fMRI study, he investigates the neural mechanisms driving these effects.
In order to investigate the effects of day-to-day variability in exposure to physical environments and its effects on the brain, we used data from our previous Day2day study, in which a small number of participants were measured 40–50 times in the MRI scanner over 6 months. At each scanning occasion we assessed what participants did in the 24 hours before scanning, including what they ate, how much exercise they took, whether they spent time outdoors, etc. Using this data, we observed that spending time outdoors was positively associated with gray matter volume in dorsolateral prefrontal cortex and positive mood (Kühn, Mascherek et al., 2022). At present we are conducting a follow-up project in which we hope to gather more evidence on these short-term effects of environmental exposure. We plan to equip 30 participants with a variety of sensors (measuring light, air pollution, noise, and electrodermal activity) to investigate how the environmental exposure 24 hours before scanning impacts brain structure and function, and to invite each participant for 25 assessment sessions. This study will also be funded by a recently obtained ERC Consolidator Grant.
Moreover, we started additional projects investigating the acute effects of environmental exposure on brain function using functional near-infrared spectroscopy (fNIRS) in the field and in virtual reality (VR). Our goal is to conduct experiments in which we can systematically investigate which modalities, such as vision, audition, and olfaction, as well as which combinations of modalities, play the most prominent role in eliciting positive effects on affect and cognition during the perception of a particular environment (e.g., forest).
Furthermore, we recently initiated a study in collaboration with Frederik Schröer from the Center for the History of Emotions, exploring to what extent the perception of forest pictures and the concept of the forest is linked not only to positive affect but also to anxiety.
Research Area 4: Architecture and Interiors
Since humans in developed countries spend almost 80–90% of their time indoors on average, we also focus on investigating the influence of interior design on humans. For example, we are examining the influence of sharp and curved shapes, ceiling height, and room size on affect and cognition as well as on underlying brain functioning. For this purpose, we make use of virtual reality (VR) technology, since it can generate a strong feeling of presence and so-called immersion effects and enables us to place participants in completely different environments. Moreover, VR allows us to systematically manipulate distinct aspects of the environment.
We have recently finished a study in which we compared rooms with curvilinear versus rectilinear interior design including furniture, carpets, lamps, and paintings. Our PhD student Nour Tawil, who is an architect by training, designed the VR rooms. In her first study, she was able to show that an exposure to curvilinear versus rectilinear interior design in 3D-VR revealed no differences in terms of preference, affect, and cognitive functioning (Tawil et al., 2021). However, in an online study where participants were shown 2D pictures, she observed more beneficial explicit ratings of beauty, liking, and stress for the curvilinear condition (Tawil et al., 2022). Currently, we are following up on these findings with implicit tests, assessing the tendency to approach/avoid the 2D pictures and attention biases. We are planning to continue this research by utilizing our means to project VR environments into the MRI scanner to investigate whether curvilinear rooms are related to approach-related brain activation whereas rectilinear interiors are associated with avoidance-related brain activation.
In addition, we have conducted rating studies using photographs of house facades. To our surprise, we found that the face-likeness of facades, which has been reported as relevant in the previous literature, was not a central rating dimension for our participants from Germany, Denmark, and Canada (Roessler et al., 2022). This research is currently being followed up using eye-tracking methodology and labelling of the architectural elements of the house facades.
On this project we work in close collaboration with architects from the Bauhaus-Universität Weimar (Prof. Dr. Jasper Cepl), the University of Cottbus (Prof. Dr. Nina Gribat; joint DFG grant for the development of a research network), and Prof. Dr. Anna-Maria Meister, who was recently granted a Lise Meitner Group that will be located at the MPI for Art History in Florence, Italy, as well as with the Academy of Neuroscience for Architecture (ANFA).
Research Area 5: Computer Science Methods in Environmental Neuroscience
The computer sciences have developed powerful tools to manipulate photographs and to help quantify information from images. Within this research area, we utilize this knowledge and attempt to apply it to relevant questions within the environmental neurosciences. One example is knowledge obtained in the field of computer vision for the analysis of GIS quantifications. Another area that we started to look into with our computer science master’s student Kira Pohlmann is the use of generative adversarial networks (GANs) to generate new pictures of house facades. As conditional GANs have been shown to accurately extract class-specific features, also in the context of architecture (Bachl & Ferreira, 2020), we trained a GAN conditionally on an image dataset containing 2,000 frontal views of detached houses. We asked participants to rate those houses on psychological dimensions such as homeliness, invitingness, relaxation, and safety. Based on those ratings we saw that the GAN achieved high accuracy in predicting how the generated images were rated by participants on psychological dimensions (Figure 4). The GAN can be utilized to generate extreme cases of what participants perceive as homely, for example, and therefore provide an interesting way to illustrate the results of our findings. We plan to use this methodology in the future to apply it to the generation of natural or urban scenes.
Moreover, we have started to use computer vision approaches to segment Google Street View images to characterize not only how much green space is accessible in a certain geographical region, but how much green can be seen from a first-person perspective of someone who is actually present at this location. This will also enable us to quantify constructs that have been largely neglected in related fields so far, such as the amount of visible sky (Sztuka et al., 2022). We have started to collaborate on the latter topic with Prof. Dr. Berndt Schiele, who is the director of the Center for Computer Vision at the MPI for Informatics in Saarbrücken.
Research Area 6: Twin Studies
In this research area, we have started to utilize the twin study design to mimic environmental neuroscientific research from the animal research domain in which typically genetically identical animals are randomly allocated to different environments and the effects on brain health are studied. The closest we can get to mimicking this design in humans is to recruit monozygotic twins (MZ) that have left their shared parental home environment and now live in different physical environments (discordant MZ twin design). This constitutes an ideal test bed to investigate the association between the physical environment and brain structure, brain function, and mental health in the absence of genetical confounders. For this reason, we are currently recruiting participants from the TwinLife project, inviting them to an extensive assessment of their residential history and their current physical environment, including a 1-week ecological momentary assessment and a brain imaging session. This study is funded by a grant from the Strategic Innovation Fund of the Max Planck Society and will be conducted in collaboration with Prof. Dr. Elisabeth Binder from the MPI for Psychiatry in Munich, who will support us in exploring epigenetic changes in relation to the within-pair differences in the physical environment.
Moreover, we have recently initiated a Germany-wide collaboration of twin researchers with the goal of creating a German twin registry analogous to existing registries in Australia, the Netherlands, and Sweden (involving Prof. Dr. Jan Beucke, MSH Medical School Hamburg; Prof. Dr. Martin Diewald and Dr. Bastian Mönkediek, Bielefeld University; Prof. Dr. Paul Enck and Prof. Dr. Andreas Stengel, University of Tübingen; Prof. Dr. Christian Kandler, University of Bremen; Prof. Dr. Frank Spinath, Saarland University; Prof. Dr. Fredrik Ullén, MPI for Empirical Aesthetics). The GerTRuD: German Twin Registry under Development will be located at the MPI for Human Development and will be based on the Castellum participant data base that has been developed on site.
Summary and Potential Impact
By providing a better understanding and quantification of the relationship between outdoor and indoor environments and the brain, we hope to make an impact on the design of physical environments, urban planning, and architecture in ways that will optimize well-being and cognitive functioning as well as the mental and physical health of society at large. With our work we hope to consolidate the emerging field of environmental neuroscience and inform the field of neuroscience in general regarding which environmental variables play a major role in brain plasticity.
Last but not least, our hope is that by elucidating individuals’ dependency on a beneficial physical environment, we can contribute to kick-starting the pro-environmental behavior on the part of each and every one of us that is urgently needed to save our planet.