Center for Environmental Neuroscience
Director: Simone Kühn
Research Questions
Organizing Research Principle
Advancing Theory in the Field
Neuroscientific research on brain plasticity has convincingly demonstrated that activities and experiences shape both the function and the structure of the adult human brain. Plenty of evidence has proven the effects of lifestyle factors such as physical exercise, eating habits, alcohol consumption, and smoking. Targeted interventions such as cognitive training have been shown to cause measurable changes in brain function and structure. However, to date neuroscience has treated the human brain as if it exists in a petri dish. In reality, humans are surrounded by and embedded in different physical, social, and cultural environments. This oversight is especially striking given that neural plasticity was first discovered in an animal research context, in which the physical living environments of rodents were deliberately manipulated. Scientists observed that, in comparison to a standard condition, mature animals housed in so-called "enriched environments" displayed neurogenesis: the advent of new neurons. What, then, would an enriched environment for humans—one that improves the neuroplasticity of the brain—look like? It is surprising that this vital research question has scarcely been addressed. In view of the multitude of environmental problems the planet is currently facing, from climate change and the destruction of habitats to urbanization and pollution, a better understanding of the effects of the physical environment on the individual is urgently needed.
Research Questions
Existing epidemiological research in the field of psychiatry has demonstrated that the physical environment is closely linked to mental health outcomes. Numerous studies have contrasted the prevalence of psychiatric disease in people living in urban versus rural areas and observed overall that multiple mental disorders are more frequent in urban than rural populations. Interestingly, psychiatry has focused closely on the potentially harmful effects of urban living, whereas environmental psychology has stressed the beneficial effects of contact to nature. CEN, which opened in July 2024 out of the Lise Meitner Group for Environmental Neuroscience (2019–2024), and the new research field of environmental neuroscience (Kühn, 2024) aim to integrate and synergize previous research from psychiatry and environmental psychology by unraveling the underlying mechanisms through which the physical environment influences mental health, including affective, behavioral, and cognitive dimensions. The declared goal of CEN is to open the black box between the physical environment and mental health, as shown in Figure 1. This black box represents at least three major research questions (Kühn & Gallinat, 2024).
1. What are the "active ingredients" of the physical environment that elicit positive mental health effects (e.g., green color, air pollutants, soundscapes, terpenes)? Previous research has oftentimes relied on summary categories comparing urban versus rural living, or different countries; CEN's goal is to define exactly which features of the physical environment are at the core of the observed effects.
2. Relatedly, what are the major human sensory pathways via which these active ingredients are perceived? For instance, is visual input from a natural environment sufficient to improve well-being, or is the interaction of multiple sensory systems, consisting for example of visual, auditory, and olfactory input, more effective?
3. Which precise neural mechanisms are involved in processing the physical environment and resultant mental states? This third facet of the black box will help to uncover whether the salutogenic effects of the natural environment are primarily driven by cognitive or affective pathways.
This mechanistic approach links the emerging field of environmental neuroscience to classical theories from environmental psychology that have long debated whether the restorative effects of nature are primarily grounded in recovery from stress (Stress Recovery Theory [SRT]; Ulrich et al., 1991) or in restoration from attentional fatigue (Attention Restoration Theory [ART]; Kaplan & Kaplan, 1989). Building on these theories, neuroscientific evidence can be used to test which brain networks—cognitive or affective—are in fact more strongly involved in the processing of natural environments.
CEN aims to advance a more holistic understanding of the environment as a complex, multi-dimensional phenomenon. This will enable the field to identify the "active ingredients" of the physical environment that positively impact the brain and mental health, thereby mapping the pathways and mechanisms by which the physical environment affects the brain and mental health.
Key References
CEN's Organizing Research Principle: Levels of Inference Across Different Time Spans
To unravel how the physical environment impacts mental health, research at CEN deliberately covers different levels of inference and different time spans. The levels of inference range from observational/correlational to interventional/causal and mechanistic approaches (see Figure 2). At the same time, the studies span different time scales, from the investigation of long-term effects (in the range of years to months), e.g. of the living environments at and around the home address, to short-term effects (in the range of weeks to hours), e.g., holidays or visits, such as a walk or extended stay in a particular setting, to momentary and immediate effects (in the range of minutes to seconds).
The funnel in Figure 2 illustrates CEN's organizing research principle, which aims to successively reduce the number of potential environmental factors as research moves from observational/correlational, through interventional/causal to mechanistic levels. The physical environment consists of multi-faceted, highly complex, and likely interacting factors. By utilizing large-scale observational studies, very comprehensive lists of environmental variables can be screened to determine the most relevant potential "active ingredients," which can then be more directly investigated in short-term studies to establish causal relationships and immediate exposure studies that provide insights into potential mechanisms.
On the upper level of the funnel, CEN mainly utilizes existing large-scale neuroimaging datasets (e.g., Berlin Aging Study II (BASE-II), Hamburg City Health Study (HCHS), IMAGEN, the German National Cohort study (NAKO), the UK Biobank) in which participants' address history data can be used to characterize their living environments, thanks to geographic information systems (GIS) approaches that enable a precise characterization of potentially relevant environmental features (e.g., air and noise pollution, tree cover density). This observational/correlational approach guides the search for relevant potential active ingredients; however, it can only statistically control for potential confounders such as socio-economic status or lifestyle factors such as exercise or nutrition. To better control for such confounders, the twin study design comes into play.
Although still observational in nature, the twin study design, especially the comparison of monozygotic twins who live in separate environments, enables researchers to relate differences in the physical living environment to within-pair brain and mental health differences, while controlling for genetics and a multitude of additional shared factors in the living environment during upbringing. To facilitate this, in 2022, CEN founded the first German twin registry, GERTRUD. Using GERTRUD, CEN researchers have conducted a first neuroimaging twin study to investigate for which environmental factors an association with brain and mental health persists after controlling for genetic confounding. The goal is to use these well-controlled analyses to further refine the number of relevant active ingredients previously identified in studies on the long-term effects, which are then further targeted in studies investigating short-term exposures in real-life contexts and immediate exposures in the lab.
To investigate the effects of short-term environmental exposures on brain structure and function, CEN established a micro-longitudinal study paradigm precisely to capture day-to-day variability in environmental exposures, as well as in brain and mental health parameters. In the first "Day2Day" study (Filevich et al., 2017), which pioneered the paradigm, the focus was on identifying lifestyle factors—measured 24 h before magnetic resonance imaging (MRI) acquisition—that explain variability in brain measures to enable better control of those confounding variables in future studies. In the follow-up study, Day2Day Environment (ongoing), the goal is to quantify the physical environments that surround participants in the 24 hours before MRI acquisition using GPS tracking. This will enable researchers to identify associations between short-term environmental exposures and brain structure and function.
The "walk out" intervention study paradigm was established to measure short-term effects as a randomized-controlled trial in which participants are assessed in the lab before and after a randomly assigned exposure to a walk in different physical environments, e.g., a forest or an urban street (Sudimac & Kühn, 2022, 2024; Sudimac et al., 2022). To widen the scope of potential environments that can potentially be studied within this paradigm, in the future CEN plans to use a newly acquired mobile 1.5 T MRI scanner for studies in the field. This will further facilitate the measurement of short-term effects of environmental exposure onto the brain and mental health.
At the lowest level of the funnel (see Figure 2), CEN conducts experimental lab studies to disentangle how specific constituents of complex environmental exposures act on mental health. Methods such as virtual reality (VR) are used, sometimes combined with MRI or functional near infrared spectroscopy (fNIRS), to capture the acute processes at play during environmental exposure, for instance, by investigating the supra-additive effects of different sensory modalities in a forest exposure setting. In this context, CEN also aims to understand the origin of environmental preferences. Biophilia theories posit an innate, evolutionary tendency in humans to seek connection with nature and other forms of life. These theories assume that this preference has an evolutionary basis. If there were such a basis for nature preference, it should be detectable across the lifespan, and vitally, already in infancy and early childhood. To examine this, CEN has re-established a baby lab at the MPIB, where researchers investigate the supposed universal preference for visual depictions of natural environments.
Another topic CEN addresses within the scope of immediate effects of environmental exposures is the indoors. Although most of the research in the fields of environmental psychology and neuroscience contrasts exposure to rural versus urban environments, the time human beings actually spend outdoors is limited (on average, only 10–20% of their day). Therefore, research at CEN aims to unpack how acute exposure to indoor environments, mostly presented virtually, influences mental and brain health.
Key References
Advancing Theory in the Field
To provide an overview of the present state of evidence in the field of environmental neuroscience using MRI, Beyer et al. (2024) performed a scoping review gathering and summarizing the currently available results in the book "Environmental Neuroscience" (Kühn, 2024). In the field of architectural neuroscience, Tawil and Kühn (2026) compiled an overview of the current evidence for potential benefits and preferences for curvatures in indoor environments for the "Routledge Handbook of Neuroscience and the Built Environment."
In a recent perspective paper, CEN—together with co-authors–proposed a conceptual framework on person–environment fit (Kandler et al., 2024), postulating that it arises through three mechanisms: attraction to compatible environments, construction of new environments, and conformation to existing ones. Furthermore, the framework suggests a distinction between subjective fit (perceived match) and objective fit (independently measured match), linking good fit to positive outcomes like well-being and satisfaction and misfit to stress and negative health impacts.
With the goal to better understand the consistency of beneficial or detrimental effects of rural compared to urban living on humans, CEN conducted a review synthesizing findings from 500 studies (Prugger, Sztuka, & Kühn, ongoing) covering domains such as mental and physical health, cognition, personality, brain function, and epigenetics. An interesting geographical gradient of the direction of reported findings was discovered, namely that in studies from the Global North, urban living is linked to increased risks for mental disorder, whereas rural living is frequently associated with higher quality of life. This stands in stark contrast to studies from the Global South, where urban environments are positively associated with mental health benefits, likely due to better healthcare access.
Finally, CEN contributes to theoretical advances in the fields of environmental psychology and neuroscience by introducing a novel approach to generate and test new theoretical directions using grounded theory (Glaser & Strauss, 1967). This research methodology, which is usually applied to qualitative data, inductively develops theories from collected data. Instead of prematurely establishing rigid hypotheses, grounded theory proposes a flexible process in which insights emerge directly from data and are continually tested. Researchers use an iterative process of simultaneous data collection and analysis, applying the constant comparative method to ensure the emerging theory is firmly "grounded" in empirical evidence. CEN shifts this approach to quantitative data, treating separate studies as distinct data points that are aggregated according to different coding schemes to expand the view of the field and existing data in a bottom-up approach. In a first application, CEN questioned the long-held assumption in environmental psychology that the positive effects of nature exposure are restorative, i.e., that they arise when participants are in a deficient state (e.g., stressed or anxious) and nature exposure alleviates this deficit state (Figure 3). Many existing studies implement an experimental paradigm in which participants are first exposed to stress and then to nature. Interestingly, the results of CEN's ongoing grounded-theory meta-analytical approach suggest considerable evidence for the existence of nature's instorative effects, namely for the positive consequences of nature even when participants were not in a state of deficit prior to exposure (Prugger & Kühn, ongoing). This has important implications for the field and beyond, suggesting that nature exposure could be utilized for preventive purposes. As soon as CEN and the growing field of environmental neuroscience has accumulated sufficient observational/correlational evidence on the effects of long-term exposures spanning different geographical regions as well as periods across the lifespan, CEN is planning to use this grounded-theory meta-analytical approach to develop a theoretical framework of how the environment acts on mental and brain health that is empirically grounded.
Key References