The rationale for the study grows out of two accelerating global trends: urbanization and climate change. As more people crowd into cities and as heat, air quality, and noise conditions become less stable, understanding how these exposures affect the brain becomes a matter of public health, not just academic curiosity. Previous environmental neuroscience research has tended to focus either on long-term factors, such as the greenness of a neighborhood measured over years, or on isolated single exposures like particulate matter concentration. What has been largely neglected, the authors argue, is the interplay between multiple exposures encountered in everyday life and the consequences of their short-term fluctuation. A person might spend Monday in a quiet park-rich district and Tuesday stuck in traffic on a noisy, polluted arterial road. Conventional study designs average such variation away; the Day2Day Environment project is built specifically to capture it.

Methodologically, the study is remarkable for its density. Thirty participants are being followed across 25 testing sessions, a design that falls into the category researchers call dense longitudinal sampling. Instead of measuring each person twice, a year apart, the team samples each individual repeatedly over a compressed timeframe, which makes it possible to model how within-person changes track environmental changes. This approach contrasts sharply with the typical two-wave cohort study, where any observed brain difference could reflect countless unmeasured confounds. With 25 repeated observations per participant, the researchers can separate stable between-person differences from dynamic within-person dynamics, an analytical advantage that has become increasingly valued in psychology and neuroscience over the past decade.

The environmental side of the data collection relies on a combination of wearable devices, geographic ecological momentary assessments, and GPS-based geospatial tracking. Wearable sensors log physiological and behavioral variables continuously, including physical activity and, through the momentary assessment surveys delivered in geographic context, subjective states such as stress and affect. The GPS stream allows each participant’s movement through the city to be reconstructed, so that self-reported experiences can be anchored to specific locations and times. Crucially, the protocol explicitly targets air quality, noise, and light exposure, three environmental dimensions that are rarely measured simultaneously in the same individuals. By stacking these layers on top of each other, the project creates a moment-by-moment portrait of each participant’s exposure landscape, something that a single stationary monitoring station or a satellite-based estimate of neighborhood greenness cannot provide.

On the brain side, the neuroimaging program is unusually comprehensive for a study with this many repeated sessions. Each participant undergoes magnetic resonance imaging that includes T1-weighted and T2-weighted images collected both at rest and during cognitive tasks. T1-weighted structural images provide the standard measure of brain anatomy, allowing researchers to quantify cortical thickness, volume, and surface morphology across sessions. T2-weighted images are sensitive to aspects of tissue iron content and microstructure and are also the workhorse sequences for functional MRI, so collecting them across rest and task states gives the team windows into both brain structure and brain function over time. The inclusion of task-based imaging is particularly noteworthy, since it allows the investigators to ask not just whether the brain changes, but whether environmental exposures alter how the brain performs work in the scanner.

Beyond these core sequences, the protocol incorporates quantitative multi-parameter mapping, a family of quantitative MRI techniques that estimate tissue properties such as magnetization transfer saturation, proton density, and relaxation times rather than relying on image intensities that can shift between scanners and sessions. Because the same participants return to the same scanner 25 times, quantitative measures offer a way to detect subtle biological change with greater specificity than conventional structural imaging. In addition, the team acquires high-resolution proton density images focused on the hippocampus, a structure central to memory and one of the few brain regions where adult neurogenesis and environmental sensitivity have been extensively debated. The hippocampus has repeatedly been implicated in environmental neuroscience, from studies of exercise to studies of urban stress, so dedicating high-resolution imaging resources to this structure signals a clear a priori hypothesis about where short-term environmental effects might be detectable. Diffusion tensor imaging rounds out the battery, providing measures of white matter microstructure by quantifying the directional diffusion of water molecules along axonal pathways.

The behavioral and psychological measurements are designed to complement the imaging rather than merely accompany it. Repeated assessments of cognition and affect collected in daily life allow the researchers to test whether environmental fluctuations predict momentary changes in mood, stress, or cognitive performance, and whether those changes in turn relate to neural measures. This layered design means the dataset can speak to questions at multiple timescales: how a noisy commute affects an afternoon, how a week of poor air quality relates to that month’s brain measures, and how all of these short-term dynamics might accumulate over the course of the study. The combination also opens the door to studying short-term neuroplasticity, the capacity of the adult brain to change its structure and function over days and weeks, in response to the dynamic interplay of multiple environmental exposures rather than a single manipulated variable.

The project is anchored at the Max Planck Dahlem Campus of Cognition in Berlin, where the MRI team and student research assistants carried out the demanding logistics of data collection, and it is funded by the Max Planck Society and the European Union through a European Research Council Consolidator Grant awarded to Simone Kühn, whose prior work has examined how urban environments and housing conditions relate to brain structure. The study received ethics approval from the Local Psychological Ethical Committee at the Center for Psychosocial Medicine at University Medical Center Hamburg-Eppendorf, and all participants provide written informed consent and receive monetary compensation. The authors note that the dataset’s diversity of measurements may prove valuable for research questions extending well beyond environmental neuroscience, since repeated multimodal sampling of the same individuals is a scarce and precious resource for methodologists testing new analytical tools, reliability estimates, and models of within-person dynamics.

What makes the protocol scientifically exciting, and likely to generate attention well beyond specialist circles, is its implicit reframing of the environment as a fast-moving variable rather than a static backdrop. If measurable neural signatures can be linked to day-to-day environmental variability, the implications extend to urban planning, public health policy, and even individual lifestyle choices, suggesting that the conditions people encounter on a Tuesday afternoon might matter for the brain in ways that annual averages conceal. Of course, a protocol paper describes a study in progress rather than results, and the thirty-participant sample is small, meaning findings will need replication and careful interpretation before any policy conclusions are drawn. Yet the design itself represents a methodological milestone: by fusing wearable sensing, geospatial tracking, momentary self-report, and a state-of-the-art multimodal MRI battery within a single dense longitudinal framework, the Day2Day Environment project offers the research community both a template and a richly annotated dataset for probing one of the most intimate and consequential questions in modern neuroscience, namely how the shifting character of our daily surroundings becomes biology inside our heads.

Subject of Research: Effects of daily variations in environmental exposure on human brain structure and function

Article Title: Investigating effects of day-to-day variations in environmental exposure on the human brain: study protocol for the Day2Day Environment project

Article References: Falkenstein, K., Pauley, C., & Kühn, S. (2026). Investigating effects of day-to-day variations in environmental exposure on the human brain: study protocol for the Day2Day Environment project. BMC Neuroscience, 27(1), Article 38. https://doi.org/10.1186/s12868-026-01052-z

Image Credits: AI Generated

DOI: 10.1186/s12868-026-01052-z

Keywords: environmental neuroscience, brain structure, brain function, MRI, wearable sensors, GPS tracking, ecological momentary assessment, air quality, noise exposure, light exposure, hippocampus, longitudinal study