High-resolution MRI and the Functional Architecture of the Human Medial Temporal Lobe
We are interested in the functional architecture of cognitive functions with a particular focus on memory and the human medial temporal lobe. Characterizing these functional networks in detail in the first place is crucial to understand the effects of Alzheimer’s disease pathology. Thus, we investigate which brain regions and networks are involved in specific memory and other cognitive processes. For example, how our brain can manage to separate very similar experiences without confusing them in memory (Berron et al., JNeurosci, 2016) or how different anatomical pathways are involved in cognitive processing of different material (Berron et al., Neurobiol Aging, 2018).
To that end we primarily use high-resolution structural and functional MRI at 3T and 7T to investigate the differential functional connectivity profile as well as the differential involvement of various functional brain networks (Berron et al., Neurobiol Aging, 2018, Berron, Vieweg et al., NeuroImage: Clinical, 2017; Maass, Berron, eLife, 2015).
Effects of Alzheimer’s Disease Pathology on Medial Temporal and Neocortical Memory Systems
Domain-specific medial temporal lobe pathways support different types of human memory. While brain regions in an anterior-temporal network are more involved in memory for objects, brain regions in a posterior-medial network are preferentially associated with memory for spatial scenes (Berron et al., Neurobiol Aging, 2018). Interestingly, these networks overlap with Alzheimer’s disease pathology in different disease stages. Recently, we could characterize the sequence and dynamics of accumulation of tau pathology across human memory networks using tau PET imaging (Berron et al., Brain, 2021) highlighting that brain areas in the anterior temporal lobe show the earliest signs of tau accumulation.
Using functional MRI, biomarkers for Alzheimer’s disease pathology and novel cognitive paradigms, we aim to characterize AD-related changes in functional connectivity as well as in task related activity to define disease stage-specific imaging markers and to understand the origin of early impairment of cognition and memory pathways (Berron et al., JNeurosci, 2019). Recently, we could identify the early changes in MTL-cortical functional connectivity in Alzheimer’s disease, again highlighting the earliest signs of AD-related disconnection in the anterior-temporal network (Berron et al., Brain, 2020).
Spatial distribution patterns of Alzheimer’s disease pathology as well as its consequences that can be observed using brain imaging suggest stage- and subtype-specific cognitive impairment in Alzheimer’s disease. Our aim is to understand the earliest cognitive impairment, the sequence of cognitive changes as well as individual cognitive trajectories. To that end, we have developed memory tasks that rely on brain regions that are early affected by Alzheimer’s disease pathology. However, memory performance shows considerable variability across individuals and is influenced by many additional factors that make it difficult to rely on a single test session. Thus, we use smartphone-based assessments which allow for repeated and longitudinal testing of specific memory functions in a remote and unsupervised setting. Recent results from a Citizen Science project within Germany highlight the feasibility and potential of such approaches. Using these techniques, we investigate individual trajectories of memory decline in early stages of Alzheimer’s disease using biomarkers for Alzheimer’s disease pathology based on positron emission tomography (PET), cerebrospinal fluid (CSF) and blood plasma.
Subregions in the medial temporal lobe are critically involved in human episodic memory. Recent research showed that subregions are differentially involved in specific memory processes and functions. In order to assess structure-function relationships between the volume and thickness of MTL subregions on one side and specific memory functions on the other, but also to investigate their specific activity profile, regions-of-interest by means of anatomical masks are necessary. Therefore, we developed a manual segmentation protocol for MTL subregions together with colleagues from the DZNE in Magdeburg and collaborators at the University of Pennsylvania and the Allen Institute for Brain Science in Seattle. However, in order to be able to better interpret research on MTL subregions across studies, we are part of the Hippocampal Subfields Group to harmonize segmentation protocols across research labs.