Magnetic resonance elastography, or MRE, works by vibrating tissue gently and imaging the shear waves that ripple through it. The wave patterns are then fed through an inversion algorithm that reconstructs the tissue’s viscoelastic properties, most commonly reported as shear stiffness, a measure of resistance to deformation, and damping ratio, which reflects the relative viscosity of the tissue, or how much mechanical energy it absorbs. Because the technique is entirely non-invasive, it can be applied to living human brains repeatedly across the lifespan. The resulting measures are thought to emerge from the combined biomechanical characteristics of neurons, glia, myelin, vasculature, and the extracellular matrix, along with how those components are organized in tissue. One of the most robust findings in the entire brain MRE literature is year-over-year decline in global brain stiffness with aging, on the order of 0.3 to 1.0 percent per year depending on region, and recent machine learning brain-age models that incorporate MRE data show improved performance over those built from volume and diffusion measures alone.

The most striking discovery, however, is that regional brain mechanics correlate with cognition. In a landmark series of studies, researchers found that hippocampal damping ratio in young adults was strongly associated with relational memory performance on a spatial reconstruction task, while hippocampal volume was not, suggesting that MRE captures microstructural information relevant to memory that conventional imaging misses. The finding replicated in larger samples and extended to other hippocampal-dependent tasks. High-resolution work examining individual hippocampal subfields later showed that in adults spanning ages 23 to 81, subfield stiffness, rather than damping ratio, predicted memory performance, with different subfields correlating with different memory tasks in ways consistent with their regional functional specialization. The story extends well beyond the hippocampus: damping ratio of the orbitofrontal cortex tracks performance on a fluid intelligence task, and studies have documented a double dissociation in which hippocampal mechanics relate to relational memory while prefrontal mechanics relate to rule learning, measured from a single task. Regional structure-function links have now been reported for sequence learning in older adults, vocabulary in children, and even risk-taking tendencies in adolescents.

Yet a puzzle sits at the center of this literature. Stiffness and damping ratio are not interchangeable. Stiffness is thought to be governed primarily by the density and organization of load-bearing structural elements, including neuron number, glial cell density, and extracellular matrix composition. Damping ratio reflects the balance between viscous and elastic behavior and is often interpreted as a signature of the organization and complexity of brain microstructure. A process that preferentially disrupts oligodendrocytes and myelination might affect damping ratio more strongly, while one characterized by edema or neuroinflammation might shift stiffness more prominently. The parameter that carries the structure-function association can shift with brain region, task, and the age of the population, which complicates any simple account. And the central question remains unanswered: which cells and matrix constituents actually generate the mechanical signal that MRE measures, and which of them link mechanics to cognition? That question cannot be resolved with in vivo human studies.

This is where rodents enter. Preclinical MRE in rodents pairs non-invasive in vivo imaging with direct histological, molecular, and genetic interrogation of the very same tissue, and it allows experimenters to perturb brain structure and function in controlled ways. The technique is well established in small animals and has already been applied productively to disease models. In mouse models of Alzheimer’s and Parkinson’s disease, MRE reveals regional softening generally consistent with human findings, associated with amyloid deposition, dopaminergic neurodegeneration, and tissue remodeling. In a cuprizone-induced demyelination model of multiple sclerosis, MRE captured reduced stiffness and damping ratio tied to myelin loss and oligodendrocyte death, while an experimental autoimmune encephalomyelitis model produced viscoelastic changes corresponding with inflammatory cell infiltration. Lesion-based studies have revealed localized remodeling of the extracellular matrix, particularly disruption of perineuronal nets, the specialized lattice structures that surround certain neurons. In a rat model of fetal alcohol spectrum disorders, the Delaware team found reduced brain stiffness consistent with disrupted perineuronal nets in adolescence that resolved by early adulthood.

What is missing, the researchers argue, is the healthy brain. Almost all rodent MRE work has focused on pathology, while the human MRE-cognition findings are concentrated in normal development, normal aging, and cognitive variation in otherwise-healthy people. No rodent study to date has paired MRE with behavioral testing to understand neural function in the non-diseased brain. There are encouraging early signs of what such studies could yield: in a longitudinal study of young mice, MRE captured regional patterns of stiffness and damping ratio change that correlated with a variety of proteins identified through mass spectrometry, hinting at multiple interrelated contributors to developing brain mechanics. And in a recent study from the Delaware group, hippocampal damping ratio in adult female rats increased between the proestrus and estrus phases of the estrous cycle, mirroring known hormone-driven changes in cellular architecture. Brain mechanics, it turns out, are not fixed properties but fluctuating ones, sensitive to nuances of endocrine state on timescales of days.

The proposed experimental framework rests on two pillars. The first is identifying the microstructural basis of MRE signals by pairing in vivo acquisitions with multimodal post-mortem analysis of the same tissue, including quantitative immunohistochemistry for cell-type-specific markers, electron microscopy for myelin sheath thickness, and matrix-specific stains. Because homogeneous cohorts of healthy rodents lack the variability needed to replicate cross-sectional human correlations, the researchers propose controlled interventions instead. Exercise and environmental enrichment, classic paradigms in rodent neuroscience, produce well-documented cellular consequences, including neurogenesis, angiogenesis, dendritic spine complexity, extracellular matrix remodeling, and myelination, each a plausible mechanical contributor. Graded exercise intensity permits dose-response testing, and longitudinal measurements against baseline allow within-animal statistics. For sharper selectivity, the toolkit extends to conditional knockouts of structural proteins, viral-vector-driven cell ablation, pharmacological matrix disruption with agents such as chondroitinase ABC for perineuronal net digestion, and controlled demyelination or neuroimmune upregulation, though the authors caution that disruptions must remain physiologically relevant to the healthy brain, since the microstructure-to-mechanics relationship is likely nonlinear.

The second pillar is behavior, and here the challenges are real. Human MRE-cognition studies typically pair a single scan with a brief testing session, treating performance as a stable trait. Rodent assays generally require days to weeks of training, an interval that itself involves aging, development, and experience-dependent tissue remodeling. One promising entry point is fear and operant conditioning, which engages focal hippocampal-amygdala-prefrontal circuits and, crucially, can be acquired within a single session, allowing learning and testing to be compared with a corresponding MRE scan at a single time point. Broader cognitive batteries spanning hippocampal-dependent tasks such as the Morris water maze and novel object recognition, and prefrontal-dependent tasks such as rule learning and attentional set-shifting, would test regional specificity and generalizability. Such studies could also reveal why some MRE-cognition relationships emerge in stiffness and others in damping ratio, a distinction that remains largely conjectural despite its importance for interpreting human data.

The deepest question is whether brain mechanics are purely structural or also dynamic on cognitive timescales. The cellular events of learning span an extraordinary range: matrix metalloproteinase-9 is released at potentiated synapses within minutes, astrocytic processes retract during memory consolidation, microglia prune synapses over days, and learning-dependent myelination and perineuronal net remodeling unfold across weeks. Each is a plausible mechanical contributor. Astrocytic Piezo1-mediated mechanosensing even suggests that tissue mechanics may actively drive functions like neurogenesis and spatial memory, rather than passively reflecting them. An emerging methodology, functional MRE, pushes to the shortest timescales by probing whether measured mechanical properties shift within seconds alongside blood oxygenation changes, potentially implicating immediate, reversible changes in vascular and cellular compliance. It remains at the proof-of-concept stage, but if validated, it would bracket the full temporal range over which brain mechanics and cognition may interact. The researchers’ case is ultimately a pragmatic one: rodent MRE has proven itself in disease, and by turning its attention to healthy development, aging, and behavior, it could finally explain why the brain’s softness, elasticity, and viscosity carry information about how well we think, remember, and learn, with implications ranging from earlier prediction of cognitive decline to new mechanistic targets for protecting the aging brain.

Subject of Research: Using rodent magnetic resonance elastography to identify the cellular mechanisms underlying the relationship between brain tissue mechanics and cognition

Article Title: Brain mechanics and cognition: the role of rodent MR elastography in identifying cellular mechanisms

Article References: Milbocker, K. A., Vander Wiele, S. S., & Johnson, C. L. (2026). Brain mechanics and cognition: the role of rodent MR elastography in identifying cellular mechanisms. Frontiers in Cognition, 5, Article 1943713. https://doi.org/10.3389/fcogn.2026.1943713

Image Credits: AI Generated

DOI: 10.3389/fcogn.2026.1943713

Keywords: magnetic resonance elastography, brain mechanics, cognition, memory, hippocampus, damping ratio, stiffness, rodent models, neurodegeneration, aging, perineuronal nets, mechanobiology