Squeaky Shoes and Brain Aging: Friction Physics Meet Human Hippocampal Neurogenesis in Aging

This Nature podcast features two science stories: first, researchers explain why squeaks occur when rubber patterns slide on hard surfaces, showing that tiny contact geometry details at the interface set the pitch of the squeak; second, scientists discuss a Nature paper arguing that adult human hippocampal neurogenesis exists and changes with cognitive function in aging, including a resilient signature in super agers and implications for therapies. The episode includes demonstrations with a simple setup to visualize friction pulses and interviews with authors Adele Jaloli and Gabrielle Albertini, and Orli Lazarov discussing the potential for pharmacological modulation of neurogenesis.

Introduction and two scientific threads

The Nature podcast presents two intertwined stories in this episode. The first centers on a curious everyday phenomenon: squeaking shoes. Researchers describe how a soft material gliding over a hard surface produces squeaks, a sound tied to a well-defined physical mechanism. The second thread examines a debated process in the human brain, hippocampal neurogenesis, and how its presence and dynamics may relate to aging and cognitive function. The show stitches together experiments, expert commentary, and implications for future work, highlighting how basic physics can illuminate everyday experiences and how brain plasticity might influence aging trajectories.

Two prominent teams anchor the physics story. Adel Jaloli from Harvard and Gabrielle Albertini from the University of Nottingham discuss how patterns on rubber blocks and a controlled sliding system reveal that geometry at the contact interface shapes the sound. Meanwhile, Ali Lazarov from the University of Illinois, Chicago, leads a study suggesting that human hippocampal neurogenesis exists and varies with cognitive status across aging cohorts, including exceptionally high neurogenesis in super agers and very low levels in preclinical Alzheimer’s disease. The conversation touches on mechanisms, data interpretation, and the potential translational implications for aging and cognition.

Friction, patterning, and the squeak

The squeaking phenomenon arises when a soft surface slides over a hard one. The researchers design a simple system in which rubber blocks with ridges slide across an acrylic plate, illuminated by LEDs and recorded with a high-speed camera. The main discovery is that geometry matters. Small details at the interface determine the spectral content of the sound. When ridged rubber is used, the pulses at the interface become channelled, producing a single dominant pitch and harmonics reminiscent of a musical note. Without the ridges, opening pulses travel in multiple directions, generating a noisier, less musical sound. The team also finds that the pitch is robust to changes in pressure, although higher pressure can influence how opening pulses initiate.

To illustrate the practical side of the science, the researchers demonstrate the Imperial March using blocks of different heights, showing that height controls pitch and that the approach is reproducible even outside the lab where precise torques and angles are hard to control. The broader implication is that micro-geometric features at contact interfaces can control frictional acoustics, with potential applications in engineering, earthquake science, and metamaterials design. A quote from the segment captures the core idea: "The main discovery is that geometry matters. Small details matter in friction."

“The main discovery is that geometry matters. Small details matter in friction.” - Nature researchers

Hippocampal neurogenesis and aging

The neuroscience thread centers on a debate about whether neurons continue to be born in the adult human hippocampus and how neurogenesis relates to cognition across aging. Ali Lazarov describes a developmental trajectory from neural stem cells to immature neurons in the hippocampus, and notes the substantial neurogenesis observed in young adults. The team then applies the signature to older cohorts with differing cognitive function: a pre-clinical Alzheimer’s group, a diagnosed Alzheimer’s group, aging individuals with preserved cognition, and a group termed super agers with exceptional memory performance. The results show markedly reduced neurogenesis in the disease cohorts but an elevated, distinct signature in super agers, suggesting a resilience mechanism linked to epigenetic alterations that modulate gene expression.

Looking ahead, the researchers discuss functional validation using patient-derived induced pluripotent stem cells (iPSCs) to test whether manipulating the identified gene signatures can influence cognitive outcomes. They acknowledge limitations inherent to postmortem tissue and emphasize the need for live-brain tracking technologies to map neurogenesis over time. The discussion frames a potential therapeutic avenue: if the signature can be functionally validated, it may be possible to pharmacologically induce neurogenesis and slow cognitive aging, though careful validation and safety checks are required before any clinical application.

“Hippocampal neurogenesis is probably one of the most profound forms of plasticity, and many studies in rodents and in primates have shown that hippocampal neurogenesis plays different roles in learning and memory.” - Ali Lazarov, University of Illinois, Chicago

“If we're able to validate the signature functionally and show that indeed it does regulate cognitive function, the goal would be to develop therapies that would allow us to induce these processes pharmacologically.” - Ali Lazarov, University of Illinois, Chicago

Implications, limitations, and future directions

The show closes by addressing limitations in the hippocampal study, notably that postmortem tissue provides only a single time point, making it difficult to track disease progression. Despite this, Lazarov argues that the study presents a thorough analysis linking neurogenesis to cognitive function and aging, offering a potential path toward therapies that enhance neurogenesis while acknowledging the need for further validation and live-brain data. The episode ends with a forward-looking tone, underscoring the ongoing quest to connect basic neuroscience with practical interventions that support healthy brain aging.

“Postmortem tissue is one point in time following death, so it's definitely limiting our capability to follow neurogenesis over time.” - Ali Lazarov, University of Illinois, Chicago