Hypothesis

Claim: Age‑related over‑consolidation of the vocal fold lamina propria not only stiffens the tissue but also dampens mechanosensory feedback from fibroblasts to the recurrent laryngeal nerve, leading to maladaptive central motor silencing that manifests as presbyphonia.

Mechanistic chain:

1. Elevated L‑type calcium channel (CACNA1S) activity → ↑ collagen I/III deposition & ↓ MMP activity → increased ECM stiffness.
2. Stiff ECM alters integrin‑FAK‑YAP/TAZ signaling in fibroblasts, suppressing Piezo2‑mediated stretch‑activated ATP release.
3. Reduced fibroblast‑derived ATP lowers P2X3/P2X2 receptor activation on afferent nerve endings, decreasing firing rates.
4. Diminished afferent input shifts the sensorimotor balance toward reliance on predictive internal models, causing cortical sensorimotor areas (vocal motor cortex, SMA) to down‑weight error signals — analogous to neural dedifferentiation in aging brains.
5. The result is a voice motor system that is overly confident in its prior predictions, resisting vocal‑effort updates and producing reduced pitch range, increased phonatory threshold pressure, and perceived fatigue.

Testable predictions:

• In aged rats, verapamil treatment will reduce collagen content and increase MMP‑1/‑8 (as shown previously) and restore Piezo2‑dependent ATP release from vocal fold fibroblasts.
• Piezo2 knock‑down in fibroblasts will abolish the verapamil‑induced increase in afferent firing and prevent improvement in vocal motor learning tasks, despite ECM softening.
• Acute optogenetic stimulation of Piezo2‑positive fibroblasts in aged animals will mimic verapamil’s effect on afferent firing and improve voice outcomes without altering collagen levels.
• Functional MRI (or calcium imaging) of vocal motor cortex will show decreased dedifferentiation (increased network specialization) after verapamil only when Piezo2 is intact.

Falsification: If verapamil improves vocal biomechanics and voice performance in aged animals without any change in Piezo2‑dependent ATP release or afferent firing, or if Piezo2 loss does not block the behavioral rescue, then the proposed mechanosensory‑feedback mechanism is not necessary, falsifying the hypothesis.

References (inline): Increased collagen I/III synthesis with decreased elastin in aging vocal folds[https://pmc.ncbi.nlm.nih.gov/articles/PMC9948577/]; Calcium channel upregulation drives collagen production in aging vocal fold lamina propria[https://pmc.ncbi.nlm.nih.gov/articles/PMC6834399/]; Verapamil reverses this by reducing collagen and increasing MMP-1/-8 degradative enzymes in aged vocal fold fibroblasts[https://pmc.ncbi.nlm.nih.gov/articles/PMC6834399/]; Age-related shifts in small leucine-rich proteoglycans[https://pubmed.ncbi.nlm.nih.gov/39665313/]; Neural dedifferentiation and reduced network specialization[https://pmc.ncbi.nlm.nih.gov/articles/PMC6635135/]; Older adults' memory consolidation relies on increased competition between resting-state networks[https://www.frontiersin.org/journals/aging-neuroscience/articles/10.3389/fnagi.2014.00344/full]; Neural dedifferentiation stems from multiple distinct mechanisms[https://news.utdallas.edu/health-medicine/neural-dedifferentiation-2024/].