Hypothesis

Age‑related interoceptive decline results from excessive stabilization of von Economo neuron (VEN) ensembles in the anterior insular cortex, where increased perineuronal net (PNN) density limits acetylcholine spillover needed for prediction‑error signaling, while concurrent myelin thinning slows signal propagation. Together these changes produce an over‑confident interoceptive map that suppresses surprise and reduces behavioral flexibility.

Mechanistic Rationale

PNNs form a dense extracellular matrix that hinders diffusion of neuromodulators and restricts spine turnover [1][3]. In VEN‑rich insular zones, this matrix likely curtails the brief acetylcholine surges that signal unexpected visceral input, shifting the cost‑benefit balance toward model stability [4]. Myelin thinning, rather than over‑stabilization, adds conduction delays and temporal jitter that degrade the precise timing of interoceptive bursts [6]. The combined effect is a network that treats noisy bodily signals as predictable, thereby lowering interoceptive accuracy and increasing reliance on entrenched priors.

Experimental Design

1. Subjects: Aged (24‑month) male and female mice; young (3‑month) controls.
2. Interventions:
   • Chondroitinase ABC digestion of hippocampal‑insular PNNs to reduce rigidity.
   • Intermittent hypoxia (10% O₂, 3 h/day, 5 days) to boost MMP‑9 activity and soften PNNs.
   • Clemastine treatment to promote remyelination as a structural control.
3. Readouts:
   • PNN density via WFA staining in insular VEN layers (co‑localized with FOXP2) [5].
   • VEN activation measured by c‑Fos after visceral challenge (e.g., intraperitoneal lactate).
   • Interoceptive accuracy assessed using a heartbeat‑detection analog (lick‑rate shifts to cardiac‑linked optogenetic pulses).
   • Myelin integrity evaluated by g‑ratio and MBP staining [6].
4. Control: MMP inhibitor (SB‑3CT) co‑administered with intermittent hypoxia to test dependence on matrix remodeling.

Predictions and Falsifiability

• If PNN reduction restores interoceptive accuracy despite persistent myelin thinning, the hypothesis is supported.
• If intermittent hypoxia improves accuracy only when PNNs are degraded (blocked by SB‑3CT), it confirms that matrix softening, not metabolic change alone, drives the effect.
• If remyelination alone fails to improve accuracy without PNN modulation, it indicates that rigidity, not just structural decay, limits interoceptive flexibility.
• Failure of these manipulations to alter interoceptive performance would falsify the claim that VEN‑centric PNN over‑consolidation is a primary driver of age‑related interoceptive rigidity.

This framework links extracellular matrix dynamics to the specific computational role of VENs in interoceptive prediction, offering a testable route to re‑introduce controlled uncertainty into an over‑consolidated aging brain.