Hypothesis: Chronic type I interferon (IFN-I) signaling in the aging brain may underlie predictive over-consolidation—the shift from adaptive prediction to maladaptive pattern rigidity. I propose that IFN-I-mediated suppression of neural stem cell (NSC) activation and synaptic plasticity represents not merely a reduced neurogenic capacity, but an active enforcement of the brain's confidence in existing predictive models. This leads to specific predictions: (1) aged brains showing cognitive rigidity should display elevated IFN-I signatures in circuits most engaged in novel pattern learning, particularly the prefrontal cortex and hippocampal CA3, and (2) interventions introducing controlled uncertainty or prediction error—such as unexpected reward schedules, novel environment exposure, or pharmacologic manipulation of prediction error signaling—should transiently reduce IFN-I activity in these circuits, enabling plasticity reactivation.

Mechanistic Reasoning: The core idea here is "over-consolidation"—a system that has stopped tolerating surprise. The work shows that chronic IFN-I enforces NSC quiescence through Sox2 repression and mTOR/eIF2α modulation, locking cells into G0 arrest. Building on this, I suggest that IFN-I functions as a molecular confidence signal—when the brain's antiviral defense system becomes chronically activated by mitochondrial DNA release from aging microglia, it effectively tags the entire neural environment as "known and dangerous," suppressing the exploratory plasticity needed to update internal models. The JAK-STAT pathway thus implements a cost-benefit trade-off: increased defense (via ISG upregulation) at the expense of learning (through Sox2/BDNF suppression). This means the same molecular machinery protecting against pathogens actively degrades the capacity to encode novel, surprising information.

Testable Predictions: One prediction is that aged mice exhibiting high cognitive rigidity—assessed through reversal learning paradigms measuring tolerance for prediction error—will show elevated ISG expression specifically in prefrontal cortical layer 2/3 pyramidal neurons and hippocampal CA3 mossy cells, which are circuits critical for pattern separation and model updating. This should be compared to aged mice showing flexible learning. Another prediction is that repeated exposure to controlled uncertainty—variable reward locations in a spatial maze, for instance—will produce measurable reductions in ISG expression (Ifit3, Isg15) and restore Sox2/BDNF expression in the dentate gyrus subgranular zone, relative to aged mice in stable environments. A third prediction is that pharmacologic blockade of IFNAR1 combined with controlled uncertainty exposure will yield synergistic cognitive restoration beyond either intervention alone, since uncertainty removes the behavioral trigger for IFN-I upregulation while IFNAR1 blockade removes the molecular barrier to plasticity.

Falsifiability: This hypothesis would be falsified if aged brains with high cognitive rigidity show no correlation between ISG expression in prediction-circuit regions and behavioral inflexibility. It would also be falsified if controlled uncertainty exposure fails to alter IFN-I signaling in NSCs despite improving cognitive flexibility, indicating the mechanisms operate independently.

Synthesis: Bringing together the over-consolidation framework with IFN-I biology reveals cognitive aging not as simple decay but as a hyper-confident immune-metabolic state. The intervention implication is significant: we may not need to "restore" plasticity but rather provide the uncertain signals the aging brain has become too rigid to generate itself, while simultaneously removing the IFN-I gate that blocks the plastic response to that uncertainty.