Hypothesis: Age‑dependent decoupling of amygdala‑vPFC structural connectivity gates the impact of CRF hypersensitivity on fear extinction and trait anxiety

Core claim With advancing age, declining structural connectivity between the amygdala and ventral prefrontal cortex (vPFC) reduces the transmission of bottom‑up CRF‑driven excitatory signals from the central amygdala (CeA) and bed nucleus of the stria terminalis (BNST) to prefrontal inhibitory circuits. Consequently, even though CRF‑expressing neurons become hypersensitive (as shown in early‑life pain and aging models), their ability to drive anxiety‑related output is attenuated, producing lower trait anxiety despite heightened intrinsic excitability. In younger adults, intact amygdala‑vPFC pathways allow CRF hypersensitivity to amplify fear responses and impair extinction via disrupted CRF‑GABA signaling in the BNST. Therefore, the protective effect of connectivity loss in aging is contingent on the integrity of CRF‑GABA microcircuits; when these circuits are compromised (e.g., by GABA(A)α1 loss in CRF neurons), the age‑related benefit disappears and anxiety rises.

Novel mechanistic insight We propose that the amygdala‑vPFC white‑matter tract acts as a gain controller for CRF signaling: high gain (young, strong connectivity) amplifies CRF‑induced amygdala output, driving anxiety and extinction failure; low gain (old, weakened connectivity) dampens this amplification, permitting compensatory prefrontal inhibition to dominate. This gain‑control model predicts that pharmacological reduction of CRF tone (CRF1 antagonists) will have age‑dependent efficacy: it will markedly reduce anxiety and rescue extinction in young subjects with high gain, but will show minimal additional benefit in older adults where gain is already low. Conversely, artificially boosting amygdala‑vPFC connectivity (e.g., with repetitive transcranial magnetic stimulation targeting the vPFC‑amygdala pathway) in older adults should reinstate the gain, making them sensitive to CRF1 blockade and revealing latent anxiety that is currently masked.

Testable predictions

1. In a cross‑sectional human sample (ages 20‑35 vs 65‑80), diffusion‑weighted imaging will show a negative correlation between amygdala‑vPFC fractional anisotropy and self‑reported trait anxiety only when CRF1 receptor availability (measured by PET with a CRF1 ligand) is high; when CRF1 availability is low, the correlation will flatten.
2. Administering a selective CRF1 antagonist (e.g., verucerfont) to young adults will reduce anxiety scores and improve fear‑extinction retention, with the magnitude of change positively correlated with baseline amygdala‑vPFC connectivity. The same drug in older adults will produce no significant change unless participants receive concurrent excitatory neuromodulation designed to increase amygdala‑vPFC connectivity.
3. In aged rats, chemogenetic enhancement of amygdala‑vPFC projections (via DREADDs) will reinstate anxiety‑like behaviors and extinction deficits that are reversible by CRF1 antagonism, demonstrating that the age‑related protection is connectivity‑dependent.
4. Conditional knockout of GABA(A)α1 receptors in CRF neurons of the BNST will abolish the age‑related anxiety benefit: aged mice with this manipulation will exhibit high anxiety despite low amygdala‑vPFC connectivity, confirming that intact CRF‑GABA inhibition is required for the gain‑control mechanism to operate.

Falsifiability If CRF1 antagonists reduce anxiety equally across age groups irrespective of amygdala‑vPFC connectivity, or if boosting connectivity in older adults fails to reinstate sensitivity to CRF1 blockade, the gain‑control hypothesis would be falsified. Likewise, if GABA(A)α1 deletion in BNST CRF neurons does not alter the anxiety‑connectivity relationship in aged animals, the proposed microcircuit dependency would be unsupported.

Implications This framework integrates structural disconnection, molecular hypersensitivity, and microcircuit inhibition to explain why anxiety traits can decline with age while underlying CRF systems remain sensitized. It also suggests that therapeutic strategies targeting CRF signaling should be stratified by age and prefrontal‑amygdala connectivity status, potentially rescuing extinction in younger patients while avoiding unnecessary pharmacotherapy in elders unless connectivity is first enhanced.