Scientific State of the Field
The versioned model of what is understood about Alzheimer's & metabolic dysfunction — distinct from a summary because it separates accepted, uncertain, and contested models, and preserves disagreement rather than flattening it. This is Pass 4 of the Scientific State Compiler, versioned locally (Scientific Git-lite).
7
Accepted
4
Uncertain
3
Contested
3
Open conflicts
12
Open questions
Accepted models
CNS Insulin Receptor Expression & Peripheral Resistance Linkconf 0.95
Insulin receptors are widely expressed throughout the CNS (hippocampus, cortex); peripheral insulin resistance is consistently associated with reduced cerebral insulin signaling.
Midlife Insulin Resistance as AD Predictorconf 0.90
Midlife insulin resistance predicts later cognitive decline and increased Alzheimer's disease risk.
Exercise-Induced Cognitive & Metabolic Benefitsconf 0.95
Exercise improves peripheral insulin sensitivity and is consistently associated with better cognitive outcomes in aging populations; voluntary wheel running increases hippocampal insulin receptor signaling and enhances long-term potentiation.
Amyloid-Tau Cascade as Dominant AD Modelconf 0.90
The dominant model of Alzheimer's disease centers on amyloid-beta accumulation and downstream tau pathology.
Metabolic & Vascular Dysfunction in Early ADconf 0.85
Metabolic and vascular dysfunction are implicated as early contributors to Alzheimer's disease.
Neuroinflammation & Microglial Convergenceconf 0.90
Microglia respond to both amyloid and metabolic stress; chronic neuroinflammation is consistently observed in postmortem tissue.
Early AD Blood-Brain Barrier Dysfunctionconf 0.90
BBB dysfunction is recognized in early Alzheimer's disease, often preceding measurable cognitive symptoms.
Uncertain models
BBB Insulin Transport as Causal Relayconf 0.60
Causal direction between BBB transport failure and neuronal insulin resistance remains unresolved; animal models support bidirectional causality while human data are strictly correlational.
Synaptic Decline Preceding Overt BBB Failureconf 0.65
Whether early synaptic vulnerability is driven by intrinsic metabolic stress or soluble amyloid oligomers rather than solely by compromised insulin transport is unspecified.
Context-Dependent AMPK Cognitive Effectsconf 0.55
AMPK activation simultaneously improves cognition via autophagy and suppresses memory via inhibiting synaptic translation; the molecular threshold or regulatory node that flips this balance is unknown.
Exercise Protection Strictly Tied to Insulin Signalingconf 0.60
It remains unclear whether exercise-induced cognitive protection holds when insulin signaling is pharmacologically blocked or can be dissociated via alternative neurotrophic or vascular mechanisms.
Contested models — preserved disagreement
Primary Driver of Early AD
A: Amyloid-tau cascade initiates or is the primary pathological driver.
B: Metabolic/vascular dysfunction initiates or permissively enables amyloid toxicity.
status: unresolved
BBB Insulin Transport Causality
A: BBB insulin transport failure is the primary cause of neuronal insulin resistance.
B: BBB insulin transport failure is a secondary consequence of neuronal insulin resistance.
status: unresolved
AMPK Cognitive Outcomes
A: AMPK activation enhances cognition by promoting autophagy.
B: AMPK activation suppresses memory formation by inhibiting synaptic translation.
status: unresolved
Conflict ledger
Temporal hierarchy of AD drivers
⟶ Amyloid-tau cascade is the primary initiating pathway.
⟶ Metabolic/vascular dysfunction initiates or permissively enables the amyloid cascade.
resolution: none
BBB insulin transport failure
⟶ Acts as the primary cause of neuronal insulin resistance.
⟶ Acts as a secondary consequence of neuronal insulin resistance.
resolution: none
AMPK activation downstream effects
⟶ Promotes cognitive enhancement via autophagy.
⟶ Suppresses memory via inhibiting synaptic translation.
resolution: none
Open questions
- What is the temporal hierarchy between metabolic/vascular dysfunction and amyloid-beta accumulation in early Alzheimer's disease, and is metabolic failure a permissive prerequisite for amyloid-induced neurotoxicity?
- Which specific BBB cell type or molecular pathway (endothelial transcytosis failure, pericyte-mediated vascular dysregulation, or astrocytic endfoot signaling disruption) is the primary mediator of the causal relay from peripheral insulin resistance to hippocampal neuronal insulin resistance?
- Does exercise-induced cognitive protection strictly depend on cerebral insulin receptor signaling, or can it be dissociated from insulin pathways via alternative neurotrophic or vascular mechanisms?
- Is metabolic stress alone sufficient to drive the chronic neuroinflammatory microglial phenotype observed in Alzheimer's disease, independent of amyloid-beta deposition?
- What are the clinical trial outcomes of metabolic interventions (e.g., insulin sensitizers, ketogenic diets) on cognitive trajectories in early-stage Alzheimer's disease patients, and do they validate preclinical metabolic hypotheses?
- What is the dynamic relationship between tau pathology propagation and cerebral metabolic stress, and does tau accumulation amplify or buffer metabolic vulnerability in early Alzheimer's disease?
- Does synaptic decline in early Alzheimer's disease precede overt BBB failure because of intrinsic neuronal metabolic stress or soluble amyloid oligomer toxicity rather than compromised insulin transport?
- How do sex-specific differences in peripheral insulin resistance and BBB integrity modulate the risk, onset, and progression of Alzheimer's disease?
- Do neurotrophic factors (BDNF, IGF-1) mediate the vascular remodeling and insulin sensitization effects of exercise in the aging brain, and can their supplementation replicate exercise-induced cognitive benefits?
- What specific BBB cell types and tight junction proteins are most critically dysregulated in early Alzheimer's disease, and how do their failures differentially impact insulin transport versus general barrier integrity?
- Under what molecular, temporal, or neuronal context-dependent conditions does AMPK activation shift from promoting cognitive enhancement via autophagy to suppressing memory formation by inhibiting synaptic translation?
- How do AMPK and mTOR isoform expression patterns vary across brain regions, and does this regional specificity explain the divergent cognitive outcomes of metabolic interventions?
Silence summary
Critical gaps remain regarding specific BBB cell types (pericytes, astrocytic endfeet, tight junction proteins), tau pathology dynamics relative to metabolic stress, neurotrophic factor mediation (BDNF, IGF-1) of exercise-induced vascular remodeling, sex differences in insulin resistance and AD risk, AMPK/mTOR isoform specificity across brain regions, clinical trial outcomes for metabolic interventions in early-stage AD, and systemic inflammatory markers with gut-brain axis contributions.
Version history (Scientific Git)
v1scientific-state2026-07-22T20:46:41.730925+00:00
hash c88754d56c98ac9f
v2scientific-state2026-07-22T20:49:09.205648+00:00
hash bd692c8db287b7f1
accepted ? · uncertain ? · contested ? · conflicts ?
v2 is the result of a closing-loop iteration: an open question was turned into a new evidence source and re-compiled. The diff above is real.
Version 2026-07-22T20:49:09.203976+00:00. Source question-state: 2026-07-22T20:16:09.410880+00:00. Re-compiling with new sources yields a new versioned commit and a real diff.