Memory & focus

The whole apparatus of thinking: taking information in, holding it, working with it, and getting it back out. It is not one faculty but at least six, and they decline at different rates and respond to different things — which is why they are split.

Training load increases it.

Meta-analyses of RCTs show exercise improves cognitive function in older adults (PMC9858649); in mild cognitive impairment, 26 RCTs (2,085 participants) gave a large effect on global cognition (SMD 0.81, 95% CI 0.58-1.05) (PMC12753406). Exercise->mood rests on SMD -0.61 across 79,551 participants. EXERCISE->cognition does not come close: an umbrella review re-estimating 24 meta-analyses (109 primary studies meeting criteria) found a small median effect size d = 0.17 (95% CI 0.13-0.19) with substantial heterogeneity (I-squared 43.4 percent) — and reported that all but two primary studies used underpowered designs to detect an effect that small. That re-estimation is a preprint (biorxiv 2022.02.15.480508), so it is not relied on as the verifying source; it is shown because a null-leaning finding should not be suppressed for being inconvenient. The peer-reviewed support is J Affect Disord 2024 (umbrella review of exercise on depressive symptoms and cognitive function). The honest statement: the direction holds; the magnitude is small and the primary literature is underpowered for it. PMC9858649

Protein quality control increases it.

Hartl 2011, Nature 475:324 — an age-related decline in proteostasis capacity permits the protein-aggregation diseases (Alzheimer's, Parkinson's), tying proteostasis to cognitive integrity. doi 10.1038/nature10317

Cell turnover reduces it.

Apoptosis-in-AD review 2001, J Neural Transm — massive neuronal death by apoptosis is a common feature of neurodegenerative-disease brains; apoptotic neuronal loss in Alzheimer's drives the cognitive decline of dementia. PMID 11227497

Nerve insulation increases it.

Fields 2008, Trends Neurosci — myelin regulates the velocity and synchrony of axonal conduction between cortical regions, supporting information processing, learning and cognition. PMC2486416

Memory chemical increases it.

Bartus 1982, Science 217:408 — the cholinergic hypothesis: acetylcholine signaling underpins memory; its loss drives cognitive decline. PMID 7046051. Causal in humans, not just correlational: cholinergic antagonists impair memory in animals and humans; scopolamine given to neurosurgical patients during a memory task disrupted the amplitude and timing of hippocampal theta oscillations. Reversible lesion: cholinergic hypofunction from 192-IgG-saporin cut hippocampal Arc and BDNF and worsened spatial acquisition — and GALANTAMINE reversed both the deficit and the Arc/BDNF levels (PMID 20865740). The therapy limit is explicit: a practice-guideline update found NO level a evidence that cholinesterase inhibitors give symptomatic improvement at the MCI stage, while donepezil benefits more severe AD. And the effect is phase-specific: scopolamine disrupted memory encoding, with retrieval a separate question. PMID 7046051

Brain inflammation reduces it.

Depression neuroinflammation review 2025 — microglial cytokines impair hippocampal neurogenesis and synaptic function, producing cognitive deficits. PMID 40305200. The claim is supported, by a different paper: Int J Mol Sci 2025;26(15):7212 (doi 10.3390/ijms26157212, PMID 40806341) -- persistent microglial activation leads to chronic neuroinflammation which alters neuronal signaling pathways, resulting in accelerated cognitive decline, with PI3K identified as the driver connecting inflammation to neurodegeneration. Verified at source against the correct paper. doi 10.3390/ijms26157212 · PMID 40305200

Supports BDNF signaling increases it.

Alonso 2002, Hippocampus 12:551 — hippocampal BDNF is required for short- and long-term memory formation. PMID 12201640. Separately, BDNF in the dentate gyrus is required for consolidation of pattern-separation memory (Bekinschtein 2013). It is a two-way relationship, not a one-way arrow: BDNF increases the density of alpha-7 nicotinic receptors on hippocampal neurons, and activation of those same receptors upregulates BDNF — acetylcholine and BDNF regulate each other. rodent lesion work; human BDNF evidence is peripheral serum, a proxy for a central process. PMID 12201640

New neuron growth increases it.

Shors 2001, Nature 410:372 — reducing adult hippocampal neurogenesis impairs trace-memory formation. PMID 11268214. Adult hippocampal neurogenesis is exquisitely sensitive to neuronal activity, and post-mortem human studies (Boldrini 2018; Moreno-Jimenez 2019) report neurogenesis persisting throughout adult life with a progressive and significant decline in Alzheimer's patients. Whether adult humans make new hippocampal neurons at all is one of the most contested questions in Neuroscience — the review's own phrasing that recent studies 'have confirmed the existence' concedes that it was in doubt, and other post-mortem work has reached the opposite conclusion. The rodent evidence is not disputed; the human translation is. Acetylcholine is among the signals regulating it, tying this edge to the Cholinergic → Cognition link. PMID 11268214

Body clock increases it.

Different studies indicated that chronic jet LAG influences the elevated level of cortisol, poor cognitive functions, low working memory, learning problems, and higher rates of breast and prostate cancer. Corroborated at review level: disturbances in circadian rhythms ARE associated with mood and cognitive disorders. Weaker than the four edges drawn alongside it: those rest on controlled laboratory separation of misalignment from sleep restriction; this one rests on chronic-jet-lag observational work in which the two are confounded. Drawn, but at a lower grade, and the confound is the reason. doi 10.37349/emed.2022.00093 · PMC12529610

Calm under stress reduces it.

Meta-analysis of nine prospective cohorts, 29,608 participants: prevalent anxiety at baseline confers 24 percent higher risk of all-cause dementia. And the authors do the most useful thing a paper can do with a small effect - they size it against known risk factors: despite this being considered a low effect size, with an average of 20 percent of people with anxiety, the proportion of incident dementia attributable to anxiety is estimated to be 4 percent - comparable to diabetes at 3.2 percent and hypertension at 5.1 percent. A modest relative risk in a very common exposure outweighs a large relative risk in a rare one. And the conditional carries something this pathway uniquely has: two opposite interaction results. For cardiovascular disease, anxiety acts independently of depression - very little evidence of multiplicative OR additive interaction across 431,973 people. For type 2 diabetes, anxiety alone did nothing - risk appeared only in anxiety-insomnia comorbidity (HR 1.40) and not with each disorder separately. Same exposure, two companions, opposite structures. Anyone modeling anxiety as a uniform risk multiplier is wrong in one of those two directions. The authors call anxiety a potentially modifiable risk factor and note the results ARE still controversial. Observational throughout, and reverse causation is a live concern for dementia in particular, where prodromal anxiety may be an early symptom rather than a cause. doi 10.3390/jcm9061791 · PMC10377450

Brain adaptability increases it.

Synaptic plasticity is a well-established mechanism supporting learning and memory across the lifespan, and cognitive functions such as memory, processing speed and executive function commonly decline, driven largely by changes in neuroplasticity mechanisms. Anything sold on “growing new brain cells” is selling the rodent result. Synaptic plasticity is the human mechanism; neurogenesis is not established in adult humans. doi 10.1007/s10522-025-10300-4 · PMC6685093

Insulin sensitivity increases it.

Brain insulin resistance sits at the CROSSROAD between metabolic and neurodegenerative disease. Insulin acts on the hippocampus, a brain area playing a pivotal role in learning and memory and primarily affected in Alzheimer’s disease. A named molecular step: insulin induces phosphorylation of GSK3-beta on the inhibitory serine 9 residue, thus reducing its enzymatic activity. doi 10.1007/s10522-025-10300-4 · PMC6685093

Lowers cortisol reduces it.

Chronic activation of the HPA axis disrupts homeostatic mechanisms, leading to structural and functional alterations in brain regions such as the prefrontal cortex, hippocampus, and amygdala — mediated by glucocorticoid exposure, neuroinflammation, and neurotransmitter imbalances, strongly correlated with cognitive decline. The reviewers note early objective detection remains limited by the subjective nature of psychological assessments. doi 10.1007/s10522-025-10300-4 · PMC6685093

Oxidative stress reduces it.

Named among the core mechanisms across six reviews of cognitive aging and synaptic plasticity: neurotransmitter systems, calcium signaling, neurotrophic support, cellular signaling pathways, and neuroinflammation, oxidative stress, and vascular integrity, all of which redirect the trajectory of synaptic failure associated with cognitive decline in aging. doi 10.1007/s10522-025-10300-4 · PMC6685093

It increases Mood.

10.3389/fpsyt.2021.577058 — Cognitive decline and mood are documented as co-traveling, and the Mood (Positive Affect) → Cognition link is already drawn on the RR 1.66 Alzheimer's figure. This is the reverse arm on weaker evidence - the forward direction has the meta-analytic evidence. This link rests on the reviews of this outcome as a whole, and no effect size specific to it has been reported. doi 10.3389/fpsyt.2021.577058

It reduces Calm under stress.

PMC12583720 — This is what the symptom costs rather than what it causes physiologically. It is shown at reduced weight because no separate effect size has been reported for this arm. The asymmetry is deliberate and stated. Cognitive difficulty and anxiety co-travel; the Anxiety → Cognition link is drawn on the 24 percent dementia-risk figure, so this is the weaker return arm. PMC12583720

It increases Training load.

PMC4034407 — 10.3389/fnhum.2014.01044 — low - executive function governs adherence to any behavioral intervention, and exercise touches 13 outcomes here. doi 10.3389/fnhum.2014.01044 · PMC4034407

It increases Sleep.

10.1093/sleepadvances/zpad016 — low - cognitive state and sleep quality co-travel; the forward arm the Sleep → Cognition link is better evidenced. doi 10.1093/sleepadvances/zpad016

It reduces Calm pain signaling.

The defining feature is that the pain is real and the tissue is not damaged: central sensitization manifests as hyperalgesia, allodynia, expanded receptive fields, and impaired endogenous pain inhibition, and in osteoarthritis the same phenomenon does not correlate with radiographic findings - severe pain may persist despite stable joint structure. The mechanism is a balance failure in both directions at once: in the dorsal horn there is excessive release of glutamate, ATP, and substance P, leading to activation of NMDA receptors - while at the same time descending inhibitory mechanisms, notably those mediated by GABA, ARE weakened. Too much excitation and too little inhibition. And mast cells carry a specific hypothesis: thalamic mast cells releasing histamine, IL-1-beta, IL-6, TNF, CGRP and substance P, either stimulating thalamic nociceptive neurons directly or via microglia. Stated by the authors as a hypothesis, not an established mechanism. The reviewers ARE blunt about the state of knowledge: the pathophysiology and etiopathogenesis remain largely unknown, and there is NO definitive pathogenesis except for altered central pain pathways. doi 10.3390/biomedicines12071543 · PMC6687840

It increases Balance & falls.

10.20900/agmr20240002 — Drawn from reviews of neighboring outcomes rather than from studies of this outcome itself, which is weaker evidence, and the map marks it so. Verbatim: “Cognitive impairment (CI) increases an individual's risk of falls due to the role cognition plays in gait control”. doi 10.20900/agmr20240002 · PMC8665555

It increases Living independently.

41439004 — Major neurocognitive disorder is diagnosed when cognitive decline interferes with independence in everyday activities; the DSM-5 functional criterion was revised so the threshold emphasizes loss of independence in daily living. Sachdev 2014, Nat Rev Neurol 10:634-642 — Classifying neurocognitive disorders: the DSM-5 approach. doi 10.1038/nrneurol.2014.181

It increases Body awareness.

Interoception is a measured subdomain of the cognition domain. doi 10.1016/j.neuroimage.2018.12.037 · PMC11645458

Autonomous (Executive Command) →

Nebula (Warrior Mode Rocket Fuel) →

Senolytic (Senescent Zombie Cell Clearance) →

ALZ (Memory Preservation) →