Accelerate Learning & Increase Cognitive Capacity | Dr. Tommy Wood

Why does it matter? Because the advice telling you to avoid cortisol and seek flow is working against your brain

Dr. Tommy Wood — neuroscientist, University of Washington researcher, and competing natural strongman — arrives with data that cuts directly against the dominant wellness consensus on exercise, learning, and supplementation. The cortisol spike everyone's managing down is the exact signal that locks in hippocampal protection. The flow state everyone's chasing turns out to be the wrong target for actually getting better at a skill.

• Six months of Norwegian 4×4 HIIT preserved hippocampal structure on MRI five full years after the training ended — outperforming Zone 2 — and harder effort with more cortisol meant greater brain benefit • Cardio and resistance training protect entirely different brain structures through different molecular mechanisms; neither covers the brain's full structural needs • The clutch state — performing well while it still feels like hard cognitive work — is where neuroplasticity actually happens; flow is what you get years later as its expression • Omega-3s and B vitamins each fail separately; at least three RCTs now show they only slow cognitive decline when taken together

Six months of hard HIIT protected hippocampal structure for five years — and the cortisol spike was the mechanism, not the side effect

The more cortisol released during a workout, the greater the hippocampal protection. That's not a footnote — it's the central finding of an RCT that directly contradicts the wellness-culture consensus about high-intensity exercise.

The study randomized older adults across three groups: a low-intensity control, a Zone 2 treadmill group training three times a week, and a group doing the Norwegian 4×4 protocol — four minutes at 85–95% of maximum heart rate, three-minute rest, repeated four times, three sessions per week for six months. Both the Zone 2 and HIIT groups improved their VO2 max similarly. But on hippocampal structure measured by MRI, the HIIT group wasn't just better — it was in a different category. And when researchers followed up five years after the six-month intervention had ended, that structural benefit had held.

The mechanism Wood points to is lactate. High-intensity work floods the bloodstream with it; lactate crosses the blood-brain barrier readily and stimulates BDNF production, which supports and amplifies neuroplastic processes. Cortisol, far from being the problem, is part of the adaptive signal driving the benefit.

Wood is direct: "There are several people out there saying 'don't do high intensity exercise, it releases cortisol, that's stressful' — this study directly shows that working really hard, releasing a lot of cortisol in high-intensity interval training, actually improves hippocampal structure and function." Within the study's own analyses, harder effort correlated with greater brain benefit.

The protocol isn't punishing in terms of weekly commitment. One day of genuine high-intensity intervals — 4×4 minutes at 85–95% max HR with three-minute rests — appears sufficient to deliver structural hippocampal protection that outlasts the training block by years. The discomfort during those sessions is the dose.

Cardio builds gray matter; resistance training builds white matter — and only one protects the structure most closely tied to cognitive decline

White matter changes are among the strongest predictors of age-related cognitive decline — and only resistance training appears to drive the molecular signal that maintains them.

Wood draws a clean mechanistic line. Aerobic exercise primarily targets gray matter structures including the hippocampus, largely through lactate-driven BDNF production. Resistance training primarily targets white matter — the myelin-sheathed axon tracts connecting cortical regions — through IGF-1, which is "particularly increased with resistance training" and "really critical to the development of white matter," both in utero and throughout the lifespan.

White matter constitutes roughly 60% of the human brain (higher than any other species) and is where information travels fast. When white matter lesions accumulate with age and poor cardiovascular health, processing speed and executive function fall first. "Changes in white matter structure with age are one of the best predictors of cognitive decline," Wood says.

The resistance protocol that appears consistently across the handful of RCTs Wood cites isn't complicated: two to three sessions per week, five to six exercises, three sets of 8–12 reps, multi-joint movements — leg press, chest press, lat pulldown, shoulder press. After six to twelve months, studies measure significant improvements in white matter structure and accompanying gains in executive function.

Neither mode substitutes for the other. Cardio-only training leaves the IGF-1 signal and white matter largely unaddressed. Resistance-only training misses the hippocampal stimulus that comes from aerobic intensity and lactate. "They seem to be having very different effects in terms of the structure and function of the brain long term," Wood says. The brain needs both, through entirely different pathways, to cover its full structural maintenance requirements.

Flow is the maximal expression of a learned skill — not a method for building one, and chasing it during practice is counterproductive

A third of training sessions are going to feel terrible. Wood's position: that's the system working correctly.

He introduces a concept from the sports psychology literature called the clutch state — less famous than flow but more practically important for anyone trying to build skill. Flow, as Wood defines it, is "the maximal expression of a complex learned skill": you're at the edge of your current abilities, and the execution is happening almost without conscious effort. The clutch state occupies the same optimal arousal level on the performance curve, but it still feels like hard cognitive and physical work. You slog through it. You perform well anyway.

The distinction matters because flow and clutch states have opposite relationships to learning. Flow requires operating inside your current capability ceiling. The moment you push past it — into genuine error, friction, repetitions of things you can't quite do yet — you exit flow. But that exit is exactly what drives neuroplasticity. "If you want to get better at that skill," Wood says, "you have to work even further beyond your current capacities, which will move you out of flow."

Some voices in performance culture have gone further and suggested that optimal learning happens in flow. Wood finds this mechanistically backwards. Learning is what happens in the error-prone, frustrating sessions. Flow is what shows up later as the accumulated expression of that hard work.

His realistic framing of any skill-building program: expect roughly a third of sessions to feel great, a third to feel average, and a third to be a grind you simply push through. All three are the process. "There's kind of this weird tension between what people are seeking versus what is actually just part of the grind of getting better." Stop manufacturing flow during skill-building. The clutch state is where plasticity lives.

Omega-3s and B vitamins for dementia prevention are biochemically co-dependent — supplementing either one alone likely delivers no cognitive protection

Three separate randomized controlled trials have established the same co-dependency. Give someone B vitamins when their omega-3 status is poor: no cognitive benefit. Give them omega-3s when their homocysteine is elevated: also no benefit. Each pathway fails without the other.

Wood walks through the sequence. The VITACOG trial from Oxford gave B vitamins to people with elevated homocysteine — homocysteine dropped, but cognitive outcomes didn't improve in those with low omega-3 levels. The B-PROOF trial replicated the finding. The OmegAD trial ran the experiment in reverse: omega-3 supplementation produced no cognitive benefit in participants with elevated homocysteine. "There are now at least three randomized control trials that have shown that omega-3 status and B vitamin status interact and they're dependent on one another."

The test to run first is homocysteine. Standard lab reference ranges are actively misleading here: the normal upper limit runs to 15–16 μmol/L, but Wood's target is 10–11. "We know that risk is definitely elevated above 13 and is probably elevated above sort of 10 to 11." Anyone sitting above that threshold who wants cognitive protection needs to address both B vitamins (especially B12, folate, and B6) and omega-3s simultaneously — not sequentially, not one at a time.

This is also why so many individual-nutrient trials keep coming up null. The field tests one variable at a time in a system that's co-dependent by design. "If we're not going into a study actually looking at what nutrients this person needs and then supplementing with them, you're not going to find any effect — you shouldn't be surprised when the study doesn't show anything." The failure mode isn't in the nutrients; it's in the study design.

Caffeine makes you feel sharper while measurably degrading the complex cognitive performance that actually matters

Caffeine feels like it sharpens thinking. On complex working memory tasks, it doesn't.

On the N-back task — where subjects track whether a stimulus appeared two or three positions ago in a sequence — people who take caffeine make more errors than those who don't, and respond too quickly without actually processing the information. They also rate their own performance as better than the caffeine-free group does. The dissociation between perceived and actual function isn't subtle; Wood notes it tracks across stimulant classes.

A paper in Science gave methylphenidate (Ritalin) to adults without ADHD and found the same pattern: felt sharper, performed worse on high-order cognitive tasks. The cannabis version runs in the opposite direction — users feel more creative while outside observers find no creativity gains — but the structural failure is identical. The substance breaks the internal feedback loop between how you feel and how you're actually doing.

What exercise-primed arousal does differently is preserve that loop. A 20–30 minute jog or a brief resistance session raises catecholamines and cortisol endogenously, moving you up the arousal curve without decoupling your sense of performance from your actual performance. "That endogenous increase in arousal using things like exercise is a much more reliable way to improve performance because you don't kind of get this dissociation," Wood says.

Caffeine isn't without value — it can sustain alertness and motivation for tasks that primarily demand persistence. But for sessions requiring genuine high-order reasoning, error detection, or active skill acquisition, exercise-primed arousal before the session is mechanistically superior to any stimulant taken in its place.

Processing speed training — not crosswords, not sudoku — is the only cognitive intervention with 20-year evidence for significantly reducing dementia risk

Twenty years after a single training intervention, one type showed up with a significantly reduced dementia risk. Not memory training. Not reasoning. Processing speed.

Wood walks through the ACTIVE trial — still the largest pure cognitive training study ever run in older adults, conducted in the US in the 1990s. Three groups: memory training (mnemonics, memory palaces), reasoning training (pattern recognition in numbers and letters), and visual processing speed training (stimuli flashing on screen for shrinking durations, sometimes hundreds of milliseconds, requiring subjects to register what appeared and where). A recent secondary analysis found that the processing speed group — particularly those who received booster sessions at one and three years — had a significantly decreased risk of dementia 20 years later. The mechanism, Wood says: "that kind of training improves cholinergic signaling in the forebrain which we know is susceptible to the processes of dementia."

Processing speed is distinct from reaction time. Reaction time — the basic startle response to a visual stimulus — declines slowly from the 30s onward. Processing speed, which requires the brain to actively interpret and remember what it just perceived, stays relatively stable until around age 60 and then drops steeply.

The contrast with crosswords is pointed. Referencing Gloria Mark's work, Wood notes that crosswords and sudoku "are less of a true cognitive challenge — it's almost more of a meditative effect. You're focused but not challenged." The activities that qualify for genuine processing-speed stimulus: competitive ball sports, martial arts, music performance under real time pressure, driving in complex environments, and formal software like Brain HQ, which was used in the POINTER trial. Being simultaneously focused and challenged is the requirement. Either one alone doesn't build the capacity that matters.

Cognitive decline drops in steps after major illness — which means infection avoidance belongs in any serious dementia prevention framework

Cognitive decline isn't a gradual slope. It's a staircase — and the drops correspond to hospitalizations.

Wood points to longitudinal data from the Adult Changes in Thought study (University of Washington) and the Rush Memory and Aging Project, both of which tracked the same individuals across repeated measurements over years. People who suffered significant illness between assessments showed a step-change drop in cognitive function. People who were hospitalized showed a larger drop still. Between illness events, the trajectory was comparatively flat.

The biological cascade is legible: serious illness means sharply reduced stimulation — you're homebound, sedentary, not engaging socially or cognitively — compounded by the neuroinflammatory effects of the infection itself and disrupted sleep and nutrition. Every one of those components independently degrades the inputs that maintain brain function. Combined, they register as a discrete loss that's difficult to climb back from.

This reframing gives Wood a structural reason to fold vaccination and immune health into cognitive health strategy — not as a separate domain but as part of the same architecture. He's careful about the shingles vaccine data: three natural experiments in Wales, Australia, and Canada found that people who newly became eligible for the shingles vaccine had lower subsequent dementia risk than those who missed eligibility by a single day. The signal held consistently across all three populations, though Wood acknowledges confounding concerns and notes a proper RCT is now being planned.

"If I can do as much as I can to minimize the chance that I get really sick," Wood says, "because what happens then is I'm at home, I'm not receiving any stimuli, any inputs, I'm not moving, I'm not eating well — then over time that could change the overall trajectory."

Every major illness avoided or shortened may preserve a cognitive step that would otherwise be lost.

The real edge in brain health isn't finding the right input — it's identifying which inputs interact

The frame that emerges from Wood's work — but wasn't fully spelled out in this conversation — is that the most important discoveries in cognitive health over the next decade will probably look like the omega-3 and B vitamin finding: not new protective factors, but previously invisible co-dependencies between factors we already know about. Exercise modalities interact. Nutrients interact. Physiological state interacts with the cognitive challenge in front of you. The field's default approach of testing one variable at a time keeps producing null results in exactly the domains where the evidence for interaction is already clear.

The brain rewards the combination. Always has.

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Topics: neuroplasticity, exercise and brain health, HIIT, cognitive decline, dementia prevention, resistance training, learning, flow state, omega-3, B vitamins, homocysteine, caffeine, stimulants, processing speed, concussion, shingles vaccine, cortisol, IGF-1, BDNF, hippocampus, white matter