The transfer problem
Practise a working-memory task for a month and you will get impressively better at that task. The question researchers care about is whether the gain transfers: does it show up on a different task that taps the same underlying ability, and does it show up in daily life?
Near transfer — to closely similar tasks — is commonly found. Far transfer to general reasoning is where the evidence collapses. Large preregistered trials and meta-analyses that control for placebo effects and expectancy repeatedly find effects close to zero.
This is not a reason for fatalism. It is a reason to be precise: the things that reliably change cognitive performance are mostly not marketed as brain training.
Sleep is the largest reversible factor
Restricting sleep to five or six hours for a week produces measurable declines in attention, working memory, and problem-solving, and — importantly — people badly underestimate their own impairment while it is happening.
Recovery is fast. Consistent sleep timing, a dark cool room, and no alcohol in the hours before bed will do more for next week's thinking than any app. If you are testing yourself, a poor night can plausibly cost you several points on any timed measure.
Aerobic exercise and vascular health
Regular aerobic activity is associated with better executive function and slower age-related decline, with plausible mechanisms: improved cerebral blood flow, increased BDNF, and better metabolic health. Effect sizes in randomised trials are modest but consistent, and they are largest in older and previously sedentary adults.
The dose that shows up in the literature is unglamorous: about 150 minutes a week of moderate activity, sustained for months. Resistance training adds benefits for older adults, particularly for executive control.
Learning hard things beats playing easy games
Crystallised ability — knowledge, vocabulary, domain expertise — grows throughout adult life, and it does most of the work in real problems. Learning a language, an instrument, statistics, or a craft builds structured knowledge you can actually deploy.
The mechanism is not mystical. Expertise reorganises how you chunk information, which effectively expands working memory within that domain. A chess master remembers a board position at a glance not because of superior raw memory but because they see five meaningful patterns where a novice sees thirty pieces.
Choose difficulty deliberately. Practice that feels effortless is rehearsal; practice that feels slightly beyond you, with feedback, is where learning happens.
Hearing, vision and the boring interventions
Uncorrected hearing loss is one of the strongest modifiable risk factors for cognitive decline identified in large longitudinal reviews. When listening consumes cognitive resources, less is left for comprehension and memory, and social withdrawal compounds the effect.
Correcting vision, treating sleep apnoea, managing blood pressure and diabetes, and reviewing medications with sedative effects all belong on the list. None of them sell subscriptions, which is roughly why you hear less about them.
What about supplements and nootropics?
For people with an actual deficiency, correcting it helps: B12, iron, vitamin D, iodine. For everyone else, the evidence for supplements improving reasoning in healthy adults is weak, inconsistent, or confined to small unblinded studies.
Caffeine is a genuine exception with a narrow remit: it improves alertness and sustained attention, especially when you are underslept, and does little for reasoning itself. Tolerance builds quickly and rebound fatigue is real.
Practice effects: why your second test score rises
Retaking the same or a similar test typically produces a gain of several points, larger on non-verbal tasks and largest between the first and second attempt. You have learned the format, the rule families, and the pacing.
This is worth knowing before you conclude that some routine made you smarter. If you want a meaningful comparison, use a different item set, leave months between attempts, and hold conditions constant: same time of day, same rested state, no interruptions.