Psychology › Brain & biology › Neurons and synapses
Neuroplasticity: the brain rewires with use
Hebb's rule 1949· Concept
Well replicatedStrong, repeated evidence.
The brain physically changes with experience: connections strengthen, weaken, sprout or get pruned throughout life.
See it on the Psychology map →What it says
In 1949 Canadian psychologist Donald Hebb proposed that when one neuron repeatedly helps fire another, the link between them strengthens, later summed up as 'cells that fire together wire together'. In 1973 Tim Bliss and Terje Lømo found exactly that, long-term potentiation, in rabbit brains. Practice reshapes the brain: in a 2004 German study, three months of learning to juggle enlarged visual-motion areas, which partly shrank back after practice stopped. After a stroke, nearby areas can take over lost functions.
Why it matters
It overturned the belief that the adult brain is fixed. It is the basis of all learning and of stroke rehabilitation, and also explains how habits and addictions become ingrained.
The evidence
Status: well replicated. Recordings from animal neurons, microscopes that film synapses forming, brain scans before and after training, and recovery studies after stroke. Plasticity is greatest in childhood but persists into old age.
Open questions
Whether childhood 'critical periods', such as for learning an accent-free language, can be reopened in adults; drugs including psychedelics are being tested, with early, uncertain results.
Inside this (1)
Connections (5)
▸Neuroplasticity: the brain rewires with use rewires connections between Neurons and synapsesWell replicated
The connection
Plasticity happens mainly at synapses. When neurons fire together repeatedly, the receiving side adds receptors and the link strengthens (long-term potentiation); unused links weaken and get pruned. Neurons also grow new branches and spines. Learning a skill or a street map is literally a change in the wiring between neurons.
Who showed it and when
Donald Hebb's 1949 book at McGill University in Montreal proposed the rule; Tim Bliss and Terje Lømo confirmed it in Oslo in 1973; Eric Kandel traced it in sea slugs.
The evidence
Microscopes now film individual synapses forming and vanishing in living mice; Kandel shared a 2000 Nobel Prize for showing that memory storage changes synapses.
Open questions
How memories stay stable while synapses constantly turn over; researchers debate whether a memory lives in specific synapses or in broader patterns of activity.
▸Brain-training games overpromised on Neuroplasticity: the brain rewires with useWell replicated
The connection
Brain-training companies sold neuroplasticity as a promise: since the brain rewires with practice, game drills would strengthen memory and attention for everyday life. The first half is true; practice does change the brain. But the change is mostly specific to the task practiced, so the leap to general sharpness was marketing, not evidence.
Who showed it and when
Lumosity, Posit Science and rivals, mid-2000s to 2010s; the 2014 scientists' consensus statement and the 2016 FTC case against Lumos Labs pushed back.
The evidence
Ads cited plasticity research directly; the FTC complaint documented unsupported claims; independent reviews show gains rarely transfer beyond trained tasks.
Open questions
Whether any kind of mental training transfers broadly, perhaps in older adults or combined with exercise, remains open, with researchers split.
▸Neuroplasticity: the brain rewires with use underlies Spacing and retrieval practiceWell replicated
The connection
Learning physically changes the brain: connections between neurons that fire together strengthen, as Donald Hebb proposed in 1949. Spacing and retrieval practice appear to work by repeatedly reactivating these connections, which builds more durable changes than one long session. The brain-level explanation is partly inferred from animal studies.
Who showed it and when
Hebb at McGill, 1949; long-term strengthening of synapses found by Timothy Bliss and Terje Lømo in Oslo, 1973; Eric Kandel's sea-slug studies, Nobel 2000.
The evidence
Animal studies show spaced training produces longer-lasting synaptic changes than massed training; human evidence is mostly indirect, from brain imaging.
Open questions
Exactly which cellular changes make spaced learning last longer in humans, and how synapse-level findings scale up to real study habits.
▸Neuroplasticity: the brain rewires with use persists into Aging: what declines and what doesn'tWell replicated
The connection
The brain keeps rewiring through old age, though more slowly. Older adults can learn new skills, such as juggling, a language or a new route, and scans show matching changes in gray matter. Plasticity is why exercise, hearing aids and new learning can help aging brains, and why recovery after a stroke is possible at any age.
Who showed it and when
Arne May's group in Germany showed in 2008 that 60-year-olds learning to juggle grew gray matter; Fred Gage's team reported new neurons in adult human brains in 1998.
The evidence
Brain-scan training studies, plus a 2011 trial in which a year of walking enlarged older adults' hippocampus by about 2%, offsetting one to two years of age-related shrinkage.
Open questions
Whether adult humans make meaningful numbers of new neurons; studies published in 2018 disagree sharply, possibly because of how brain tissue was handled.
▸Modifiable dementia risk factors partly act via cognitive reserve, built by Neuroplasticity: the brain rewires with useMixed evidence
The connection
Several modifiable factors, such as education, staying mentally and socially active, and treating hearing loss, are thought to work partly by building 'cognitive reserve': extra connections and backup strategies made possible by plasticity. A brain with more reserve can absorb more disease before symptoms show, which may delay dementia rather than stop the underlying damage.
Who showed it and when
Robert Katzman's 1988 autopsy study found some people with Alzheimer's plaques had shown no symptoms; Yaakov Stern at Columbia University developed the cognitive reserve idea from the 1990s.
How solid is it?
Autopsy and cohort studies repeatedly find education and mental activity delay symptoms despite similar brain damage; but reserve is inferred from that gap, not measured directly.
Open questions
Whether reserve is a real biological buffer or a label for 'symptoms came later than expected'; once symptoms start, people with high reserve may decline faster.