Neuroplasticity: The Changeable Brain

Your brain rewires itself with every experience. Synaptic plasticity, structural change, London taxi drivers, phantom limbs and recovery after stroke — the evidence that the adult brain keeps changing.

Neuroplasticity is the nervous system's capacity to change its structure and function in response to experience, learning or injury. It was once thought mainly to belong to childhood. We now know the adult brain changes throughout life.

Kinds of plasticity

Synaptic plasticity: connections strengthen (long-term potentiation) or weaken (long-term depression) depending on activity. The Canadian psychologist Donald Hebb proposed in 1949 that when one neuron repeatedly helps fire another, the connection between them strengthens — summarised later by Carla Shatz as "cells that fire together wire together". Structural plasticity: dendritic spines appear and disappear within hours to days; axons sprout. Myelin plasticity and, in some regions, possibly new neurons add further routes for change. Cortical remapping: whole areas can be taken over by new functions.

Evidence from everyday expertise

In a well-known 2000 study, Eleanor Maguire and colleagues found that London taxi drivers, who memorise thousands of streets ("the Knowledge"), had on average a larger posterior hippocampus than control participants, with size related to years of experience; a later study following trainees supported a causal effect. Musicians show enlarged representations of the fingers they use most. Blind people who read Braille use parts of the visual cortex for touch.

Phantom limbs

After amputation, many people feel the missing limb, sometimes painfully. The neuroscientist V. S. Ramachandran found that touching some patients' faces produced sensations in the phantom hand — the face area of the sensory cortex had invaded the neighbouring, now-silent hand area. His mirror box, which tricks the brain into "seeing" the missing limb move, helps some patients with phantom pain.

Recovery and limits

After a stroke, surviving regions can take over some lost functions, especially with intensive, repetitive rehabilitation. But plasticity has limits: it declines with age, isn't always helpful (chronic pain and addiction involve plasticity too), and the popular claim that you can "rewire your brain" for anything in a few weeks is oversold.