Neuroplasticity: How the Brain Reorganizes Itself, Adult Neurogenesis, and the “Use It or Lose It” Principle
Before the mid-20th century, mainstream neuroscience held that adult brain neural connections were fixed — neurons once dead are irreplaceable, adult brains undergo no further structural changes. This dogma was systematically overturned over the past 30 years: **Neuroplasticity** — the brain’s capacity to change structure and function through experience — is now understood to persist across the lifespan, though diminishing significantly with age.
## Classic Evidence: London Taxi Drivers’ Hippocampi
Eleanor Maguire’s (UCL) milestone 2000 study: compared to controls, experienced London taxi drivers had significantly larger **posterior hippocampus** gray matter volume, correlated with years of driving experience. London cabbies must memorize the complex road network (“The Knowledge,” ~3–4 years training), making extreme demands on the hippocampus (critical for spatial memory), leading to experience-dependent expansion. This proved **intensive skill training can cause measurable brain structural changes**.
## Adult Neurogenesis: New Neurons in the Hippocampus
**Adult Neurogenesis**: in some brain regions (mainly hippocampal dentate gyrus), new neurons can still be produced in adulthood — overturning the “adult neurons are irreplaceable” dogma. Aerobic exercise (raises BDNF levels), environmental enrichment (novel stimulation), and some antidepressants (SSRIs) promote hippocampal neurogenesis; chronic stress and sleep deprivation suppress it — providing a partial mechanistic explanation for exercise’s and sleep’s protective effects on cognitive function.
**Use-Dependent Plasticity**: congenitally blind people’s visual cortex (normally processing visual information) gets “requisitioned” for touch and language processing — showing that when one sensory input is absent, its corresponding cortex doesn’t simply “idle” but is “colonized” by adjacent functional systems.
