Brain plasticity changes throughout a lifetime, not just something that happens all the time.
In the 1970s, psychologist Hans-Lukas Teuber studied brain damage in World War II soldiers.
Key finding: Younger soldiers recovered better from brain injuries than older ones.
This suggests that brain flexibility diminishes with age.
The Brain as a Changing Landscape
Young brains are like the Earth thousands of years ago: flexible, with borders that can shift.
As brains age, they settle into patterns, much like how country borders and constitutions stabilize over time.
Example: The American Constitution had 12 amendments in its first 13 years, but now changes occur much less frequently.
Silicon Valley startups are highly flexible, but as companies grow, they become rigid and bureaucratic—similar to brain development.
From Fluid to Crystallized Intelligence
Babies: Few built-in skills but immense flexibility.
Adults: Developed expertise at the expense of flexibility.
Trade-off: Young brains have fluid intelligence, whereas older brains develop crystallized intelligence.
Adults get better at certain skills but lose the ability to learn completely new ways of thinking easily.
Why Does Plasticity Decline?
1. Pruning of Neural Connections
Babies’ brains are massively interconnected.
At age 2, neurons have about 15,000 connections each.
Over time, unnecessary connections are pruned, keeping only the most useful pathways.
Example: EEG studies show that a baby’s brain responds to a sound with activity in both auditory and visual areas; adults’ brains localize this response to the auditory cortex only.
This pruning leads to efficiency but reduces flexibility.
2. Targeted Neuromodulation
Babies experience broad, widespread plasticity.
Adults undergo pointillist plasticity, meaning only small, specific areas of the brain change when necessary.
The neuromodulatory system (e.g., acetylcholine) narrows its impact over time, limiting broad-scale change.
Example: A child learning language absorbs all sounds, while an adult struggles with new phonemes.
The Concept of Sensitive Periods
Critical periods: Windows where certain abilities must be developed, or they become impossible later.
Examples:
Language acquisition: If children do not hear language before a certain age, they may never fully acquire it (e.g., Genie, the feral child).
Accent adaptation: Mila Kunis moved to the U.S. at 7 and lost her accent; Arnold Schwarzenegger moved at 21 and retained his.
Vision development: Children with misaligned eyes must receive treatment by age 6, or their visual cortex will never develop correctly.
The Role of Experience in Shaping the Brain
Plasticity follows the stability of incoming data:
Stable inputs (e.g., visual edges, phonemes, grammar) → The brain locks them in early.
Unstable inputs (e.g., social interactions, motor skills, object recognition) → The brain keeps them flexible for a longer time.
Different parts of the brain solidify at different rates:
Primary visual and auditory cortices: Lock down early.
Higher-order cognitive areas (e.g., object recognition, language comprehension): Remain flexible longer.
Motor learning: Stays plastic throughout life (e.g., learning to surf, ride a bike, or use new tools).
Adult Brain Plasticity
While plasticity declines, it never disappears completely.
Examples of adult brain plasticity:
Learning to juggle increases brain volume in relevant areas.
Black cab drivers in London develop larger hippocampi due to memorizing city streets.
The Religious Order Study showed that nuns with Alzheimer’s remained cognitively sharp due to lifelong mental and social engagement.
Maintaining Plasticity as We Age
Key principle: Engage in activities that challenge the brain.
Practical strategies:
Switch daily routines (e.g., wear your watch on the opposite wrist, brush your teeth with your non-dominant hand).
Rearrange furniture, paintings, or workspaces regularly.
Take different routes when commuting to introduce novelty.
Stay socially active—interacting with people is cognitively demanding.
Encourage elderly individuals to stay engaged in mentally challenging activities to maintain cognitive function.
Summary
Plasticity decreases with age, but not uniformly across the brain.
The brain prioritizes efficiency over flexibility, stabilizing useful pathways.
Some areas (e.g., primary sensory cortices) solidify early, while others (e.g., higher cognition) remain flexible.
New learning is always possible, but it requires effort and motivation.
Staying engaged in learning and social activities is crucial for lifelong cognitive health.
