neuroplasticity

🧠 Neuroplasticity – Core Concepts

Definition

• Neuroplasticity = the brain’s ability to change its structure, function, or organisation in response to experience and behaviour (physical or cognitive).

• Behaviour both reflects and drives plasticity.

• It is where:
  

  • Biology → what physically changes in the brain

  • Psychology → what changes in behaviour/thoughts/emotions

  • meet.

Plasticity Can Involve:

• Strengthening synapses

• Weakening synapses

• Reorganising circuits

• Changing which brain areas are used

• ⚠ Not unlimited flexibility.

📜 Historical Perspective

Old View — “Fixed Brain”

• Adult brain cannot change or regenerate.

• Neurons formed early in life.

• Damage = permanent deficits.

• Idea persisted because:
  

  • Neurons are post-mitotic (don’t divide).

Key Figures

William James

• Suggested brain function is not fixed across life.

• Early neuroplasticity concept.

Donald Hebb (1949)

• Linked psychology + neurobiology.

• Proposed cell assemblies.

• Hebb’s Rule: “Neurons that fire together wire together.”

• Foundation for neural network theory & AI.

🔄 From Experience to Behaviour Change

Experience (learning, stress, therapy)

→ Neural plasticity (synapses & circuits change)

→ Behavioural change (skills, habits, emotions)

Psychology Terms — Biological Meaning

• Learning → persistent synaptic change

• Memory → stabilised neural networks

• Habit → efficient low-effort circuits

• Extinction → inhibition (not erasure) of pathway

• Relapse → reactivation of strengthened circuits

🧪 Brain Imaging Advances

PET (Positron Emission Tomography)

• Uses radioactive glucose tracer

• Highlights energy use → activity

fMRI (Functional MRI)

• Uses BOLD signal

• Measures oxygen use in active brain areas

🧬 Brain Cell Types

• Oligodendrocytes → myelinate CNS axons

• Astrocytes → regulate synapse environment, maintain BBB

• Microglia → immune defence, remove debris

• Endothelial cells → control blood-brain barrier entry

• Ependymal cells → line ventricles/spinal cord, make CSF

🔧 Types of Neuroplasticity

1⃣ Structural Plasticity

Physical neuron/synapse changes:

• Dendrite growth/retraction

• Synapse formation/elimination

• Spine number changes

• Limited adult neurogenesis

• Driven by activity + gene expression

2⃣ Functional Plasticity

Function reassigned to new brain areas:

• Language shifting after stroke

• Visual cortex used for touch in blindness

• Brain reorganises — does not regrow lost regions

⚠ Structural and functional plasticity often occur together.

⚡ Synaptic Plasticity (Key Mechanism)

Definition

Activity-dependent change in synaptic strength.

Importance

• Core mechanism of learning & memory

Two Directions

• LTP = strengthening

• LTD = weakening

➕ Long-Term Potentiation (LTP)

Concept

• Repeated activation → stronger synapse

Effects

• More efficient neuron communication

• Higher chance of future activation

Behavioural Role

• Learning associations

• Memory consolidation

Molecular Mechanism (Glutamate Synapses)

• NMDA receptors detect coincidence

• Ca²⁺ enters postsynaptic neuron

• Signalling cascade triggered

• More AMPA receptors inserted

• Stronger response to glutamate

➖ Long-Term Depression (LTD)

Concept

• Persistent synaptic weakening

Functions

• Prevents over-excitation

• Refines circuits

• Supports unlearning

Behavioural Role

• Flexibility

• Updating learning

Molecular Mechanism

• Glutamate release

• NMDA (or mGluR) activation

• Moderate sustained Ca²⁺ influx

• Phosphatases activated

• AMPA receptors removed

🌱 Neurogenesis

Definition

• Creation of new neurons

Key Facts

• Mostly occurs before birth

• Adult neurogenesis limited (e.g., hippocampus)

Promoted By

• Exercise

• Learning

• Good sleep

• Some antidepressants

Inhibited By

• Stress

• Aging

• Inflammation

• Some drugs

Relevance

• Depression

• Memory

• Potential therapy in stroke & dementia

(Fred Gage — key researcher)

🌿 Synaptic Sprouting & Pruning

Sprouting (Adding Connections)

• New axon branches/dendritic spines

• Occurs in development, learning, injury

• Promoted by:
  

  • Activity

  • Use

  • Neurotrophic factors

  • LTP

• Supports:
  

  • Recovery

  • Learning capacity

  • Exploration

Pruning (Removing Connections)

• Eliminates weak/unused synapses

• Occurs in development, learning, injury

• Promoted by:
  

  • Inactivity

  • Weak correlation

  • LTD

• Involves:
  

  • Spine retraction

  • Microglia activity

• Supports:
  

  • Efficiency

  • Skill refinement