Brain Plasticity and Functional Recovery

The brain was once thought to be a fixed, unchanging organ — "hardwired" from early childhood. Modern neuroscience has overturned this view. The brain is remarkably plastic — it can change its structure and function in response to experience, learning, and injury throughout the lifespan. This property, known as neuroplasticity, has profound implications for understanding learning, memory, rehabilitation, and recovery after brain damage.

Key Definition: Neuroplasticity (brain plasticity) is the brain's ability to change and adapt its structure and function in response to experience, learning, or injury. This includes the formation of new synaptic connections, the strengthening or weakening of existing connections, and, in some cases, the growth of new neurons.

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Mechanisms of Neuroplasticity

Synaptic Plasticity

The most common form of neuroplasticity involves changes at the synaptic level:

• Long-term potentiation (LTP) — when a synapse is repeatedly stimulated, the connection between the presynaptic and postsynaptic neurons becomes stronger. This is believed to be the neural basis of learning and memory (Bliss & Lømo, 1973).
• Long-term depression (LTD) — when a synapse is consistently understimulated, the connection weakens. This is thought to be important for forgetting and for making the neural network more efficient.
• Synaptic pruning — during development (especially adolescence), unused or weak synaptic connections are eliminated. This "pruning" refines neural circuits, making them more efficient. The principle is often summarised as "use it or lose it."

Key Definition: Synaptic pruning is the process by which excess neurons and synaptic connections are eliminated during development, strengthening frequently used pathways and removing those that are rarely used.

Dendritic Growth and Branching

When neurons are frequently stimulated, their dendrites can grow additional branches, increasing the number of synaptic connections. This is a structural change that can be observed under a microscope and is one mechanism by which experience physically reshapes the brain.

Neurogenesis

Neurogenesis — the birth of new neurons — was long thought to be impossible in the adult brain. However, research has shown that new neurons can be generated in certain regions, particularly the hippocampus (involved in memory) and the olfactory bulb (involved in smell). Eriksson et al. (1998) demonstrated neurogenesis in the adult human hippocampus using post-mortem tissue from cancer patients who had received a marker chemical (BrdU) that labels dividing cells.

Key Definition: Neurogenesis is the process by which new neurons are formed in the brain. In adults, this occurs primarily in the hippocampus and is believed to play a role in learning and memory.

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Evidence for Neuroplasticity

Maguire et al. (2000) — London Taxi Drivers

Study: Eleanor Maguire and colleagues used structural MRI to compare the brains of 16 London taxi drivers with those of 50 control participants. London taxi drivers must pass "The Knowledge" — an extremely demanding spatial navigation test requiring memorisation of 25,000 streets and thousands of landmarks.

Findings:

• Taxi drivers had a significantly larger posterior hippocampus (the region associated with spatial memory and navigation) compared to controls.
• The volume of the posterior hippocampus was positively correlated with the number of years spent as a taxi driver — the longer the experience, the larger the posterior hippocampus.
• However, the anterior hippocampus was smaller in taxi drivers than in controls, suggesting a possible trade-off.

Evaluation (AO3):

• Strength — provides strong evidence that experience can physically change brain structure, supporting neuroplasticity.
• Strength — the correlation with years of experience strengthens the causal interpretation (it is not simply that people with larger hippocampi choose to become taxi drivers).
• Limitation — correlational design — it is still possible that individuals who become taxi drivers already have a natural predisposition for larger hippocampi (self-selection bias).
• Limitation — small sample of male taxi drivers — limits generalisability to other populations and tasks.

Draganski et al. (2004) — Jugglers

Study: Bogdan Draganski and colleagues taught 24 non-jugglers to juggle three balls over a three-month period, using structural MRI to scan their brains before training, after three months of practice, and three months after they stopped juggling.

Findings:

• After three months of juggling practice, there was a significant increase in grey matter in the mid-temporal area (V5/MT — associated with visual motion processing) and the left posterior intraparietal sulcus.
• Three months after participants stopped juggling, the grey matter increase had partially reversed, although it had not returned entirely to baseline levels.

Evaluation (AO3):

• Strength — experimental design with repeated measures — participants served as their own controls, eliminating individual differences.
• Strength — demonstrates that plasticity is reversible — the brain adapts when stimulated and de-adapts when stimulation ceases. This supports the "use it or lose it" principle.
• Limitation — the study measured volume changes in grey matter but did not determine the cellular mechanism (e.g., dendritic growth, neurogenesis, or glial cell changes).
• Limitation — relatively small sample — only 24 participants.

Exam Tip: Maguire et al. (2000) and Draganski et al. (2004) are the two key studies for plasticity. Learn them in detail — including method, findings, and at least two evaluation points each. Examiners expect you to go beyond simply describing the findings.

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Functional Recovery After Brain Trauma

When the brain is damaged — by stroke, traumatic brain injury, or surgery — it can sometimes recover lost functions. This process is called functional recovery and relies heavily on neuroplasticity.

Mechanisms of Functional Recovery

Mechanism	Description
Neural reorganisation	Undamaged areas of the brain take over functions previously performed by the damaged area. Adjacent cortical regions may expand into the damaged territory.
Axonal sprouting	Undamaged neurons grow new axonal branches (sprouts) that form new synaptic connections with neurons in the damaged area, partially restoring function.
Denervation supersensitivity	Surviving neurons become more sensitive to neurotransmitters to compensate for the loss of input from damaged neurons.
Recruitment of homologous areas	The corresponding area in the opposite hemisphere may take over some functions (e.g., right-hemisphere language areas compensating after left-hemisphere stroke).
Stem cells	Research is exploring whether neural stem cells can be used to generate new neurons to replace damaged ones. This remains largely experimental.
Neurogenesis	New neurons generated in the hippocampus and possibly other regions may contribute to recovery, though the extent of this in humans is debated.

Evidence for Functional Recovery