The concept of brain plasticity

Brain plasticity refers to the capacity of the brain to modify its structure and function based on environmental influences. This adaptability allows individuals to learn new skills and adjust to changes throughout life.

How brain plasticity operates

Information moves through the brain via pathways connecting neurons across synapses. Encountering new information prompts the formation of fresh neural pathways. Repeated use of a pathway reinforces the connections between neurons, making it stronger. In contrast, unused pathways weaken over time. This ongoing process of rewiring and restructuring underpins learning and environmental adaptation.

For example, when learning a new skill, initial attempts are often clumsy. With repeated practice, the relevant neural pathways strengthen, leading to improved performance.

Plasticity across the lifespan

Plasticity was once believed to be limited to infants and children, where it is most pronounced due to rapid brain development. However, research now confirms that plasticity persists into adulthood, enabling ongoing adaptation and learning.

Cortical representation and reorganisation

Specific regions in the somatosensory cortex and motor cortex correspond to different body parts, a phenomenon known as cortical representation. Cortical reorganisation involves alterations in these representations, reflecting the brain's plastic nature.

Research evidence for plasticity

Several studies demonstrate brain plasticity through changes in cortical areas linked to repeated activities or training.

Elbert et al. (1995) - Plasticity in musicians

• Method - Ten string instrument players (violin, cello, or guitar) were compared with five non-musicians. Magnetic source imaging measured the somatosensory cortex area linked to the left hand digits.
• Results - The cortical area for left hand digits was larger in musicians than in controls.
• Conclusions - Extensive sensory demands on the left hand from playing instruments lead to brain structural changes, supporting plasticity.
• Evaluation - Critics suggest the larger representation might stem from genetics rather than practice. The small sample limits generalisability.

Karni et al. (1995) - Motor skill learning

• Method - Functional magnetic resonance imaging (fMRI) tracked brain activity during and after three weeks of practising a finger movement sequence.
• Results - Practising expanded the activated motor cortex area when performing the sequence.
• Conclusions - Learning and repetition cause cortical reorganisation, evidencing plasticity.

Nudo et al. (1996) - Reversible changes in monkeys

• Method - Adult monkeys' motor cortex was mapped before and after training on digit-focused tasks, then forearm-focused tasks.
• Results - Digit training enlarged digit representation; forearm training expanded forearm representation while shrinking digit areas.
• Conclusions - Plastic changes are ongoing and reversible, at least in primates.

Functional recovery from brain damage

Brain damage from causes like head injuries, strokes, tumours, or infections can impair functions, such as speech loss from Broca's area damage or hearing loss from auditory cortex harm. However, the brain can regain some functions through plasticity.

Mechanisms of functional recovery

Plasticity enables rewiring, where undamaged brain regions near the affected area assume the lost functions. This reorganisation helps restore abilities over time.

Constraint-induced movement therapy

Constraint-induced movement therapy (CIMT) is a rehabilitation approach for stroke patients with unilateral function loss. It restricts the unaffected side, compelling relearning with the affected side.

Advantages of CIMT

• Evidence of effectiveness - Multiple studies indicate CIMT induces cortical reorganisation, leading to function recovery or improvement.
• Broader applications - CIMT principles extend to conditions like aphasia from stroke, aiding speech recovery.

Disadvantages of CIMT

• Patient frustration - The therapy can be emotionally challenging due to forced reliance on the impaired side.
• Intensity requirements - Effectiveness demands rigorous schedules, such as hours of daily training on the affected limb and restraining the unaffected one for most waking hours over weeks.
• Limitations in severe cases - CIMT works best for mild to moderate damage; extensive brain injury makes recovery harder.