Plasticity and functional recovery of the brain after trauma

Brain plasticity

- The brain would appear to be 'plastic' in the sense that it has the ability to change throughout life. During infancy, the brain experiences a rapid growth in the number of synaptic connections it has. As we age, rarely-used connections are deleted and frequently-used connections are strengthened- a process known as synaptic pruning. This process allows lifelong plasticity where new neural connections are formed in response to new demands on the brain

Research into plasticity

- Maguire et al (2000) studies the brains of London taxi drivers and found significant more volume of grey matter in the posterior hippocampus than in a matched control group. This part of the brain is associated with the development of spatial and navigational skills. As part of their training, London taxi drivers must take a test called 'The Knowledge', which assess their recall of the city streets and possible routes. Maguire et al found that this learning experience alters the structure of the taxi drivers' brains. They also found that the longer the taxi drivers had been in the job, the more pronounced was the structural difference (positive correlation)

Functional recovery- After brain trauma

- A form of plasticity. Following damage through trauma, the brain's ability to redistribute or transfer functions usually performed by a damaged area (s) to other, undamaged area (s). Neuroscientists suggest this can occur quickly after trauma (spontaneous recovery) and then slow down after several weeks or months

Functional recovery- The brain during recovery

- The brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage. Secondary neural pathways that would not typically be used to carry out certain functions are activated or 'unmasked' to enable functioning to continue, often in the same way as before. This process is supported by a number of structural changes in the brain

• Axonal sprouting

• Denervation supersensitivity

• Recruitment of homologous areas on the opposite side of the brain.

Structural changes in the brain during recovery- Axonal sprouting

- The growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways

Structural changes in the brain during recovery- Denervation supersensitivity

- This occurs when axons that do a similar job become aroused to a higher level to compensate for the ones that are lost. However, it can have the unfortunate consequence of oversensitivity to messages such as pain

Structural changes in the brain during recovery- Recruitment of homologous (similar) areas on the opposite side of the brain

- This means that specific tasks can still be performed. An example would be if Broca's areas was damaged on the left side of the brain, the right-sided equivalent would carry out its functions. After a period of time, functionality may then shift back to the left side

Evaluation of plasticity: Weaknesses

- It may have negative behavioural consequences. Evidence has shown that the brain's adaption to prolonged drug use leads to poorer cognitive functioning in later life, as well as an increased risk of dementia (Medina et al 2007). Also, 60-80% of amputees have been known to develop phantom limb syndrome (the continued experience of sensations in the missing limb as if it were still there. These sensations are usually painful and are thought to be due to cortical reorganisation in the somatosensory cortex that occurs as a result of limb loss

- This suggests that the brain's ability to adapt to damage is not always beneficial

Evaluation of plasticity: Strengths

- It does not always decline sharply with age. Plasticity does reduce with age. however, Bezzola et al (2012) demonstrated how 40 hours of golf training produced changes in the neural representations of movement in participants ages 40-60. Using frMI, the researchers observed increased motor cortex activity in the novice golfers compared to a control group, suggesting more efficient neural representations

- This shoes that neural plasticity can continue throughout the lifespan

Evaluation of functional recovery: Strengths

- It has real-world application. Understanding the processes involved in plasticity has contributed to the field of neurorehabilitation. Understanding that axonal growth is possible encourages new therapies to be tried. For example constraint-induced movement therapy is used with stroke patients whereby they repeatedly practice using the affected part of their body while the unaffected part is restrained (such as arms)

- This shows that research into functional recovery is useful as it helps medical professionals know when interventions need to be made

Evaluation of functional recovery: Weaknesses

- The level of education may influence recovery rates. Schneider et al (2014) revealed that the more time people with a brain injury had spent in education, the greater their chances of a disability-free recovery. 40% of those who achieved this recovery had more than 16 years' education compared to about 10% of those who had less than 12 years' education

- This would imply that people with brain damage who have insufficient DFR are less likely to achieve a full recovery