Plasticity and functional recovery of the brain after trauma

• Plasticity = describes the brain's tendency to change and adapt as a result of experience and new learning
• Functional recovery = a form of plasticity. Following damage through trauma, the brain's ability to redistribute or transfer functions usually performed by a damaged area to other undamaged areas.
• As we age, rarely used connections are deleted and frequently used connections are strengthened (synaptic pruning).
• 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, peaking at approximately 15,000 at age 2-3 years. This is about twice as many as there are in the adult brain.
• Recent research suggests that at any time in life existing neural connections can change, or new neural connections can be formed, as a result of learning and experience (plasticity).
• It was originally thought that such changes were restricted to the developing brain within childhood, and that the adult brain, having moved beyond a critical period, would remain fixed and static in terms of function and structure.
• Maguire et al. studied the brains of London taxi drivers and found significantly more volume of grey matter in the posterior hippocampus than in a matched control group. This part of the brain is associated with development of spatial and navigational skills. London cabbies must take a complex test which assesses their ability to recall the city streets and possible routes. It appears that the result of this learning experience is to alter the structure of the taxi drivers' brains. The longer they had been in the job, the more pronounced the structural difference.
• Draganski et al. imaged the brains of medical students three months before and after their final exams. Learning-induced changes were seen to have occurred in the posterior hippocampus and the parietal cortex presumably as a result of the exam.
• Following physical injury, unaffected areas of the brain are often able to adapt and compensate for those areas that are damaged. The functional recovery that may occur in the brain after trauma is another example of neural plasticity. Neuroscientists suggest that this process can occur quickly after trauma and then slow down after several weeks or months.
• 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 to enable functioning to continue, often in the same way as before.
• Axonal sprouting = the growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways
• One strength of functional recovery research is its real-world application. Understanding the processes involved in plasticity has contributed to the field of neurorehabilitation. Simply 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. This shows that research into functional recovery is useful as it helps medical professionals know when interventions need to be made.
• One limitation of plasticity is that it may have negative behavioural consequences. The brain's adaption to prolonged drug use has been shown to result in poorer cognitive functioning as well as an increased risk of dementia later in life. Also, 60-80% of amputees have been known to develop phantom limb syndrome (the continued experience of sensations in the missing limb). Theses sensations are usually unpleasant, painful and 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.
• A strength is that brain plasticity may be a life-long ability. In general plasticity reduces with age. However, Bezzola et al. demonstrated how 40 hours of golf training produced changes in the neural representation of movement in participants aged 40-60. Using fMRI, the researchers observed reduced motor cortex activity in the novice golfers compared to a control group, suggesting more efficient neural representations after training. This shows that neural plasticity does continue throughout the lifespan.
• One limitation of functional recovery is that the level of education may influence recovery rates. Schneider et al. revealed that the more time people with a brain injury had spent in education (taken as an indication of 'cognitive reserve') the greater their chances of a disability-free recovery (DFR). 40% of those who achieved DFR 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.