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.
• Mechelli et al. found a larger parietal cortex in the brains of people who were bilingual compared to matched monolingual controls.
• 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
• Understanding the processes involved in plasticity has contributed to the field of neurorehabilitation. Following illness or injury to the brain, spontaneous recovery tends to slow down after a number of weeks so forms of physical therapy may be required to maintain improvements in functioning (e.g. movement therapy and electrical stimulation). This shows that, although the brain may have the capacity to 'fix itself' to a point, this process requires further intervention if it is to be completely successful.
• The brain's ability to rewire itself can sometimes have maladaptive behavioural consequences. 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.
• Functional plasticity tends to reduce with age. The brain has a greater propensity for reorganisation in childhood as it is constantly adapting to new experiences and learning.
• 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.