Plasticity and functional recovery of the brain after trauma

• Plasticity is when the brain changes and adapts (functionally and physically), as a result of experience and new learning.
• 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.
• As we age, rarely used connections gets deleted and frequently used connections are strengthened -  a process known as synaptic pruning. 
• Most 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. 

• Eleanor 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 the development of spatial and navigational skills in humans. 
• As past of the London taxi driver's training, they have to take a complex test called 'The Knowledge', which assesses their recall of the city streets and possible routers. 
• The result of this learning experience is to alter the structure of the taxi drivers' brains. 
• It's recorded that the longer they had been in the job, the more pronounced was the structural difference. 
• Draganski et al, also did a research who 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 as a result of the exam. 
• Mechelli at al, found a larger parietal cortex in the brains of people who were bilingual compared to matched monolingual controls. 

• After a physical injury or other forms of trauma such as the experience of a stoke
• 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
• Healthy brain areas may take over the functons of those areas that are damaged
• Neuroscientists suggest that this process can occur quickly after trauma and then slows down after several weeks or months
• At this point the individual may require rehabilitative therapy to further their recovery

• The brain rewires and reorganises 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 
• This process is supported by a number of structural changes in the brain including:
  • Axonal sprouting: The growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways
  • Reformation of blood vessels
  • Recruitment of homologous areas - on the opposite side of the brain to perform specific tasks. For example, if Broca's area was damaged on the left side of the brain, the right side would then carry out its functions. After a period of time, functionality may then shift back to the left side

Practical application

• The processes involved in plasticity has contributed to the field of neurorehabilitation
• Post-injury/illness to the brain, recovery tends to slow down after a number of weeks so forms of physical therapy may be required to maintain improvements in functioning
• Techniques may include movement therapy and electrical stimulation of the brain
• 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

Negative plasticity

• The brain's ability to rewire itself can sometimes have maladaptive behavioural consequences
• Prolonged drug use, has shown to result in poorer cognitive functioning and increased risks of dementia later in life
• 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 often unpleasant, painful and are thought to be due to cortical reorganisation in the somatosensory cortex, that occurs as a result of limb loss. 

Age and plasticity

• Plasticity tends to reduce with age
• During childhood the brain has greater propensity for reorganisation as when we are a child we are constantly learning new things and experiencing new things. Therefore the brain is always adapting.
• Ladina Bezzola et al, shows how 40 hours of golf training produced changes in the neural representation of movement in participants ages 40-60.
• Using fMRI, the researchers saw that there was a reduced motor cortex activity in the novice golfers compared to a control group
• This shows that neural plasticity does continue throughout the lifespan

Support from animal studies

• David Hubel and Torten Wiesel did a study on plasticity in animals
• This study involved sewing one eye of kitten shut and analysing the brain's cortical responses
• They found that the area of the visual cortex associated with the shut eye was not idle but continued to process information from the open eye

The concept of cognitive reserve

• Evidence suggests that a person's educational attainment may influence how well the brain functionally adapts after injury
• Eric Schneider et al, found that the more time brain injury patients has spent in education, the greater their chances of a disability-free recovery
• 2/5th's of patients who achieved DFR had more than 16 years education compared to about 10% of patients who has less than 12 years of education