Plasticity and functional recovery of the brain

• the brain is 'plastic' -synaptic connections form and are pruned
• during infancy, the brain experienced a rapid growth in synaptic connections, peaking at about 15,000 at age 2-3.

  as we age, rarely used connections are deleted and frequently used connections are strengthened- synaptic pruning.
• it was one thought that synaptic pruning was limited to childhood. but recent research suggests neural connections can change or be formed at any time, due to learning and experience,
• what studies support the concept of plasticity?

  Maguire et al. and Draganski et al.
• maguire et al:

  found significantly more volume of grey matter in the posterior hippocampus in London taxi drivers than in a matched control group. this part of the brain is linked with the development of spatial and navigational skills

  as part of their training, London cabbies take a complex test called 'the knowledge' to assess their recall of city streets and possible routes. this learning experience appears 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 final exams. learning-induced changes were seen in the posterior hippocampus and the parietal cortex, presumable as a result of the exam
• following trauma, unaffected areas of the brain take over lost functions
• functional recovery of the brain after trauma is an important example of neural plasticity- healthy brain areas take over functions of areas damaged, destroyed or even missing

  neuroscientists suggest this process occurs quickly after trauma (spontaneous recovery) and then slows down- at which point the person may require rehabilitative therapy
• the brain 'rewires' itself by forming new synaptic connections
• 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
• further structural changed during functional recovery may include:

  • axonal sprouting- growth of new nerve endings which connect with other undamaged cells to form new neuronal pathways
  • reformation of blood vessels
  • recruitment of homologous (similar) areas on the opposite side of the brain to perform similar tasks
• strength of plasticity and recovery research: practical application

  understanding processes involved in plasticity has contributed to the field of neurorehabilitation. techniques include movement therapy and electrical stimulation of the brain to counter deficits to cognitive functioning experienced following a stroke. this shows that although the brain may have the capacity to 'fix itself' to a point, the process requires further intervention if it is to be successful.
• limitation: relationship between age and plasticity is complex

  functional plasticity tends to reduce with age. the brain has a greater propensity for reorganisation in childhood as it constantly adapts to new experiences and learning. however, bezzola et al. demonstrated how 40 years of golf training produced changed in the neural representation of movement in participants aged 40-60. this shows that neural plasticity does continue throughout our lifespan
• strength: further support for neural plasticity from animal studies

  hubel and wiesel sewed one eye of a kitten shut and analysed the brain's cortical responses. the area of the visual cortex associated with the set eye was not idle but continued to process information from the open eye. this pioneering study demonstrated how loss of function leafs to compensatory activity in the brain- evidence of neural plasticity
• limitation: neural plasticity may be related to cognitive reserve

  evidence suggests a person's educational attainment may influence how well the brain functionally adapts after injury. schneider et al. found the more time brain injury patients has spent in education (an indication of their cognitive reserve), the greater their chances of a disability-free recovery. this suggests that cognitive reserve is a crucial factor in determining how well the brain adapts after trauma