plasticity and functional recovery of the brain after trauma

• brain plasticity: the brain's tendency to change and adapt as a result of experience and new learning. this generally involves the growth of new connections
• what happens rapidly after birth?

  the brain experiences a rapid growth in the number of synaptic connections it has, peaking at about 15,000 per neuron at 2-3 years of age (Gopnick et al. 1999)
• what does 'synaptic pruning' mean?

  as we age, rarely-used connections are deleted and frequently used connections are strengthened - a process known as synaptic pruning
• eleanor maguire et al (2000) studied the brains of london taxi drivers and found more volume of grey matter in the posterior hippocampus than in a matched control group
• the posterior hippocampus is associated with the development of spatial and navigational skills in humans and other animals
• london taxi drivers must take a test which assesses their recall of the city streets and possible routes - 'the knowledge'

  maguire et al found that it alters the structure of the taxi drivers brains
• maguire found that the longer the taxi drivers had been in the job, the more pronounced was the structural difference
• bogdan dragranski et al (2006) imaged the brains of medical students 3 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 learning
• the infant brain has twice as many synaptic connections compared to an adult brain
• hyde - plasticity in musicians

  6 year old children receiving instrumental musical training for 15 months compared with children receiving non-musical training
• hyde - plasticity of musicians: findings

  the children receiving instrumental musical training showed changed anatomical features in brain areas known to be involved in the control of playing a musical instrument

  most of these brain areas are part of the cortical motor system but there were also structural changes in the auditory system and corpus callosum
• what can cause brain damage?

  physical trauma

  stroke

  disease or infection

  aging
• physical recovery is not possible after the brain has been damaged - new neurons cannot be made to replace ones that have died
• when one part of the brain dies, unaffected areas of the brain are able to adapt and compensate - another example of brain plasticity (functional recovery)
• functional recovery can occur quite rapidly immediately after trauma (spontaneous recovery). however, the process slows down after a few days or weeks
• axonal sprouting: new nerve endings grow and connect with undamaged nerve cells to form new neuronal pathways
• recruitment of homologous (similar) areas on the opposite hemisphere to do specific tasks e.g if brocas area was damaged then an area on the right might take over
• denervation supersensitivity - this occurs when axons which become aroused to a higher level to compensate for the ones that are lost

  however it can have the negative consequence of oversensitivity to messages such as pain
• P - strength: real world application

  E - processes in plasticity contributed to neurorehabilitation. understanding that axonal growth is possible encourages new therapies to be tried

  E - constraint-induced movement therapy used with stroke patients - they repeatedly practise using affected part of their body (e.g arm) while unaffected arm is restrained

  L - shows research into functional recovery is useful, helps medical professionals know when interventions need to be made
• P - limitation: negative behavioural consequences

  E - evidence shows brains adaptation to prolonged drug use leads to poorer cognitive functioning in later life - and increased risk of dementia

  E - 60-80% of amputees experience unpleasant painful sensations (phantom limb syndrome) due to cortical reorganisation in somatosensory cortex as a result of limb loss

  L - suggests plasticity not always beneficial
• P - strength: plasticity may be a life-long ability

  E - in general, plasticity reduces with age, study demonstrated 40 hours of golf training produced changes in the neural representations of movement in participants aged 40-60

  E - using fMRI, researchers observed increased motor cortex activity in the golfers compared to control group, suggesting more efficient neural representations after training

  L - shows neural plasticity can continue throughout lifespan
• P - limitation: functional recovery - level of education may influence recovery rates

  E - study revealed that the more time people with a brain injury had spent in education the greater their chances of a disability-free recovery DFR

  E - 40% that achieved DFR had 16+ years education compared to 10% that has less than 12 years

  L - implies people with brain damage who have insufficient DFR are less likely to achieve a full recovery