Plasticity and functional recovery of the brain after trauma

• Plasticity


  Brain plasticity - brain is 'plastic' in sense it has ability to change throughout life

  Infancy brain experiences rapid growth in number of synaptic connections it has peaking at about 15,000 per neuron at 2-3 years of age, rarely used connections are deleted and frequently used connections are strengthened - synaptic pruning.

  Synaptic pruning enables lifelong plasticity where new neural connections are formed in response to new demands on the brain.
• Research into plasticity

  Maguire studied brains of London taxi drivers, found significantly more volume of grey matter in posterior hippocampus than in matched control group - this part of brain associated with development of spatial and navigational skills

  As part of training cab drivers must take complex test which assess their recall of the city streets and possible routes

  Maguire found this learning experience alters structure of taxi drivers brains, they also found longer taxi drivers been on job, more pronounced the structural difference (positive correlation)
• Draganski imaged brains of medical students three months before and after their final exams learning induced changes were seen to have occurred in posterior hippocampus and parietal cortex as result of learning
• Functional recovery after brain trauma


  Unaffected areas of brain often able to adapt and compensate for those areas that are damaged

  Functional recovery that may occur in the brain is example of neural plasticity

  Healthy brain areas may take over the functions of areas that are damaged destroyed or missing.

  Neruoscientists suggest this process can occur quickly after trauma (spontaneous recovery) and then slow down after several weeks or months, at this point individual may require rehabilitative therapy to further their recovery.
• What happens in brain during recovery

  Brain rewires and reorganises self by forming new synaptic connections close to area of damage, secondary neural pathways that wouldn't typically be used to carry out certain functions are activated or unmasked to enable functioning to continue often in same way as before - process supported by number of structural changes in brain including:
• • Axonal sprouting - growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways
  • Denervation supersensitivty - occurs when axons that do a similar job become aroused to higher level to compensate for ones that are lost, however, can have negative consequence of oversensitivity to messages such as pain.
  • Recruitment of homologous(similar) areas on opposite side of brain - eg if Broca's area damaged then right side would carry out it'd functions
• real world application - S- functional recovery

  contributed to field of neurorehabilitation, understanding axonal growth encourages new therapies to be tried

  eg constraint induced movement therapy used with stroke patients where they repeatedly practice using affected part of their body while unaffected part is restrained.

  --> useful
• Negative plasticity - W - plasticity

  Negative behavioural consequences - brains adaptation to prolonged drug use leads to poorer functioning in later life and increased risk of dementia

  60-80% amputees develop phantom limb syndrome - continued experience of sensations in missing limb as if it was still there - unpleasant, painful due to cortical reorganisation in somatosensory cortex occurring as result of limb loss

  --> not always beneficial
• W - Functional recovery


  level of education may influence recovery rates

  Schneider et al revealed that more time people with brain injury had spent in education - taken as indication of their cognitive reserve - greater their chance of a disability free recovery

  40% those who achieved DFR had more than 16 years education compared to 10% had less than 12 years education

  --> imply people with brain damage who have insufficient cognitive reserve are less likely to achieve a full recovery.