5. Plasticity of the brain

• Plasticity

  • The ability of the brain to adapt to new experiences
  • During infancy, the brain increases the number of synaptic connections, peaking at about 15,000 per neuron at 2-3 years old
  • Synaptic pruning - as we age, rarely-used connections are deleted and frequently used connections are strengthened
  • This enables life long plasticity where new neural connections are formed in response to new demands on the brain
• Research into plasticity

  • Maguire et al. studied the brains of London taxi drivers and found significantly more volume of grey matter in the posterior hippocampus compared to a control group
  • This part of the brain is associated with navigational and spatial skills
  • Found that taxi learning experience alters the structure of their brains and the longer they had been in the job, the more pronounced a difference - positive correlation
• Functional recovery

  • Connections regrow and strengthen again after damage such as trauma or illness
  • Example of neural plasticity
  • Neuroscientists suggest that this process can occur quickly after trauma then slow down after several weeks or months. At this point the individual may require rehab therapy to further their recovery
• What happens in the brain during recovery?

  • Secondary neural pathways that would not typically be used to carry out certain functions are activated to enable functioning to continue
  • Axonal sprouting - undamaged axons grow new nerve endings to reconnect injured neurons
  • Denervation supersensitivity - axons that complete a similar job become aroused to a higher level to compensate for those lost. It can have the negative consequence of oversensitivity to messages such as pain
  • Recruitment of homologous areas - regions on opposite sides of the brain take on functions of damaged areas
• AO3 - Plasticity wide range of research

  • Maguire et al. taxi driver study
  • This suggests that due to the plasticity of the brains, this learning experience alters the structure of the taxi drivers’ brains. Additionally, as posterior hippocampal volume was positively correlated with the amount of time they spent as a taxi driver, this indicates that the highest levels of plasticity were evidence in those with more extensive experience.
• AO3 - Plasticity research support

  • Draganski et al. (2006) who imaged the brains of medical students three months before and after their final exams. Changes were seen in the posterior hippocampus and the parietal cortex. Can be seen to be another benefit of the brain’s ability to change and adapt as a result of experience and new learning
  • The availability of wide range of supporting research for the existence of plasticity  provides clear evidence of the brain's ability to change as a result of experience, suggesting this concept has very strong scientific credibility
• AO3 - Plasticity negative plasticity

  • Medina et al. (2007) found that the brain’s adaptation to prolonged drug use leads to poorer cognitive functioning and an increased risk of dementia later in life
  • Ramachandran (1998): 60-80% of amputees have been known to develop phantom limb syndrome which causes sensations that are usually unpleasant and painful. The continued experience of these unpleasant sensations are thought to be due to cortical reorganisation in the somatosensory cortex that occurs as a result of limb loss
  • Does not support denervation supersensitivity
• AO3 - Plasticity and age

  • Bezzola et al. demonstrated how 40 hours of golf training in pps aged 40-60 resulted in an increase of activity in the motor cortex in the novice golfers compared to a control group. This shows that the ability of the brain to learn and adopt to new experiences, even later in life
  • Neural plasticity can continue throughout the lifespan which has an increasingly more relevant real-world value with an aging population. This seemingly lifelong ability can be used to improve the lives those people who are living for longer periods of time
• AO3 - Functional recovery has real world application

  • CIMT is used with stroke patients, for instance, if there is a loss of function on side (e.g. left arm), then they repeatedly practise using this affected part of their body, whilst the unaffected body part is restrained. The use CIMT produces cortical reorganisation and axonal growth which results in regained or improved function.
  • Contributed to the field of neurorehabilitation as research into functional recovery allows medical professionals to know when interventions need to be made and encourages new therapies to be tried
• AO3 - Functional recovery concerns with methodology

  • Banerjee et al. (2014) treated 5 people (no control group) who had a severe type of ischemic stroke that affects a large part of the brain (TACS) with stem cells. All pps in this trial recovered compared to the more typical 4% recovery level
  • Small sample sizes are known to make effective genealistions to whole populations very problematic
  • The lack of control group means that we were unable to compare stem cell treatment with a matched group who receive different treatment
• AO3 - Functional recovery and educational attainment

  • Schneider et al. (2014) found that the more time people with a brain injury had spent in education - taken as an indication of their ‘cognitive reserve’  - the greater their chances of a disability-free recovery (DFR).  For instance, 40% of those who had DFR had more than 16 years’ education compared to 10% of those who had less than 12 years’ education
  • ‘Cognitive reserve’ that is associated with greater educational attainment was an important  factor in neural adaptation during recovery from a traumatic brain injury