Plasticity and functional recovery of the brain after trauma

• Functional recovery is when a function is regained after brain damage, because it is transferred from one brain region to another. It is a from of plasticity.
• Plasticity refers to the brain's ability to change and adapt functionally and structurally in response to experience, learning, or injury.
• The key structural changes in the brain during recovery include:

  • Neuronal unmasking
  • Axonal sprouting
  • Reformation of blood vessels
  • Recruitment of homologous areas
• During recovery the brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage.

  • Secondary neural pathways that were inactive before the injury can be reactivated or 'unmasked' to enable functioning to continue, often in the same way as before (Doidge 2007).
• Axonal sprouting is when neurons grow new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways. This bypasses damaged areas.
• Neuronal unmasking is when dormant or inactive synapses become active to compensate for damaged areas.
• Recruitment of homologous areas is when the brain may shift functions to equivalent regions in the opposite hemisphere.

  • An example would be if Broca's area was damaged on the left side of the brain, the right-sided equivalent would carry out its functions.
  • After a period of time, functionality may shift back to the left side.
• Blood vessel formation occurs where there has been damage to the brain. New blood vessels develop around the site of damage to supply nutrients and oxygen to the affected area.

  • This helps promote healing and repair.
• Factors influencing recovery:

  • Age: Younger brains generally recover more effectively due to higher plasticity.
  • Extent of damage: Larger injuries may be harder to compensate for.
  • Rehabilitation: Therapy, including physical, cognitive, or occupational techniques, can enhance recovery.
  • Perseverance and motivation: Personal effort and support systems can impact the speed and extent of recovery.
• Synaptic pruning is when the brain strengthens frequently used neural connections and eliminates weaker ones during development and learning.
• Experience-dependent plasticity is when new experiences, such as learning a skill or adapting to a new environment, can lead to the formation of new neural connections.
• Plasticity occurs throughout life but is more pronounced during childhood (referred to as developmental plasticity). In adulthood, it still happens but at a reduced rate (adaptive plasticity).
• Maguire et al (2000) studied London taxi drivers and compared them to a control group of non-taxi drivers.

  • They aimed to investigate whether extensive experience with spatial navigation (as seen in London taxi drivers) leads to changes in the structure of the brain, specifically the hippocampus.
• In Maguire et al's study all participants underwent MRI scans.

  • The researchers measured the size of the hippocampus, particularly focusing on the posterior (back) and anterior (front) regions.
  • Correlation analysis was conducted between the size of the hippocampus and the amount of time spent as a taxi driver.
• Maguire et al found that the taxi drivers had significantly more volume of grey matter in the posterior hippocampus, meaning they had significantly larger posterior hippocampi compared to the control group.

  • There was a positive correlation between the size of the posterior hippocampus and the number of years spent as a taxi driver.
• Maguire et al's study provides evidence of experience-dependent plasticity, as the hippocampus adapted to meet the demands of spatial navigation.
• Danelli et al examined EB, an Italian boy who underwent surgery at age 2.5 to remove his left hemisphere due to a large tumour.

  • The left hemisphere is typically responsible for language processing.
• Danelli et al found that EB experienced significant language deficits but he received intensive rehabilitation.

  • Over time, his language abilities began to recover. Researchers conducted assessments when EB was 17 years old to evaluate his brain's functional adaptation.
• Danelli et al found that EB's right hemisphere had taken over many of the language functions typically associated with the left hemisphere, such as grammar, vocabulary, and speech production.

  • Although his language was not entirely typical (he had some minor deficits), he could communicate effectively in Italian, his native language.
  • Brain scans showed activity in the right hemisphere during language tasks, highlighting functional recovery through compensation.
• Danelli et al’s case study of EB demonstrates the brain’s ability to adapt and recover from damage, especially during early childhood when plasticity is at its peak.

  • The study supports the idea that the right hemisphere can compensate for extensive damage to the left hemisphere, especially when intervention occurs early.
• A limitation of Danelli et al's study is that it only involved one participant, as it was a case study of a unique case, so it may be difficult to generalise their findings to other individuals with similar conditions.
• A strength of Danelli et al’s study is that it supports the importance of age in recovery. This is because EB was able to recover his language abilities at 17 years old after his left hemisphere was removed at age 2.5. This demonstrates that brain plasticity is high at a younger age, allowing the brain to better reorganise itself.
• A strength of Maguire et al‘s study is that it has high ecological validity. This is because it examined a real-world activity - spatial navigation in London taxi drivers. This means that the findings are more likely to be generalisable to other situations.
• A weakness of Maguire et al’s study is that they couldn’t control participant variables because it was a quasi experiment. This meant that they were unable to randomly allocate because they couldn’t directly manipulate the independent variable as it was naturally occurring. This meant that Maguire couldn’t establish a cause and effect relationship.
• A strength of research into plasticity and functional recovery is that it is supported by robust empirical evidence. For example, Maguire et al. (2000) found that London taxi drivers had larger posterior hippocampi than non-taxi drivers, demonstrating how the brain adapts structurally to the demands of spatial navigation. This strengthens the research as it provides a biological basis for plasticity, highlighting the brain’s ability to rewire itself based on environmental challenges and learning experiences.
• A strength of research into plasticity and functional recovery is that it has practical applications, particularly in neurorehabilitation. Understanding the mechanisms of functional recovery, such as axonal sprouting, has been applied to therapies that aim to enhance brain repair after trauma. For example, stroke patients may undergo intensive physical or cognitive therapy to promote recovery by encouraging dormant pathways to become active. This strengthens the research as it can lead to positive outcomes, such as enhancing the quality of life of individuals who have experienced brain damage.
• A limitation of research into plasticity and functional recovery is the reliance on animal studies in some investigations of neuroplasticity, raising ethical concerns. Hubel and Wiesel (1963) study involved sewing one eye of a kitten shut and analysing the brain’s responses. Subjecting animals to invasive procedures can be considered to be unethical due to the trauma they experience and are unable to consent to. This weakens the research as it is hard to justify the findings due to the harm caused to animals.