Plasticity & Functional Recovery of the Brain after Trauma (2)

What is neuroplasticity ?

• Neuroplasticity refers to the brain’s ability to adapt to change, be that from injury, damage due to illness or changes brought about due to learning and experience

What is structural plasticity ?

• Structural plasticity refers to changes within brain structures e.g.

  • increased grey matter build-up in the posterior hippocampusdue to learning experienced over time

    • Such changes do not happen immediately, they develop slowly, in response to either the degree of damage or the extent of the learning/experience

    • The buildup of grey matter is due to the increased synaptic connectedness in the brain regions involved

What is plasticity ?

• Plasticity means that the brain is not a static, concrete mass; it is a flexible organ that responds and adapts to environmental stressors/stimuli

Examples of neuroplasticity

• London black cab taxi drivers spend years navigating and learning routes through central London

  • Their brains adapt by increasing grey matter in the posterior hippocampus, a brain region linked to spatial navigation (Maguire et al.2000)

• People who learn a juggling routine show increased grey matter in the mid-temporal cortex compared to non-jugglers

  • Once the juggling participants had ceased juggling for three months the grey matter linked to juggling began to decrease (Draganski et al. 2004)

  • The jugglers' brains thus showed evidence of neuroplasticity and neural pruning (the loss of grey matter)

• People who practice mindfulness show increased grey matter in the prefrontal cortex and decreased grey matter in the amygdala

  • The participants in this study reported a decrease in stress and anxiety symptoms (Gotink et al. 2016)

What is functional plasticity ?

• Functional plasticity (also known as functional recovery) refers to the brain’s ability to replace lost or damaged functions by using existing brain regions in their place

  • Functions such as mobility, memory and language are taken over by healthy brain regions capable of replacing the lost functionality

  • Functionality may never be 100% what it was before the loss but it serves as a good 'stand-in' when circumstances dictate

    • One example involves a child who had half of her brain removed (hemispherectomy) to control her epilepsy; she can function almost completely normally after surgery as her remaining hemisphere takes over the tasks of the hemisphere which have been removed

Key Structural Changes

• Axonal sprouting

  • New growth of nerve endings from surviving neurons

  • These fibres link up with other undamaged cells to form alternative neural circuits

• Reformation of blood vessels

  • Damaged tissue stimulates angiogenesis, restoring oxygen and nutrient supply to recovering areas

• Recruitment of homologous areas

  • Regions in the opposite hemisphere (the “mirror image” area) adopt functions of injured zones

  • E.g., if Broca’s area (speech production) in the left hemisphere is damaged, the right-side equivalent may compensate over time

• Neural (Synaptic) pruning

  • Use-dependent refinement: Synapses that are used frequently grow stronger; unused ones are “cleared out”

  • This pruning makes the network leaner and more efficient both structurally and functionally

  • As seen in Draganski’s study, learning-induced growth is followed by selective pruning of excess connections

Examples of functional recovery

• Danelli et al. (2013) conducted a case study of E.B., a 14-year-old boy with brain damage

  • At 2 years old, EB had to have a hemispherectomy on the left side of his brain to remove a tumour 

  • His language centres were removed, including Broca's and Wernicke's areas

  • Immediately after surgery, EB lost all language function

  • However, after two years, EB had recovered his language ability, even without his left hemisphere 

    • fMRI scans showed that the right hemisphere was acting as if it was the left hemisphere in terms of language function

• The case of E.B. demonstrates functional recovery

  • The brain can adapt and recover after trauma

  • Functional recovery has something of a 'time stamp'

    • If the recovery takes place early in life the affected person has a chance of almost full recovery

    • For older people, this is less likely due to the ageing of the brain and a decrease in synaptic activity

• Functional recovery tends to begin with a rapid growth spurt then slow down and eventually plateau after some time

  • This should be reflected in the rehabilitative therapy that is given to patients with brain damage

Strength 1 Evaluation of plasticity & functional recovery

• There is an impressive body of research into neuroplasticity, with findings supporting the idea that the brain adapts to change

  • If several different studies come to the same conclusion (in terms of neuroplasticity) then the theory has good internal validity

  • This means that researchers can exclude other explanations for their findings

Strength 2 Evaluation of plasticity & functional recovery

• There are huge practical applications for both structural plasticity and functional recovery

  • Understanding the brain's capacity to compensate for loss and being aware of the slowing-down phase of functional recovery are key to informing therapy - both physical and cognitive - for patients with brain damage

Limitation 1 Evaluation of plasticity & functional recovery

Neuroplasticity and functional recovery do not always happen when needed e.g.

• The case of H.M. who had his hippocampus removed at the age of 27

  • H.M. suffered from catastrophic anterograde amnesia

  • He never recovered any functionality: his memory (particularly short-term memory) was affected permanently

  • This casts doubt as to the universality of plasticity - it does not apply in every case

Limitation 2 Evaluation of plasticity & functional recovery

• Research in this field is correlational only

  • This means that cause-effect cannot be established

  • This is a limitation as it leaves too many unanswered questionse.g.

    • why does grey matter build up in specific brain regions?

    • what other possible factors could account for the grey matter?

    • how can cause-effect be found when the sample sizes used in the research are generally so small (e.g. Maguire only used 16 taxi driver participants)?