4. plasticity & functional recovery Flashcards
The brain has the ability to change throughout life.
During infancy, 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 this is about twice as many as there are in the adult brain. As we age, rarely used connections are deleted and frequently used connections are strengthened - a process known as
synaptic pruning.
People once thought that the adult brain was not capable of change, but we now understand that synaptic pruning enables
lifelong 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 than in a matched control group.
This part of the brain is associated with the development of spatial and navigational skills in humans and other animals.
As part of their training, London cabbies must take a complex test called ‘The Knowledge test’, which assesses their recall of the city streets and possible routes. Maguire et al. found that this learning experience
alters the structure of the taxi drivers’ brains. They also found that the longer the taxi drivers had been in the job, the more pronounced was the structural difference (a positive correlation).
A similar finding was observed by Draganski et al. who imaged the brains of medical students three months before and after their final exams and found
learning-induced changes in the posterior hippocampus and the parietal cortex, presumably as a result of the learning.
AO3: strength of plasticity
research support - bezzola (golfers)
One strength is that brain plasticity may be a life-long ability.
In general plasticity reduces with age. However, Bezzola et al. demonstrated how 40 hours of golf training produced changes in the neural representations of movement in participants aged 40-60. Using fMRI, the researchers observed reduced motor cortex activity in the novice golfers compared to a control group, suggesting more efficient neural representations after training.
This shows that neural plasticity can continue throughout the lifespan.
AO3: limitation of plasticity
NEGATIVE PLASTICITY
One limitation of plasticity is that it may have negative behavioural consequences.
60-80% of amputees have been known to develop phantom limb syndrome - the continued experience of sensations in the missing limb as if it were still there. These sensations are usually unpleasant, painful and are thought to be due to cortical reorganisation in the Somatosensory cortex that occurs as a result of limb loss.
This suggests that the brain’s ability to adapt to damage is not always beneficial.
Following physical injury, or other forms of trauma such as the experience of a stroke, unaffected areas of the brain are often able to adapt and compensate for those areas that are damaged. The functional recovery that may occur in the brain after trauma is an example of neural plasticity.
Healthy brain areas
may take over the functions of those areas that are damaged, destroyed or even missing. Neuroscientists suggest that this process can occur quickly after trauma.
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1 . The brain is able to rewire and reorganise itself by forming
NEW SYNAPTIC CONNECTIONS close to the area of damage.
2 . SECONDARY NEURAL PATHWAYS that
would not typically be used to carry out certain functions are activated or ‘unmasked’ to enable functioning to continue
3 . the growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways:
AXONAL SPROUTING
4 . DENERVATION SUPERSENSITIVITY
occurs when axons that do a similar job 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.
5 . RECRUITMENT OF HOMOLOGOUS AREAS on the opposite side of the brain - means
that specific tasks can still be performed. 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 then shift back to the left side.
AO3: strength of functional recovery
REAL-WORLD APPLICATION -constraint induced movement theraphy
One strength of functional recovery research is its real-world application.
Understanding the processes involved in plasticity has contributed to the field of neurorehabilitation. Simply understanding that axonal growth is possible encourages new therapies to be tried. For example, constraint-induced movement therapy is used with stroke patients whereby they repeatedly practise using the affected part of their body (such as an arm) while the unaffected arm is restrained.
This shows that research into functional recovery is useful as it helps medical professionals know when interventions need to be made.
AO3: limitation of functional recovery
COGNITIVE RESERVE - Schneider (education levels)
One limitation of functional recovery is that level of education may influence recovery rates.
Schneider revealed 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). 40% of those who achieved DFR had more than 16 years’ education compared to about 10% of those who had less than 12 years’ education.
This would imply that people with brain damage who have insufficient cognitive reserves are less likely to achieve a full recovery.
