plasticity and functional recovery of the brain Flashcards
Plasticity-brain plasticity
The brain would appear to be ‘plastic (not literally - it’s a metaphor!) in the sense that it 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 (Gopnik et al. 1999). 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.
Plasticity-research into plasticity
Eleanor Maguire et al. (2000) 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, 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 Bogdan Draganski et al. (2006) who imaged the brains of medical students three months before and after their final exams. Learning-induced changes were seen to have occurred in the posterior hippocampus and the parietal cortex presumably as a result of the learning.
functional recovery-after brain trauma
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 (spontaneous recovery) and then slow down after several weeks or months. At this point the individual may require rehabilitative therapy to further their recovery.
Functional recovery-what happens in the brain during recovery
The brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage (a bit like avoiding roadworks on the way to school by finding a different route). Secondary neural pathways that would not typically be used to carry out certain functions are activated or unmasked’ to enable functioning to continue, often in the same way as before (Doidge 2007). This process is supported by a number of structural changes in the brain including:
• Axonal sprouting - the growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways.
• Denervation supersensitivity - this 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.
• Recruitment of homologous (similar) areas on the opposite side of the brain. This 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.
Limitation-plasticity-negative plasticity
One limitation of plasticity is that it may have negative behavioural consequences.
Evidence has shown that the brain’s adaptation to prolonged drug use leads to poorer cognitive functioning in later life, as well as an increased risk of dementia (Medina et al. 2007).
Also, 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 (Ramachandran and Hirstein 1998).
This suggests that the brain’s ability to adapt to damage is not always beneficial.
strength-plasticity-age and plasticity
One strength is that brain plasticity may be a life-long ability.
In general plasticity reduces with age. However, Ladina Bezzola et al. (2012) 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 increased 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.
strength-real world application-functional recovery
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.
limitation-functional recovery-cognitive reserve
One limitation of functional recovery is that level of education may influence recovery rates.
Eric Schneider et al. (2014) 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 DFR are less likely to achieve a full recovery.
