Lesson 9 - Plasticity and functional recovery

Question 1

What is plasticity?

Answer 1

The ability of the brain to adapt and change synaptic routes in light of learning or damage to areas of the brain

Question 2

Plasticity in a new born brain

Answer 2

It is the most fascinating time to study plasticity, as there are more neurons by the end of the first year of life than there will be when it is fully mature. This is because the brain is developing and it is exposed to a vast range of experiences and stimuli. Therefore there is a lot of plasticity due to learning.

An example of this is Villablanca and Hovda (2000) who found that if an infant with a severely damaged hemisphere at birth has it removed, they will show very few, if any, cognitive impairments as an adult

Question 3

Plasticity as a result of life experience

Answer 3

There is a natural decline in cognitive function with age. Boyke et al (2008) wanted to find a way to reverse this. He found that if 60 year olds were taught a new skill like juggling, they found an increase in grey matter in the visual cortex, showing evidence for plasticity. However these changes reversed once the practice stopped

Question 4

Plasticity and meditation

Answer 4

Meditation has been found to encourage plasticity and internal brain function

Davidson et al (2004) compared 8 Tibetan monks who regularly meditated with 10 student volunteers who had no previous experience. They were fitted with electrodes and they picked up much greater activation of gamma waves – which control neutron activity – than in the student volunteers, who had a slight change in activity. This shows that meditation can change the workings of the brain for the short and long term, further showing how plasticity in the brain works

Question 5

Strengths of plasticity

Answer 5

Research support from animal studies

• Kempermann et al (1998) found that rats kept in complex environments had an increased amount of new neurons compared to rats housed in ordinary cages. In particular there were an increase in neurons in the hippocampus which controls functions like memories and navigation.
• Blakemore and Mitchell (1973) conducted a study on the visual cortex in cats. They found that visual neurons could be changed by exposure to specific environments soon after birth. Cats raised in an environment with black vertical stripes did not respond to horizontal stripes. This shows that exposure to stimuli have an effect on the workings of the brain. This is hard to generalise to humans because babies are not raised in one kind of environment

Research from human studies

• Maguire et al (2000) studied London taxi drivers against a control group of able drivers who did not drive taxis. Using MRI scans, they found that the frontal hippocampus was larger in the taxi drivers compared to the control group. This is because the hippocampus has a prominent role in spatial navigation. There was also a positive correlation between the size of the hippocampus and the time spent driving taxis.

Question 6

Weaknesses of plasticity

Answer 6

• Medina et al (2007) found that behaviour can have negative consequences on plasticity, such as adaptations to prolonged drug use can lead to impaired cognitive function later in life and an increased risk of dementia. Therefore plasticity is not always beneficial.
• You cannot always generalise animal studies to humans. Humans have a much higher level of cognitive function compared to rats and cats. They are also mobile from birth, meaning the brain will develop much faster
• There are ethical issues in Blakemore and Mitchell’s study, as the kittens were deprived of a normal environment to be raised in and this is ethically incorrect

Question 7

Plasticity as a result of brain trauma

Answer 7

Functional recovery is the transfer of neurons from a damaged area of the brain to a healthy area of the brain. This is so the function of that area can be compensated for.

Someone might experience blows of missile wounds like bullets to the brain, a haemorrhage or stroke or viral disease.

Question 8

How does function recovery happen?

Answer 8

Axonal sprouting – new nerve endings grow and these connect with other undamaged nerve cells, forming new neuronal pathways

Denervation supersensitivity – undamaged neurons that carry out a similar role to the damaged ones become hypersensitive in order to compensate for the ones that are lost.

Recruitment of homologous (similar) areas – if an area on the left hemisphere is damaged, for example, the left portion of the Broca’s area, the right side would carry out its function.

Neuronal unmasking – Wall (1977) found dormant synapses in the brain, but their functions were blocked. However increased rate of input to these synapses which could occur as a result of damage to surrounding areas could lead to these synapses unmasking and creating new pathways.

Question 9

Danelli et al (2013)

Answer 9

Laura Danelli studied a boy called EB, who underwent a surgery to remove a benign (non-harmful) tumour in the left hemisphere. As a result, he lost all linguistic abilities. His language started to improve by age 5 as a result of rehabilitation. By age 8, he had little to no linguistic difficulties. When he was tested at age 17, they found that his right hemisphere had taken over the linguistic functions of the left hemisphere. This supports the idea of recruitment of homologous areas

Question 10

Strengths of functional recovery

Answer 10

• It has contributed to the field of neuro-rehabilitation. While functional recovery can happen naturally, forms of active intervention can help it maintain improvements. Neuro-rehab can involve therapy and electrical stimulation which can help overcome the deficits to motor and cognitive function after trauma
• Schneider et al (2014) found that patients with a college education or equivalent are 7 times more likely to recover and be disability free one year after a moderate or severe brain trauma compared to those who did not finish high school. Researchers found that ‘cognitive reserve’ which is the brains ability to withstand damage is associated with higher educational achievement.

Question 11

Weaknesses of functional recovery

Answer 11

• Huttenlocher (2002) found that due to the widely accepted fact that functional recovery and plasticity weakens with age (Huttenlocher states that this is due to synaptic pruning), recovery from trauma past childhood should be with behavioural measures like social support. Adults require much more extended retraining in order to produce change
• Ratcliffe et al (2007) examined 325 patients aged 16-45 who had brain trauma for their level of recovery and found that women performed significantly better on tests of attention/working memory and language, whereas men performed better in visual analyst skills. Therefore you cannot generalise certain areas of recovery across both genders