L9 - Plasticity & Functional Recovery Of The Brain After Trauma

Question 1

Plasticity

Answer 1

• refers to the ability of the brain to change and adapt synapses, pathways, and structures in light of various experiences.
• Those experiences are usually positive
  E.g. learning and memory involve brain plasticity, in that memory involves changes to brain synapses and pathways.
• plasticity can also involve the ability of the brain to adapt to damage caused by trauma.
  -Recovery of function lost after brain damage (functional recovery) is currently a key area of neuroscience research.

Question 2

Different types of plasticity

Answer 2

• in the new-born brain
• as a result of life experience
• meditation

Question 3

Plasticity in the new-born brain

Answer 3

• the first year of a baby’s life is the most important time to study plasticity as it’s been shown that by the end of the first year, the brain actually has more neurons and more synapses than it will have when it becomes fully mature in late adolescence/early adulthood
• this may be as the brain needs more neurons that needed in the first years of life is simply because the developing brain is exposed to a vast range of experiences, environment and stimuli.
• The brain has a lot to learn and a lot to do – hence the brain has much more plasticity during this period
• The most extreme example of how the brain has plasticity in the early infanthood was shown by research into hemispherectomy – very occasionally a baby is born with one hemisphere severely damaged either through a genetic problem, illness or a difficult birth.
• It has been found that if that whole hemisphere is removed soon after birth, then as an adult that person shows few, if any behavioural or cognitive impairments (Villablanca and Hovda, 2000)

Question 4

Plasticity as a result of life experience

Answer 4

• As people gain new experiences, nerve pathways that are used frequently develop stronger connection.
• However, there is a natural decline with in cognitive functioning with age that can be due to changes in the brain.
• researchers looked into ways into which new connections can be made to reverse this effect.
• Boyke et al (2008) found evidence of brain plasticity in 60 year olds taught a new skill – juggling.
• They found increase in grey matter in the visual cortex. Interestingly, when juggling practise stopped, these changes were reversed

Question 5

Plasticity & meditation

Answer 5

• Researchers working with Tibetan monks have been able to demonstrate that meditation can change the inner workings of the brain and thus increase plasticity.
• Davidson et al (2004) compared eight practitioners of Tibetian meditation with 10 student volunteers with no previous meditation experience.
• Both groups were fitted with electrical sensors and asked to meditate for short periods.
  -The electrodes picked up much greater activation of gamma waves (which coordinate neuron activity) in the monks. The students showed only a slight increase in gamma wave activity while meditating.
• The researchers concluded that meditation not only changes the workings of the brain in the short term, but may also produce permanent changes, based on the fact that the monks had far more gamma wave activity than the control group.

Question 6

Evaluation of plasticity

Answer 6

strengths
- research support from animal studies - kempermann et al. (1998), Blakemore & Mitchell (1973)
- research support from humans - Maguire (2000)
- age differences in plasticity
weaknesses
- Negative Plasticity
- Generalisation issues in animals when studying plasticity
- ethical issues in animals when studying plasticity

Question 7

Kempermann et al. (1998)

Answer 7

• found an increased number of new neurons for rats housed in complex environments compared to rats housed in ordinary cages.
• Also, the rats in the complex environments showed an increase in neurons in the hippocampus – a part of the brain associated with new memories and the ability to navigate from one location to another.
• This study therefore shows brain plasticity with regards to the hippocampus.

Question 8

Blakemore & Mitchell (1973)

Answer 8

• studying the development of the visual cortex in cats.
• They were able to show that the characteristics of visual neurons were (or could be) permanently changed by exposure to specific environments soon after birth.
• Kittens reared in an environment with black vertical stripes did not respond to horizontal - black stripes. This shows how exposure to certain stimuli affects brain development.
• However, because this study was carried out on cats it might be an issue to generalise this to humans since human babies are not raised in only one type of environment (e.g. being exposed to only vertical stripes)

Question 9

Maguire et al (2000)

Answer 9

• studied London taxi drivers to discover whether changes in the brain could be detected as a result of their experience of spatial navigation.
• Using an MRI scanner, the researchers calculated the amount of grey matter in the brains of taxi drivers and a compared to a set of control participants.
• They found that the front part of the hippocampus was larger than controls and this was positively correlated to how long they had spent driving taxis. This study shows how brain plasticity is evident in taxi drivers.

Question 10

Age differences in plasticity

Answer 10

• Although brain plasticity tends to reduce with age, the brain has greater propensity for reorganisation in childhood as it is constantly adapting to new experiences and learning.
• However, studies have shown the plasticity can occur in older people too.
  E.g. Bezzola et al (2012) demonstrated how 40 hours of golf training produced changes in the neural representation of movement in participants aged 40-60.
• Using fMRI scans, the researchers found reduced motor cortex activity before the training commenced but after training, motor cortex activity seemed to have increased.
• This study does show that plasticity can occur in older people. This is a strength as Bezzola’s study has shown that there is no age limit to brain plasticity showing that all age groups can improve their brain capacity.

Question 11

Negative plasticity

Answer 11

• 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 increased risk of dementia (Medina et al. 2007).
• This shows that brain plasticity is not always beneficial and can have negative consequences.

Question 12

Generalisation issues in animals when studying plasticity

Answer 12

• there is a major problem with studies carried on animals e.g. kittens and rats when studying brain plasticity.
• Both these animal species are completely different to humans.
  E.g. baby rats and kittens are mobile from birth which means that the brain development of these animals will be much faster whereas human babies are not mobile at birth meaning their brain development will be much slower.
• This means we should be cautious when we apply the findings of animal studies to human brain plasticity.

Question 13

Ethical issues when studying plasticity

Answer 13

• studies carried on rats and kittens when studying brain plasticity are ethically questionable.
  E.g. the kittens in Blakemore and Mitchell’s study were only exposed to an environment with vertical stripes – this is questionable as the kittens were denied a normal environment – this means that ethically the study was not correct.
• Therefore we cannot apply the findings to human plasticity since humans are not denied their normal environment.

Question 14

Functional recovery after brain trauma

Answer 14

• the transfer of functions from a damaged area of the brain after trauma to other undamaged areas in the brain

Question 15

Common types of brain trauma

Answer 15

• Physical trauma e.g. blows and missile wounds (e.g. a bullet) to the skull and brain
• Cerebral haemorrhage – e.g. a stroke - when a blood vessel in the brain bursts; brain areas supplied by the blood vessel begin to die, while the pressure of the blood released into brain tissue can also cause damage
• Cerebral ischaemia: e.g. a stroke - this is when a blood vessel in the brain is blocked, for instance by a blood clot (thrombosis) or by the thickening of the blood vessel walls through fatty deposits (arteriosclerosis); brain areas supplied by the blood vessel begin to die
• Viral or bacterial infections e.g. meningitis – these can destroy brain tissue

Question 16

What does brain trauma affect?

Answer 16

• virtually all areas of behaviour and cognition
• can lead to movement paralysis, language problems (aphasia), memory problems (amnesia), or difficulties in perception.
• the blood supply to the brain is lateralized within one hemisphere or the other, strokes are often lateralized to one hemisphere. This means that the behavioural effects are likely to be one sided.
  E.g. a left hemisphere stroke may lead to paralysis on the right side of the body. It may also affect language, as this is controlled by the left hemisphere

Question 17

What happened in the 1960’s?

Answer 17

• researchers studied stroke victims who were able to regain functioning.
• discovered that when brain cells are damaged during stroke, the brain re-wires itself over time so that some level of function can be regained.
• other parts of the brain seem to take over the functions of the parts of the brain that have been destroyed or damaged.
• Neurons next to the damaged brain areas can form new circuits that resume some of the lost function.

Question 18

What happens to the brain naturally in recovery?

Answer 18

• The brain is able to rewire and reorganise itself by forming new synaptic connections close to the area of damage.
• 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).
• process is supported by structural changes in the brain

Question 19

Structural changes in the brain

Answer 19

• axonal sprouting
• denervartion supersensitivity
• recruitment of homologous (similar) areas
• neuronal unmasking

Question 20

Axonal sprouting

Answer 20

• Axonal sprouting the growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways

Question 21

Denervation supersensitivty

Answer 21

• Denervation supersensitivity this occurs when axons that do a similar 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

Question 22

Recruitment of homologous (similar) areas

Answer 22

• Recruitment of homologous (similar) areas on the opposite side of the brain to perform specific tasks.
E.g. 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

Question 23

Neuronal unmasking

Answer 23

• Wall (1977) first identified ‘dormant synapses’ in the brain.
• This means the synaptic connections exist but their functions are blocked.
• However, increasing the rate of input to these synapses which could happen when surrounding brain area(s) is damaged can then open (unmask) these dormant synapses.
• This unmasking of dormant synapses can open connections to regions of the brain that are not normally activated creating a lateral spread of activation which then gives way to the development of new structures.

Question 24

Study to support functional recovery

Answer 24

• Danelli et al (2013) studied an Italian boy named EB who was operated on at the age of 2.5 years to remove a large benign tumour from his left hemisphere.
• After the operation, EB lost all his linguistic abilities, He was right handed and therefore his language was probably located in the left hemisphere.
• He underwent an intensive rehabilitation programme and his language abilities started to improve at age 5. They continued to do so over the next three years to the point when he no longer had any language difficulties.
• When they tested him at age 17 compared to ’normal’ controls, they found that his right hemisphere had compensated for the loss of the left hemisphere and that his linguistic abilities were functioning well.
• This study supports the idea of functional recovery in the recruitment of homologous areas (on the opposite side of the brain e.g. EB’s right hemisphere compensating for the damage to the left hemisphere.)

Question 25

Evaluation of functional recovery after trauma

Answer 25

• practical application
• age differences in functional recovery
• educational attainment & functional recovery
• gender differences in functional recovery

Question 26

Practical application

Answer 26

• one strength of understanding the processes involved in functional recovery is its practical application.
• It has contributed to the field of neuro-rehabilitation.
• Although recovery does happen naturally, spontaneous recovery tends to slow down after a number of weeks so forms of physical therapy may be required to maintain improvements in functioning – this is when neuro-rehabilitation can occur which is when doctors provide therapy and electrical stimulation of the brain to counter the deficits in motor and/or cognitive functioning that may have been experienced following a stroke for example.
• This shows that functional recovery may be natural and fix itself to a point but may require further intervention to be successful.

Question 27

Age differences in functional recovery

Answer 27

• It is the commonly accepted view that functional recovery after brain trauma reduces with age (Huttenlocher, 2002).
• According to this view, the only option following traumatic brain injury beyond childhood is to develop compensatory behavioural strategies to work around such a deficit (such as social support or developing strategies to deal with cognitive deficits).
• However, studies have suggested that even abilities commonly through to be foxed in childhood can still be modified in adults with intense retraining.
• Despite these indications of adult plasticity, Elbert et al (2001) conclude that the capacity for neural reorganisation is much greater in children than adults as shown by the extended practice that adults require in order to produce changes.

Question 28

Educational attainment & functional recovery

Answer 28

• Research suggests that education has an effect on functional recovery.
  E.g. Schneider et al (2014) found that patients with the equivalent of a college education are seven times more likely to recover and be disability free one year after a moderate to severe brain trauma compared to those not finishing their high school education.
• The researchers concluded that ‘cognitive reserve’ (associated with greater educational attainment) could be a factor in neural adaptation during recovery after traumatic brain injury – in other words the longer the time spent in education had a direct relationship with functional recovery after trauma. - Schneider’s findings therefore suggest that we should encourage our young generation to complete their education as this would help them recovering from any brain injury (including stroke) simply because their nerve fibres would be able to regenerate.

Question 29

Gender differences in functional recovery

Answer 29

• There is research to suggest that women recover better from brain injury as their function is not as lateralised as men.
  E.g. Ratcliffe et al (2007) examined 325 patients with brain trauma for their level of response for cognitive skills to rehabilitation.
• The patients were 16-45 years old at injury, received rehabilitation at a care facility, and completed a follow-up one year later. It was found that women performed significantly better than men on tests of attention/working memory and language whereas men outperformed females in visual analytical skills.
• Overall, the results suggested a better recovery for women although the results did not control for performance pre-injury, so this could have influenced results.