functional recovery/brain plasticity

what is brain plasticity

• Brain plasticity refers to the brain's ability to change and adapt because of experience and new learning

• The brain continues to create new neural pathways and alter existing ones depending on the experiences we have

• During infancy, brain experiences rapid growth in number of synaptic connections peaking around 2-3 years of age, about twice as many as in adult brain

 

• Nerve pathways (connections between neurons) that are frequently used develop stronger connections, whereas neurons that are rarely/never used eventually die out

• This is synaptic pruning

  • People used to believe that the adult brain was not capable of change but we now know that synaptic pruning allows for lifelong plasticity where new neural connections form in response to new demands - constant adaptation

• Many connections are 'pruned' as we age, resulting in fewer but stronger remaining connections

what is functional recovery

Transfer of functions from a damaged area of the brain after trauma or injury to other undamaged areas

• Existing neurons can grow new axons and dendrites to connect to other neurons to form new synaptic connections - axonal sprouting

• New or existing neurons can also grow to compensate for damaged areas (neural regeneration)

• Neuronal unmasking where dormant synapses open connections to regions of the brain that are not normally activated

• FR can happen spontaneously but then slows down so rehabilitation needed

• Recruitment of similar areas - an undamaged area on the opposite side of the brain performs the specific task

  • Functionality may then resume to the original area (neural reorganisation) - depends on the severity of damage and may not occur

• Denervation super sensitivity - occurs when axons that do a similar job become aroused to a higher level to compensate for the ones that are lost

  • Can have the negative consequence of oversensitivity to messages such as pain

hippocampus info

• Hippocampus is one of the key structures in the limbic system - the limbic system is involved with behaviours that satisfy motivational, learning, and emotional needs including feeding, fighting, escape and mating

• Hippocampus plays important role in laying down new memories, it is found inside each hemisphere of the brain and plays critical role in spatial memory and navigation

• Recent research has shown that lesions to the hippocampus affect individual's ability to remember the location of different places and things

• It is impossible to know whether differences in brain anatomy are predetermined, or whether the brain is susceptible to plastic changes, in response to environmental stimulation

Maguire et al 2000 study procedure

• Participants (experimental group)

  • London taxi drivers were used as ppts since they undergo extensive training, known as 'The Knowledge' (knowing the quickest routes through London's complicated road network - takes around 2 years to master)

  • Made them ideal group for the study of spatial navigation

 

• Aim - to examine whether structural changes could be detected in the brains of people with extensive experience of spatial navigation (London black cab drivers)

  • To establish the neural basis of navigational skills

• Research method

  • Quasi-experiment because IV was whether ppt was London taxi driver or not

  • DV is volume of hippocampi including anterior, body and posterior regions - measured using MRI scans of ppts' brain using two techniques of pixel counting and VBM

  • Researchers were blind to which brain they were looking at

• Method

  • 16 right-handed, healthy, male London taxi drivers participated; all had been driving for more than 1.5 years

    • All right-handed to prevent effects of lateralisation on hippocampal differences

  • Scans of 50 healthy right-handed males who did not drive taxis were included for comparison (VBM analysis) - matched for health, sex, mean age range etc.

    • 16 used for pixel counting

results of study

• Increased grey matter in both right and left hippocampi in the brains of taxi drivers compared with controls (non-taxi drivers)

• Controls had increased grey matter volume in anterior hippocampi than taxi drivers

• Increased volume was found in the posterior (tail bit) part of both hippocampi

• Correlation was also found between amount of time spent as a taxi driver and volume in right posterior hippocampus

  • More time that ppt had been taxi driver, greater volume in right posterior hippocampus

• Functions of various sections of the hippocampi

  • Anterior - learning about new environments

  • Posterior - previously learned information

  • Right hemisphere - mental maps

  • Left hemisphere - memories and events

• Conclusions

  • Regionally specific structural differences between those who drove a London taxi and those who do not

  • Navigational skills required as a London taxi driver are associated with a redistribution of grey matter in the hippocampus

  • The changes in the arrangement of the hippocampal grey matter are acquired due to nurture

  • Findings indicate the possibility of local plasticity in the structure of a normal human brain which allows it to adapt in response to prolonged environmental stimuli

• Reductionist

  • It only examines a single biological factor (size of hippocampi) in relation to spatial memory

  • Fails to take into account other biological and cognitive processes involved in spatial navigation

strengths of plasticity

obvs Maguire et al 2000

more research support

• A similar finding was observed by 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 exam. Finally, Mechelli et al. (2004) also found a larger parietal cortex in the brains of people who were bilingual compared to matched monolingual controls.

age and plasticity

• Functional plasticity tends to reduce with age, brain has greater propensity for reorganisation in childhood as it is constantly adapting to new experiences and learning

• Bezzola et al 2012 - demonstrated how 40 hours of golf training produced changes in neural representation of movement in ppts aged 40-60

  • Using fMRI, researchers observed reduced motor cortex activity in the novice golfers compared to control group suggesting more efficient neural representations after training

  • Neural plasticity does continue throughout the lifespan

• Studies have suggested that abilities commonly thought to be fixed in childhood can still be modified in adults with intense training after traumatic brain injury.

strengths of FR

• Strength - real world application

  • Understanding processes involved in the recovery of abilities has led on to the development of neurorehabilitation.

  • For example, knowledge that axonal growth is possible has encouraged new therapies including constraint induced movement therapy used with stroke patients.

  • Here patients repeat the practice of using the affected part of their body (e.g. an arm) while the unaffected arm is restrained.

  • Helps medical professionals know when interventions need to be made

  • Lead to better quality of life - positive outcome of the theory

Danelli et al. (2013) -

• EB, an Italian boy, was operated on at the age of 2, years to remove a large benign tumour from his left hemisphere.

• virtually all of his left hemisphere was removed, and, at that time, all of his linguistic abilities disappeared too.

• He was right-handed and it seems that his language localisation was in his left hemisphere.

• He underwent an intensive rehabilitation programme and his language abilities started to improve around the age of 5.

• They continued to do so over the next three years to the point that no problems of language ability were reported.

• Danelli et al. (2014) tested him further at the age of 17 to compare his language abilities with 'normal' controls.

  • They found that his right hemisphere had compensated for the loss of the left hemisphere in that he was functioning linguistically well.

  • However, they did find some areas which were not at the expected standard. There were some minor grammatical problems, and he was slower at naming objects in pictures.

• This led the researchers to conclude that the right hemisphere never able to compensate fully.

also Turk 2002 - patient JW (lost ability to talk after damage to left hemi and right fully compensated)

weaknesses of plasticity

• Weakness - negative plasticity

  • Brain's ability to rewire itself can sometimes have maladaptive behavioural consequences

    • Prolonged drug use has been shown to result in poorer cognitive functioning as well as increased risk of dementia later in life (Medina et al 2007)

  • 60-80% of amputees have been known to develop phantom limb syndrome - continued experience of sensations in missing limb as if it were still there

    • These sensations are unpleasant, painful and thought to be due to cortical reorganisation in somatosensory cortex which occurs as a result of limb loss - Ramachandran and Hirstein 1998

weaknesses of F recovery

• Weakness - individual differences may affect the extent to which the brain can do functional recovery

  • Patients with an equivalent of a college education are 7 times more likely than those who did not finish high school to be disability free one year after a moderate to severe traumatic brain injury (Schneider, 2014).

  • This was discovered through gathering retrospective data of over 700 patients where a quarter had achieved disability free recovery (DFR) after one year.

  • Of these:

    • 39% had 16 + years of education

    • 30% had between 12-15 years of education

    • 10% had less than 12 years of education.

weakness - a lot of the evidence of functional recovery comes from case studies

• idiographic, non-generalisable

• lack of baseline knowledge