Brain Plasticity

Plasticity: the brain's tendency to change and adapt in response to a new experience or new learning

During infancy, the brain experiences rapid growth of new synaptic connections, peaking at about 3 years old.
As we age, rarely used connections are deleted while frequent connections are strengthened - a process known as synaptic prunning.

Maguire et al
studied the brains of London taxi drivers and found significantly more volume of grey matter in the posterior hippocampus than in the matched control group. This part of the brain is associated with the development of navigational and spatial skills.

Draganski et al imaged the brains of medical students before and after their final exams. He found learning-induced changes in the posterior hippocampus and the parietal cortex

Mechelli et al found a larger parietal cortex in the brains of people who were bilingual opposed to people who spoke one language.

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Functional Recovery of the Brain After Trauma

Functional recovery is a form of plasticity; following damage through trauma, it is the brain's ability to redistribute or transfer functions usually performed by damaged areas to undamaged areas.

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 to enable functioning to continue, often in the same way as before

This process is supported by a number of structual changes in the brain
Anoxal sprouting: the growth of new nerve endings which connect with other undamaged nerve cells to form new neuronal pathways
Reformation of blood vessels
Recruitment of similar areas on the opposite side of the brain to perform similar tasks

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Evaluation of Plasticity and Functional Recovery

Practical Application
Following trauma, the brain's 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 shows that the brain can fix itself to a point

Negative Plasticity
Brain's ability to rewire itself may lead to malabdaptive behavioural consequences. Medina et al found prolonged drug use results in poorer cognitive functioning as well as an increased risk of dementia later in life. Also 60-80% of amputees develop phantom limb syndrome which is the continued feeling of sensation in a missing limb which are usually painful and thought to be due to cortical reorganisation of the somatosensory cortex.

Age and Plasticity
Functional plasticity tends to reduce with age. That said, Bezzola et al demonstrated how 40 hours of golf training produced changes in the neural representation of movement in the 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.

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Hemispheric Lateralisation

Hemispheric lateralisation is the idea that the two halves of the brain are functionally different and that certain mental processes and behaviours are mainly controlled by one hemisphere rather than the other.

Split Brain Studies
Sperry's studies involve a unique group of patients whose corpus callosum and other tissues which connect the two hemispheres was cut in a procedure called commissurotomy to reduce epileptic seizures. This allowed Sperry to see which hemisphere is specialised to a certain function and whether the hemispheres performed tasks independantly.

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Sperry's Split-Brain Study


An image or word would be projected to a patient's right visual field (processed by left hemisphere) and at the same time a different image could be projected to the left visual field (processed by right hemisphere). In a normal person, the corpus callosum would share the information but in these patients that could not happen.

Key Findings
Describing what you see: When shown to the right visual field, patients could easily describe what they saw but not when shown to the left. ie: language = left hemisphere
Recogniton by touch:
Although patients couldnt attatch verbal labels to objects on the left visual field they could identify it in a bag with their left hand ie: tough = right hemisphere
Compostie words: If two words were presented simultaneously on both fields, they would write the word on the left side but say the word on the right ie: language = left hemisphere and recognition = right hemisphere
Matching Faces:
 When asked to match a face to a series of other faces, picture on left field was consistantly selected ie: recognition = right hemisphere

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Evaluation of Sperry's Study

Demonstrated lateralised brain functions
Sperry's pioneering research into the split brain phenomenon has produced an impressive and sizeable body of research findings, the main conclusion being that the left hemisphere is geared towards analytical and verbal tasks whilst the right is more adapt to performing spacial tasks and music

Strengths of methodology
Sperry was able to ensure that only one hemisphere was recieving information at a time, thus he developed a very useful and well-controlled procedure.

Theoretical basis
Sperry's work prompted a theoretical and philosophical debate about the degree of communication between the two hemispheres in everyday functioning and the nature of conciousness. Some theorists suggest that the two hemispheres are so functionally different that they represent having two minds in the brain.

Issues with generalisation
Unique patients with epilepsy so it is argued that their brains have altered from the norm thus influencing findings

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Ways of Investigating the Brain

works by detecting changes in blood oxygenation and flow that occur as a result of neural activity in specific parts of the brain. When the brain is more active it consumes more oxygen and to meet this increased demand blood flow is directed to the active area. fMRI produces 3D images to show which areas of the brain are involved in certain functions.
Measures electrical activity in the brain via electrodes fixed to an individuals skull using a cap. The scan recording represents brainwave patterns that are generated from the action of millions of neurons, providing an overall account of brainwave activity. These scans may indicate abnormalities such as epilepsy, brain tumours and sleep disorders.
Using a statistical averaging technique, all extrenuous brain activity from the original EEG is filtered out, leaving only the responses that relate to say, the presentation of a specific stimulus.
Post-Mortem Examinations
Involves the analysis of a person's brain after their death. Individuals brains subjected to post mortem are likely to have a rare disorder and have experienced unusual mental processes in their life. Areas of damaged brain are examined, determining cause of affliction.

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Brain Investigation Evaluation

STRENGTH: does not rely on the use of radiation, therefore if administered correctly it is virtually risk free, non invasive and straight forward. WEAKNESS: fMRI can only measure blood flow in the brain, it cannot home in on individual activity of neurons so it is difficult to tell what type of brain activity is being observed
STRENGTH: has proved invaluable in the diagnosis of conditions such as epilepsy, a disorder characterised by random bursts of activity in the brain that can be easily detected on the screen. WEAKNESS: EEG does not allow researchers to distinguish between activities originataing in different but adjacent locations.
STRENGTH: brings much more specific measurements of neural processes that could never be achieved using raw EEG data. WEAKNESS: in order to establish pure data, background noise and extraneous variables must be completely eliminated which is hard to achieve
STRENTH: vital in providing a foundation for early understanding of key processes in the brain, improving medical knowledge. WEAKNESS: Observed damage may not be linked to deficits under review but other trauma or decay.

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Circadian Rhythms

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Circadian Rhythms

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