Plasticity / studying the brain

Plasticity / studying the brain

1. Plasticity

   • Plasticity: The brains ability to change and adapt, functionally and physically, as a result of learning and experience.
   • Information is transferred from neuron to neuron via synapses on it's way through the brain. When we're presented with new information, new neural pathways begin to form. Continuous use of a new neural pathway strengthens it and a neural pathway not in use becomes weaker until it is lost (synaptic pruning).
     • During infancy, the brain has a rapid growth in the number of synaptic conections as we learn and have to adapt more at this stage of our lives, however, it now widely accepted that plasticity occurs throughout adult life as well.
   • Elbert et al - Participants consisted of 9 musicians (either violin, cello or guitar) and 6 non-musicians. A technique called magnetic source imagery was used to measure the area of the somatosensory cortex representing the digits of their left hand of each participant. They found the area representing the digits of the left hand was larger in the musicians than the control group. This suggests that the increased amount of sensory processing required from the left hand of string-playing musicians results in structural changes in the brain to accommodate this. Provides support for plasticity.
     • Weakness - Its been criticised that the increased representation of the left hand may have been a genetic trait rather than as a result of playing an instrument. Therefore, they may have been good musicians naturally so continued to pursue it.

2. Functional recovery

   • A form of plasticity. Following damage from trauma, this is the brain's ability to redistribute or transfer functions usually performed by damaged areas to non-damaged areas.
   • When brain damage occurs (head injury, stroke, tumour, infection etc.) the brain is able to recover some lost function. It does this by rewiring 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'.
     • This is supported by a number of structural changes in the brain including axon sprouting which is the growth of new nerve endings that connect with other undamaged nerve cells to form new neural pathways.
   • Functional recovery tends to reduce with age. In childhood the brain has a greater tendency for reorganisation (as it's constantly adapting to new experiences and learning anyway)
     • Bezzola - Demonstrated how 40 hrs of golf training produced changes in the neural representations of movement in participants aged 40 - 60. Using fMRI researchers observed reduced motor cortex activity in the notice golfers (younger) compared to a control group. This suggests more efficient neural representations were developed after training. Provides support that plasticity occurs throughout someones life.

3. Methods of studying the brain

   • fMRI
     • Detects changes in the blood oxygenation and flow as a result of brain activity in specific areas of the brain. An active area of the brain consumes more oxygen so blood flow is directed there, the differences in the amount of energy released by haemaglobin is detected by a scanner and the change measured.
     • Produces a 3D image that is moving showing which parts of the brain are active when the patient is carrying out a particular mental process. It shows brain activity about 1 second after it occurs.
     • Doesnt rely on the use of radiation - virtually risk free, non-invasive and straight forward to use.
     • Provides structural and functional information. Used for researching the brain (localisation of function), can diagnose medical problems as they can show disease/damaged areas of a brain and are used to study abnormal behaviour.
     • Provides a moving image of brain activity - patterns are clear and can be compared, also accurate for up to 1-2mm in the brain.
     • Expensive to buy/maintain - research is expensive and difficult to organise.
     • Can only measure blood flow in the brain - cannot home into specific neurons therefore it's difficult to determine what brain activity is shown on screen.
   • EEG
     • A skull cap of electrodes (from 2 to over 100) is placed on the individual's head with each electrode measuring the electrical activity that's occurring in the brain directing beneath it.
     • The recording represents brainwave patterns that are generated from the actions of neurons, providing an account of brain activity.
     • It is used as a diagnostic tool, with unusual patterns of brain activity possibly highlighting neurological disorders ie. epilepsy, anorexia nervosa. It is also used in sleep studies and to research disorders such as depression and schizophrenia.
     • EEG has successfully diagnosed conditions - such as epilepsy (disorder characterised by random bursts of energy that can be easily detected on screen)
     • Contributed to the understanding of the stages involved in sleep - the ultradian rhythm
     • Needs expertise to understand - output from the equipment needs to be interpreted and requires training to do so.
     • It generalises the information received from millions of neurons - doesn't pinpoint exact neural activity.
   • ERPs
     • These are the specific stimulus (isolated neural responses) or the performance of a specific task ie. the types of brain waves that were triggered by particular events. These are extracted from the EEG's raw data using statistical averaging techniques that filters out the extraneous brain activity from the original scan.
     • It is used a lot in memory research in gain understanding of information processing and has been used to show differences in mental disorders ie. phobias.
     • Researchers have been able to identify may types of ERPs and describe the precise rile of these in cognitive functioning - eg. the P300 component is thought to be involved in the allocation of attentional resources and maintenance of working memory.
     • Give more of a specific measurement - extracts specific neural processes rather than looking at brain activity as a whole (EEG)
     • Not easy to achieve - the raw EEG data needs to be manipulated in order to filter out extraneous brain activity.
     • Lack of standardisation - different researchers use different ERP methodology therefore it's difficult to confirm findings
   • Post-Mortem
     • Involves the analysis of a person's brain who is dead who in life were likely to have had a rare disorder or unusual deficits in mental processes. Areas of damaged are pinpointed in order to establish a likely cause. A comparison of a 'normal' neurological brain is sometimes carried out to see the extent of any differences.
     • Is used to support localisation of the brain ie. Paul Broca - carried out post-mortems on patients who had speech problems, found both had the same damaged area, now known as Broca's area which is involved in speech production.Also it's been used to establish causation of conditions.
     • Provided foundation for early understanding - Broca and Wernicke relied on post-mortems studies to establish links between brain structure, language and behaviour.
     • Improves medical knowledge - helped generate hypothesises for further study
     • Ethical issues of consent - patients may not be able to provide fully informed consent ie. case of HM who lost his abilities to form memories so couldn't consent but post-mortem still was carried out.
     • Doesn't allow cause and effect to occur - can only see structural differences but not how the brain acts with certain stimuli.