Plasticity, Functional Recoverey and Ways of Studying the Brain

What are the ways of studying the Brain

• fMRI (functional magnetic resonance imaging)

• EEGs (electroencephalogram)

• ERPs (event-related potentials)

• post-mortem examinations

What does a fMRI (functional magnetic resonance imaging) do

• measures oxygenated blood flow in brain (brain activity)

• active areas can be compared with areas lower in activity

• indicated on fMRI scan image via degree of bright colour

How does a fMRI (functional magnetic resonance imaging) work

• oxygenated blood has different resonance

• more active areas of brain receive more oxygenated blood

• fMRI use magnets to detect oxygenated haemoglobin blood flow

• mapped using voxels (thousands of neurons)

Scientific strength of fMRI’s

• fMRI has good spatial resolution of 1mm

• enables researcher to precisely identify (below)

• active brain region and patterns of activation over time

• lead to increased insight on how brain works

• e.g. dopamine in addiction

Ethical strength of fMRI’s

• non-invasive procedure

• participants are protected from injection of potentially harmful substances

• PET involves radioactive tracer

• fMRI has good ethical validity

Delay criticism of fMRI’s

• fMRI is slow (5 second delay)

• between brain activity and measurement

• important information could be not detected due to delay

• fMRI cannot prove a theory

• only indicate biological correlates to behaviour

External Validity criticism of fMRI’s

• fMRI is expensive

• technical specialist equipment and skilled personnel

• use is limited to countries/regions/institutions that afford purchase and maintenance

• economic considerations mean sample sizes in fMRI are small

• limits external validity and reliability of data

What does an EEGs (electroencephalogram) do

• show brain activity

• via brain waves

• presents as series of lines

• has distinct pattern

How do EEGs (electroencephalogram) work

• EEG involves placing electrodes on scalp

• to record brain activity

• 22-34 electrodes used but can be from 2-100

• depends on age, size of participant and aim of research

• electrodes fitted to cap placed on scalp with conductive gel

• electrode measure activity of cells directly below

• more electrodes = more detailed info

What does Amplitude show

brain intensity

What does Frequency show

speed of activation

What is an EEG used to investigate

• sleep disorders

• seizures

• memory problems

Useful strength of EEG

• historically important understanding sleep patterns

• e.g. used to determine 5 different sleep stages

• key find was eye movement linked to dreaming phases

• REM = rapid eye movement

• REM reflected type of dream

• only possible due to EEG

Standardised strength of EEG

• systematic timetable for waking participants

• and collecting dream reports

• objective measure like EEG makes study replicable

• consistency of results can be checked over time

• increased reliability

Limited criticism of EEG

• only detects surface activity in brain

• cannot provide insight to deeper regions of brain

• e.g. amygdala

• EEG limited to what it can achieve (in measuring brain activity)

Issues with Attaching Cap criticism of EEG

• electrode may be placed inaccurately or move during

• each head is unique in shape and size

• hasn’t got a ‘one size fits all’ basis

• some electrodes may not work or need replacing

• leads to unrepresentative findings

What does a ERPs(event-related potentials) do

• records when there is activity in response to stimulus

• can be stimulated by sensory, cognitive or motor events

• ERPs are tiny voltages generated in brains structures

• in response to specific events or stimuli

How does an ERPs(event-related potentials) work

• uses same apparatus and technique as EEG

• original EEG recording used

• white noise is filtered out to leave only what investigating

• using statistical averaging technique

• waveform peaks and dips when specific cognitive process happens

• e.g. language

Cost strength of ERPs

• cheaper than fMRI

• more utilised more readily and widely

• conditions like epilepsy easier to diagnose

Accuracy strength of ERPs

• ERP records brain activity in real time

• measurements every millisecond of brain activity

• results in accurate measurement

• of electrical activity when specific task performed

Comfort criticism of ERPs

• electrode cap participants find uncomfortable

• leads to subject attrition

• therefore lower sample size and robust data

• participants may wriggle, scratch or pull

• altering validity of findings

Precision criticism of ERP

• ERP signal cannot pinpoint with 100% accuracy

• exact source of specific brain activity

• more than one electrode may pick up activity’s signal

• lead to confusion what signal is and from which part brain originates

What does a Post-Mortem Examination do

• determine the cause of behaviour or dysfunction

• experienced when patient was alive

• investigate structure of brain

• cannot detect brain activity

How do Post-Mortem Examinations work

• examine the brain after death

• usually cut into slices

• findings used to infer a correlation with behaviour

• may involve comparing damaged brain to non-damaged brain

• to assess which region are implicated in behaviour observed when alive

Why were Post-Mortem Examinations used

• early days of biopsychology

• no sophisticated tech available to look at brain

When are Post-Mortem Examinations used today

• if no alternatives available

• alzheimer’s disease can only be determined by PME

How was Post-Mortem Examination used for HM

• alongside other techniques to investigate damage in HM

• helped determine link between hippocampus and formation of new memories

• after HM died his preserved brain sent to Uni of Cal

• sliced into 2401 sections and scanned on slides

• as permanent neurological research resource

How was Post-Mortem Examination used for Tan

• Broca’s patient was scientific breakthrough

• in locating language area of brain in left hemisphere

• Tan only could say tan

• but understood conversation

Harm Free strength of PME

• enables research to study brain without inflicting harm on person

• as long as consent is given

• ethical way to investigate brain structure/abnormality

Conformation strength of PME

• patient suspected of alzheimer’s

• PET scans conducted indicating it present

• but scan itself could not diagnose with 100% confidence

• PME determines conclusively that patient suffers from alzheimer

Ecological criticism of PME

• difficult to compare post-mortem slices of brain

• with actual brain functioning before death

• lacks ecological validity as the ‘real’ living brain of person is not reflected

Consent criticism of PME

• may not always be possible for researchers to obtain fully informed consent

• from prospective PME participant

• particularly true if ability to consent is severely compromised by disorder

• e.g. HM has amnesia so consent by proxy only

• limits ethics of PME

What is Neuroplasticity

• brain’s ability to adapt to change

• due to injury, damage from illness

• or change due to learning and experience

What is Structural Plasticity

• changes within brain structures

• e.g. increased grey matter built up in posterior hippocampus

• due to learning experienced over time

• not immediate, developed slowly

• in response to either degree of damage or extent of learning experience

What is the buildup of grey matter due to

increased synaptic connectedness in brain regions involved

What does Plasticity mean

• brain is not static concrete mass

• brain is flexible organ

• responds and adapts to environmental stressors

Examples of Neuroplasticity

• london black cap taxi drivers years long learning routes through central

• brains adapt by increasing grey matter

• juggling routine learnt increased grey matter

• once juggling ceased for 3 months the grey matter linked to juggling decreased

• jugglers brain showed evidence of neural pruning

• mindfulness practised increased grey matter in prefrontal cortex

• mindfulness practised decreased grey matter in amygdala

What is Functional Plasticity

• brain’s ability to replace lost or damaged functions

• using existing brain regions

• e.g. mobility, memory and language taken over by healthy brain regions

• capable of replacing lost functionality stand in but not 100%

What is an example of Functional Plasticity

• child had half of brain removed

• (hemispherectomy)

• to control epilepsy

• can now function almost normally after surgery

• remaining hemisphere takes over the tasks of removed hemisphere

What are the Key Structural Changes

• axonal sprouting

• reformation of blood vessels

• recruitment of homologous areas

• neural pruning

What is Axonal Sprouting

• new growth of nerve endings

• from surviving neurons

• fibres link up with other undamaged cells

• to form alternative neural circuits

What is Reformation of Blood Vessels

• damaged tissue stimulates angiogenesis

• restoring oxygen and nutrient supply

• to recovering areas

What is Recruitment of Homologous Areas

• regions in opposite hemisphere adopt functions of injured zones

• e.g. broca area damaged so right hemisphere equivalent compensate over time

What is Neural Pruning

• use-dependent refinement - synapses used frequently grow stronger

• unused ones are cleared out

• pruning makes network leaner and more efficient

• structurally and functionally

• Draganski’s study - learning-induced growth

• followed by selective pruning of excess connections

Case Study of Functional Plasticity/Recovery

• danelli et al conducted a case study of EB

• 14yo boy with brain damage

• at 2 EB had hemispherectomy on left side to remove tumour

• language centres removed (incl. Broca and Wernicke)

• immediately after EB lost all language functions

• after 2 years EB recovered his language ability even without left side

• fMRI scans showed right side was acting as if it was the left

• in terms of language functions

What does the case of EB demonstrate

• functional recovery

• brain can adapt and recover after trauma

Why does Functional Recovery have a Time Stamp

• recovery early in life has chance of full recovery

• older people less likely

• brain ageing and decrease in synaptic activity

How should Rehabilitative Therapy be altered for Functional Recovery

• begins with rapid growth spurt

• slows down

• eventual plateau after some time

• reflected in therapy

Research Support strength of Plasticity & Functional Recovery

• impressive body of research into neuroplasticity

• findings supporting idea that brain adapts to change

• good internal validity (different studies same conclusion)

• researchers can exclude other explanations for findings

Practical strength of Plasticity & Functional Recovery

• understand brain’s capacity to compensate for loss

• being aware of slowing-down phase

• key to informing therapy (physical and cognitive)

• for patients with brain damage

Not Universal criticism of Neuroplasticity

• not always happened when needed

• HM removed hippocampus at 27

• anterograde amnesia

• never recovered any functionality

• short-term memory affected permanently

• does not apply in every case, casting doubt

Correlational criticism of Plasticity & Functional Recovery

• research in field is correlational only

• cause-effect cannot be established

• leaves too many unanswered questions

• e.g. why does grey matter build up in specific brain regions

• e.g. what other factors could account for grey matter

• sample sizes used are generally small