Baba neuroplasticity

What is neuroplasticity?

Neuroplasticity refers to the brain's ability to adapt and change in response to experience, learning, or damage. The brain is not a static, concrete mass. It is a flexible organ that responds and adapts to environmental stimuli and stressors.

There are two key processes:

· Plasticity: Changes in the brain's structure and connections due to learning and experience

· Functional recovery: The brain's ability to reorganise itself and recover lost functions after trauma or injury

What is plasticity and what is neural pruning?

Plasticity refers to changes within brain structures and connections in response to learning, experience, or repeated activity. These changes happen gradually and reflect the degree of learning or experience. The build-up of grey matter in particular brain regions is due to increased synaptic connections in those areas.

Plasticity also involves neural (synaptic) pruning, where frequently used synapses are strengthened and unused ones are cleared away, making the network more efficient.

What are examples of neuroplasticity?

London black cab taxi drivers spend years learning routes through central London. Their brains show increased grey matter in the posterior hippocampus, a region linked to spatial navigation (Maguire et al. 2000)

· People who learn a juggling routine show increased grey matter in the mid-temporal cortex compared to non-jugglers. When the jugglers stopped practising for three months, the grey matter linked to juggling decreased (Draganski et al. 2004). This shows both plasticity (growth) and neural pruning (loss of unused connections)

· People who practice mindfulness show increased grey matter in the prefrontal cortex and decreased grey matter in the amygdala. Participants reported a decrease in stress and anxiety symptoms (Gotink et al. 2016)

What is functional recovery after trauma?

Functional recovery refers to the brain's ability to recover lost functions after trauma or injury. It does this by reorganising itself and using healthy regions to take over the work of damaged ones. Functions such as mobility, memory and language can be partially or fully recovered, although recovery is not always 100% of the original ability.

Functional recovery tends to begin with a rapid growth spurt, then slow down and eventually plateau. Recovery is generally faster and more complete in younger brains, as ageing brains have reduced synaptic activity.

What are the mechanisms of functional recovery?

Axonal sprouting: New nerve endings grow from surviving neurons and link up with undamaged cells, forming alternative neural circuits

· Reformation of blood vessels (angiogenesis): Damaged tissue triggers the growth of new blood vessels, restoring oxygen and nutrients to the recovering area

· Recruitment of homologous areas: The equivalent region in the opposite hemisphere takes over the function of the damaged area (e.g. if Broca's area in the left hemisphere is damaged, its right-hemisphere counterpart may compensate over time)

· Neural reorganisation: Surviving regions adapt their function and form new connections to support the lost ability

What are examples of functional recovery?

A child who had half of her brain removed (hemispherectomy) to control her epilepsy was able to function almost completely normally after surgery. This was because her remaining hemisphere took over the tasks of the removed hemisphere

· Danelli et al. (2013) conducted a case study of E.B., a 14-year-old boy who had undergone a left hemispherectomy at age 2 to remove a tumour. The surgery removed his language centres, including Broca's and Wernicke's areas. Immediately after surgery, E.B. lost all language function. Two years later, E.B. had recovered his language ability. fMRI scans showed that the right hemisphere was carrying out language functions normally performed by the left. This demonstrates functional recovery and the brain's ability to adapt after trauma

What are the strengths of plasticity and functional recovery research?

There is a strong body of research into neuroplasticity supporting the idea that the brain adapts to change. When several different studies come to the same conclusion then the theory has good internal validity - this means that researchers can rule out alternative explanations.

There are significant practical applications for both plasticity and functional recovery. Understanding the brain's capacity to compensate for loss and the slowing-down phase of functional recovery is key to informing physical and cognitive rehabilitation for patients with brain damage.

What are the limitations of plasticity and functional recovery research?

Neuroplasticity and functional recovery do not always occur when needed e.g. The case of H.M. who had his hippocampus removed at the age of 27 and went on to suffer catastrophic anterograde amnesia. He never recovered short-term memory function. This casts doubt as to the universality of plasticity and functional recovery, as they do not apply in every case.

Much of the research in this field is correlational. This means that cause and effect cannot be established. It leaves too many unanswered questions e.g. why does grey matter build up in specific brain regions, and what other factors might account for the changes?

Sample sizes in this research are often small (e.g. Maguire used only 16 taxi driver participants). This limits how confidently findings can be generalised.

What is fMRI and what does it measure?

Functional Magnetic Resonance Imaging (fMRI) measures oxygenated blood flow in the brain i.e. brain activity. Oxygenated blood has a different resonance than deoxygenated blood. More active areas of the brain receive more oxygenated blood.

fMRI uses large magnets to detect oxygenated haemoglobin blood flow. The blood flow reacts to the scanner's magnets. Deoxygenated blood is present in less active/non-active regions of the brain. The blood flow equates to activity in the brain which in turn indicates which specific structures are working hard at that point in time.

A computer transforms the information into a brightly coloured 3D image which is mapped using voxels (each voxel = thousands of neurons). The active areas of the brain can then be compared with areas that are lower in activity which is indicated on the fMRI scan image via the degree of bright colour.

What are the strengths of fMRI?

fMRI scans have good spatial resolution of 1mm. This is a strength as it enables researchers to precisely identify the active brain regions and patterns of activation over time. This in turn can lead to increased insight into how the brain works e.g. the role of dopamine in addiction.

It is a non-invasive procedure which means that participants are protected from injections of potentially harmful substances (PET scans involve injection of a radioactive tracer into the participant). This means that fMRI has good ethical validity.

What are the limitations of fMRI?

fMRI is slow, having a 5-second delay between brain activity and measurement. This is a limitation as it could mean that some important information is not detected due to the delay. Therefore fMRI scans cannot 'prove' a theory, they can only indicate biological correlates to behaviour (e.g. lack of pre-frontal cortex activity and low impulse control).

fMRI scans are expensive due to the highly technical, specialist equipment and highly skilled personnel involved. This means that its use is limited to countries, regions or institutions that can afford to purchase and maintain the scanners. Economic considerations also mean that sample sizes in fMRI research tend to be small, which limits both the external validity and reliability of data.

What is an EEG and what does it measure?

The use of an electroencephalogram (EEG) involves the placing of electrodes on the scalp which record brain activity. Usually between 22-34 electrodes are used but there can be any number from 2-100 depending on the age and size of the participant and what the aim of the research is.

The electrodes are fitted to a cap that is placed on the participant's scalp along with a conductive gel. The electrodes measure the activity of the cells directly below them. The more electrodes there are, the more detailed information and a comprehensive picture of the brain can be derived.

Brain activity is shown via brain waves. This presents visually as a series of lines which have distinct patterns. The amplitude shows the brain intensity and the frequency shows the speed of activation - this indicates the nature of the brain activity (e.g. if the brain is in 'resting' mode, if it is highly active etc.). EEGs may be used to investigate sleep disorders, seizures, memory problems.

What are the strengths of EEGs?

EEG has been historically important in understanding sleep patterns e.g. Dement & Kleitman (1957) used EEG to determine the five different stages of sleep. A key finding was that eye movements were linked to phases of dreaming (this was termed REM = rapid eye movement). Eye movements reflected the type of dream e.g. a dream about throwing tomatoes at a wall occurred when the participant's eyes moved side to side. These findings were only possible due to the use of EEG.

The use of EEG in the study described above contributes to the overall reliability of the technique. The researchers used a systematic timetable for waking participants and collecting dream reports. This standardized procedure and use of an objective measure such as EEG makes the study replicable. Replicability is a strength as it means that consistency of results over time can be checked = reliability.

What are the limitations of EEGs?

EEG can only detect surface activity within accessible regions of the brain. This is a limitation as EEGs cannot provide insight as to what is happening in deeper regions of the brain (e.g. the amygdala). Therefore EEG is limited as to what it can achieve in terms of measuring brain activity.

Attaching electrodes to the scalp is beset with problems. The electrodes may be placed inaccurately or may move during the procedure. Each person's head shape and size is unique so the placement of the electrodes cannot be done on a 'one size fits all' basis. Some of the electrodes may not work during the procedure or need replacing. All of the above can lead to unrepresentative findings.

What are ERPs and what do they measure?

Event-related potentials (ERP) use the same apparatus and technique as EEG. ERPs record when there is activity in response to a stimulus. ERPs are tiny voltages generated in brain structures in response to specific events or stimuli. ERPs can be stimulated via a wide variety of sensory, cognitive or motor events.

An original EEG recording is used. The 'white noise' of the recording is filtered out to leave only what the researcher is interested in investigating. This is done using a statistical averaging technique. The EEG's waveform peaks and dips show exactly when a specific cognitive process happens in the brain in relation to when the stimulus is presented e.g. language, attention.

What are the strengths and limitations of ERPs?

Strengths:

· ERPs are much cheaper than the more costly fMRI scanning. This is a strength as it means that they are likely to be utilised much more readily and widely than other more expensive techniques. Therefore conditions such as epilepsy may be easier to diagnose

· ERPs record the brain's activity in 'real-time'. They take measurements of brain activity every millisecond. This is extremely useful as it results in an accurate measurement of electrical activity when a participant performs a specific task

Limitations:

· Participants may find wearing the electrode cap very uncomfortable. This is a limitation as it could lead to subject attrition which would in turn mean a lower sample size and less robust data. Additionally, if the cap is uncomfortable participants may wriggle, scratch or pull at the cap which could alter the validity of the findings

· An ERP signal cannot pinpoint with 100% accuracy the exact source of specific brain activity. More than one electrode may pick up the activity's signal. This can lead to confusion as to what the signal is and from which part of the brain it originates

What are post-mortem examinations?

Post-mortem examination (PME) of the brain involves examining the brain after death (usually when it has been cut into slices) to determine the cause of behaviour(s) or dysfunction experienced when the patient was alive. This technique was used in the early days of biological psychology as there was no sophisticated technology available to look at a living brain.

PME is used to investigate the structure of the brain - it cannot detect brain activity. The findings are used to infer a correlation with behaviour e.g. why can patient X not recall any new information? Why is patient Y unable to speak in full sentences?

PME is used today if there are no alternatives available e.g. Alzheimer's disease can only really be determined by conducting a PME.

PME of the brain was used alongside other techniques to investigate the damage done to HM's brain and helped to determine the link between the hippocampus and the formation of new memories. A year after HM died, his preserved brain was sent to the University of California where it was sliced into 2,401 sections. These slices were then placed on slides and scanned, as a permanent neurological research resource.

Paul Broca's (1861) PME of his patient 'Tan' provided a scientific breakthrough in terms of locating the language area of the brain in the left hemisphere. PME may involve comparing the damaged brain to a non-damaged brain in order to assess which regions/structures are implicated in the behaviours observed when the patient was alive.

What are the strengths and limitations of post-mortem examinations

Strengths:

· PME enables researchers to study a brain without inflicting any harm on the living person. As long as the participant has given consent for this to take place this is an ethical way in which to investigate brain structure/abnormality

· PME can help clinicians to confirm a diagnosis e.g. the patient was suspected of having Alzheimer's. PET scans were conducted which indicated that Alzheimer's was present but the scan itself could not diagnose this with 100% confidence. The PME determined conclusively that the patient suffered from Alzheimer's

Limitations:

· It is difficult to compare post-mortem slices of a brain after death with actual brain functioning before death. This means that PME lacks ecological validity as the 'real', living brain of the person when alive is not reflected in the use of this technique

· It may not always be possible for researchers to obtain fully informed consent from a prospective PME participant. This is particularly true if the person's ability to give consent is severely compromised by their disorder e.g. HM's extreme amnesia meant that consent by proxy only was possible. This limits the ethics of PME to some extent