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Localisation of Function in the Brain

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Localisation of Function in the Brain

Localisation of function in the brain is the concept that some brain regions are responsible for particular functions. They carry out and oversee the functions of behaviours and processes due to their structure and position. Examples include moving a limb or being able to speak.

This idea contrasts with the holistic view of the brain, which says that the brain's functions spread across large areas, if not the entire brain itself.

Therefore, when a particular brain area is damaged, this affects that area's associated function.

The brain has a left and right half called hemispheres which operate contralaterally.

Contralaterally refers to the side of the body opposite to which a function is responsible. So, the right hemisphere is responsible for the left side of the body and vice versa.

The corpus callosum connects the hemispheres.

Each hemisphere specialises in performing certain functions, which is called hemispheric lateralisation.

The cerebral cortex is critical. It is a thin outer layer of neural tissue, usually 2-4mm thick, of the brain. It is folded for the extra space (the bumps and ridges are known as the gyri, and the sulci are the furrows) and contains mainly cell bodies. Often referred to as grey matter, higher cognitive processes occur there, such as consciousness, reasoning, emotions, and language, amongst other things.

What are the examples of localisation of function in the brain?

Particular areas are well-known for their relation to specific functions in the brain. Evidence for localisation of function can be seen in multiple aspects of the brain.

The prefrontal cortex

The prefrontal cortex is part of complex cognitive processes and higher-level functions. It is involved in executive functions (sorting through complicated and conflicting thoughts etc.) and working memory, orchestrating thoughts and personality expression and performing cognitive functions whilst inhibiting impulsive thoughts and actions.It is said to be directly involved with consciousness and sentience, so it is incredibly influential on cognitive functions and processes as a whole!

The motor and somatosensory cortex

The motor and somatosensory cortex are areas of the cerebral cortex that run along a fold in the brain called the central sulcus. The motor cortex, responsible for muscle control, is located at the back of the frontal lobe, and the somatosensory cortex, responsible for processing sensations, is located in the parietal lobe.

The functions are carried out contralaterally. If you were to move your left hand, neurones in the right motor cortex would activate. Similarly, if you feel something tickle your left hand, the right sensory cortex would activate.

Localisation of Function in the Brain Brain areas StudySmarter

Brain areas labelled with motor and somatosensory areas, Wikimedia Commons

The motor cortex is responsible for:

  • Planning and carrying out voluntary movement, such as choosing to move a limb. Precisely, the nonprimary motor is involved with sequencing movements, where you go through the process of planning and carrying out a task, e.g., getting dressed.
  • Coordinating the two sides of the body through movements.
  • Spatial and sensory guidance of movement lets you navigate through areas with voluntary control of your muscles.

Damage to these areas can result in the loss of the above functions. Paralysis may occur, as there's a loss of voluntary control over muscles. It is difficult to sequence movements or actions. For example, it would be harder to get dressed. Dexterity is affected; when the motor cortex is damaged, the more complex the movements are, the harder it is to carry them out. Eventually, with damage and muscle control loss, the muscles will become weaker, resulting in atrophy (loss) of the muscles.

The somatosensory cortex is situated in the postcentral gyrus (the bumps and ridges that make up the cerebral cortex), found in the parietal lobe, as seen in the above diagram.

Localisation of Function in the Brain Primary somatosensory cortex StudySmarter

Primary somatosensory cortex, dbcls.rois.ac.jp

The somatosensory cortex is contralaterally responsible for:

  • Receiving and processing sensations, such as touch and temperature.

Damage to the somatosensory cortex causes a loss of sensation from the opposite side of the body. It can result in one area being completely ignored, or there may be a loss of ability to recognise an object by its feel, known as agnosia.

The visual cortex

The visual cortex is located in the occipital lobe at the back of the brain.

Light enters the eye and is converted into nerve impulses by the retina (located at the back of the eye). The optic nerve transmits these impulses to the thalamus and the visual cortex.

The right hemisphere processes visual information of the left eye, and vice versa for the left hemisphere. It operates contralaterally.

It is responsible for:

  • Visual processing functions – it receives visual information and integrates it with various other functions, processing the data and sending it to be utilised elsewhere (such as by the motor cortex to navigate the body to pick something you have seen). Therefore, the brain can recognise things in the environment more efficiently.

Damage to the visual cortex can result in partial or complete contralateral blindness, known as cortical blindness.

Localisation of Function in the Brain Human visual pathway StudySmarter

Human visual pathway, Miquel Perello Nieto, Wikimedia Commons

The auditory cortex

The auditory cortex is located at the top of the temporal lobe. The primary auditory cortex receives auditory information from the thalamus, which receives sound impulses (sensations) from the cochlea.

The cochlea converts sound waves into nerve impulses, carried by the auditory nerve for the auditory cortex to process and interpret.

The auditory cortex is responsible for:

  • Perceiving sound includes pitch, tone, frequency, and what type of sound it is.
  • Determining where the origin of the sound.
  • Determining what produced the sound.

Damage to this area can cause issues such as being unable to detect changes in a person's pitch or tone of voice, making conversing with someone and interpreting their intentions extremely difficult. If someone is serious or sarcastic, it would be hard to tell by pitch or tone alone. They wouldn't be able to determine where or what produced the sound.

Broca's area

Broca's area is located in the left frontal lobe, as illustrated below:

Localisation of Function in the Brain Broca's Area StudySmarter

Broca's area, dbcls.rois.ac.jp

The exact location of Broca's area is up for debate, but researchers agree that it is located in the left frontal lobe.

It is responsible for:

  • Speech production, featuring heavily in language.
  • Breathing during vocalisation.

Broca's area is in the left hemisphere specifically. The right hemisphere has a similar area, but it's not as pertinent.

Broca discovered the area when a patient with a severe leg infection came to him and could only produce the word 'tan'. The patient struggled immensely with speech production. The patient wanted to communicate but just couldn't. The only words Broca heard him say were 'God damn' in French due to his frustration over not speaking.

After the patient died, Broca performed an autopsy and found a large crater in the left frontal lobe. Broca ascribed this lesion (damage) to the loss of speech production in the patient. He discovered eight more cases with similar evidence and speech production issues to confirm this. It was the same place and on the left side.

The original patient became the first to be described as suffering from Broca's aphasia (a loss of ability to produce speech due to brain damage).

Therefore, the function of speech production was localised to Broca's area.

Wernicke's areas

Wernicke's area is primarily said to be located in the upper temporal lobe, shown below:

Localisation of Function in the Brain Wernicke's area StudySmarter

Wernicke's area, dbcls.rois.ac.jp

It resides in the left hemisphere. The left hemisphere is becoming increasingly prominent in its dominance of language production functions.

Wernicke suggested damage in the left hemisphere, specifically the area we're discussing, would result in fluent but meaningless speech.

Patients could speak with fluent sounds and inflexions (changes in pitch to give meaning), but when listened to, the sound made little sense. This disorder is known as Wernicke's Aphasia. People often also struggle to understand language with this disorder.

Wernicke proposed a model including his and Broca's area to state that Wernicke's area is responsible for meaningful speech, and Broca's area is responsible for making plans and generating speech (through moving the mouth and tongue).

Damage to Wernicke's area does not always wholly disrupt comprehension, suggesting it is just one component of language comprehension.

Damaging Broca's and Wernicke's areas can result in global aphasia, where patients struggle to produce and understand speech.

Localisation of Function in the Brain Human brain areas StudySmarter

Human brain areas: Orange = Angular Gyrus, Yellow = Supramarginal Gyrus, Blue = Broca's Area, Green = Wernicke's Area, Pink = Primary Auditory Cortex, Reid Offringa and Selket, Wikimedia Commons

Evaluation of localisation of function in the brain

There are strengths and weaknesses for the argument of localisation of function within the brain.

Strengths

  • Confirmation by loss of function: Broca's and Wernicke's Areas are direct examples of where damage to a specific, localised area can cause a loss of function and ability. When this occurs, damage in these areas causes speech production and memory issues. Broca's aphasia and Wernicke's aphasia are explicit examples of localised functions the damage affects. The function is thus tied to a specific area, supporting the localisation of function in the brain.
  • Confirmation through neuroimaging techniques: Modern brain scanning techniques show activation in areas of the brain related to specified areas highlighted in older research. In studies on patients performing tasks, such as speaking, Broca's and Wernicke's areas were active in fMRI. These were in healthy patients, too.
  • Double Dissociation: Where dissociation (damage to the brain that affects one function, but not another) occurs in one patient, the opposite can occur in another patient. So, if one person has a damaged Broca's area and their speech production is affected, they are compared to someone with a damaged Wernicke's area, where their speech comprehension is affected.This comparison allows for functional associations to be made, as Broca's area affected patient can understand language, and Wernicke's area patient can produce language. Damage has affected one function but not the other.
  • Transcranial Magnetic Stimulation: Magnetic pulses stimulate the brain (a coil is placed over the head). Barker et al. were able to use TMS to produce recordable responses in the motor cortex.¹ Bolognini and Ro found that a single pulse can disrupt visual perception when we apply TMS to the visual cortex.² A single pulse to the motor cortex can disrupt hand muscle use.

Weaknesses

  • Dronkers et al.³ found that when re-examining the brain of Broca's famous patient, Tan, lesions extended significantly beyond the areas Broca initially highlighted. There were inconsistencies in what is now called Broca's area. How can we confidently say that this specific area is responsible for speech production? These inconsistencies raise significant issues with the validity of this area and the functional associations.
  • The equipotentiality theory suggests that basic functions, such as motor and sensory (moving your arm, speaking, feeling something and tasting something), are localised, but higher cognitive functions are not.
  • Reductionist: Some argue it is important to discuss how these brain areas communicate with each other, rather than focusing on the reductionist argument of localised functions. By stating one area is responsible for complex human behaviours, it detracts from human experiences.
  • Functions aren't completely localised: Déjerine exemplifies how localisation is not as credible as first thought. (4) In this study, a patient suffered damage after having a stroke between the connection of the visual cortex to Wernicke's area. He lost his ability to read as a result, but not his writing ability. The lesions isolated the left angular gyrus, or 'language zone', from the visual cortex. Damage to the connection of the two areas was similar to the damage had it occurred to the localised area, which suggests that functions are not completely localised.
  • Cuomo et al. found a similar result in their study, where a teacher was taking attendance in her class but could not understand any of the words or letters on her sheet. (5) When checking her lesson plan, it was the same.It was discovered she had had a stroke and had alexia without agraphia. It interrupted communication to the language zone. Unfortunately, the teacher could not relearn the ability to read, but by tracing the letter specifically in a word, she could begin to recognise and decipher words this way. It is a much lengthier process but a fascinating reimagination of what it is to read. This incident supports the idea that functions are not tied locally to one specific area. The interruption of communication to the language zone caused the disorder, not particular damage to the language zone.
  • Localisation doesn't acknowledge individual differences. Men and women have different sized brain regions, and Harasty et al. found that women had larger Broca's and Wernicke's areas than men, which could account for their differences and greater use of language. (6) This causes issues with beta bias, where these studies largely ignore sex differences.
  • Plasticity of the brain: functions can be adopted by other brain areas when trauma occurs. If the function is localised, another, unrelated portion of the brain should not take over this function. An example in Danelli et al. shows how the patient, known as EB, had their left hemisphere removed at the age of two due to a tumour. (7) Despite this, they regained full use of their language abilities with only mild language comprehension disorders (dyslexia). The right hemisphere had adapted to deal with the damage.

Localisation of Function in the Brain - Key takeaways

  • Localisation is the concept that certain brain areas are responsible for particular functions. This idea contrasts with the holistic view of the brain, which essentially says that the brain's functions spread across large areas, if not the entire brain itself.

  • Hemispheric lateralisation is where each brain hemisphere is specialised to perform certain functions. The brain generally operates contralateral.

  • The motor cortex is responsible for motor control, and the somatosensory cortex is responsible for sensation processing.

  • The visual cortex is responsible for visual processing functions and perceiving information. Damage to the visual cortex can result in partial or complete contralateral blindness, known as cortical blindness. The auditory cortex is responsible for sensing sound. Damage to this area can cause issues with understanding speech, what sound came from, and what specific sounds mean.

  • Broca's and Wernicke's areas are in the left hemisphere specifically. Broca's area is responsible for speech production, Wernicke's area is responsible for speech comprehension.

  • Both modern and old research supports localisation – fMRI shows activated areas, and damage to these areas disrupts associated functions. TMS can actively disrupt localised functions, and double dissociations support localised functions.

  • Issues arise with equipotentiality theory, beta bias, and how damage can extend beyond localised areas but still affect the functions associated with those areas.

Frequently Asked Questions about Localisation of Function in the Brain

Localisation of function in the brain is important because it helps researchers identify brain areas that could be responsible for specific functions. It aids massively in researching the complexity of the organ.

Functional localisation is the concept that some brain regions are responsible for particular functions.

Localisation is where a specific brain area is associated directly with a particular function. Lateralisation is where the brain has two hemispheres connected by the corpus callosum, and each hemisphere of the brain is specialised to perform certain functions or processes.

Many areas of the brain are associated with memory control. This includes the prefrontal cortex, the amygdala, the hippocampus, and the cerebellum.

Final Localisation of Function in the Brain Quiz

Question

What is the localisation of function in the brain?

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Localisation is the concept that some brain regions are responsible for particular functions. They carry out and oversee the functions of behaviours and processes due to their structure and position.

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How does localisation of function in the brain contrast with the holistic view of the brain? 


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The holistic view of the brain states that functions occur across the entirety of the brain. Localisation suggests that specific functions occur in certain parts of the brain, not the whole of the brain.

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What is hemispheric lateralisation? 


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Hemispheric lateralisation is where each brain hemisphere is specialised to perform certain functions.

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What does contralateral mean? 


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Contralaterally refers to the side of the body opposite to which a function is responsible. So, the right hemisphere is responsible for the left side of the body and vice versa.

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What fold in the brain do the motor and somatosensory cortex run along? 


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The fold in the brain that the motor and somatosensory cortex run along is called the central sulcus. 

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What are the functions of the motor cortex? 


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The functions of the motor cortex are planning and executing voluntary movement, such as choosing to move a limb as well as spatial awareness and coordinating the two sides of the body.

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What happens if the motor cortex is damaged? 


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When the motor cortex is damaged, some muscles will no longer be voluntarily controlled, and in extreme cases, this can lead to total paralysis of certain parts of the body.


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What are the functions of the somatosensory cortex? What happens if it is damaged? 


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The function of the somatosensory cortex is receiving and processing sensations, such as touch and temperature. If the somatosensory cortex is damaged, people may lose sensation on the opposite side of the body.

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What are the functions of the visual cortex? 


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The visual cortex is responsible for processing visual information.

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What happens if the visual cortex is damaged?

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Damage to the visual cortex can result in partial or complete cortical blindness. 


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What are the functions of the auditory cortex? 


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The auditory cortex is responsible for perceiving sound, including pitch, tone, frequency, and determining its type.


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What are the functions of Broca’s area? What are the functions of Wernicke’s area?

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Broca’s area is responsible for speech production. Wernicke’s area is responsible for speech comprehension.

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Where are Broca’s and Wernicke’s areas located?

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Broca’s and Wernicke’s areas are both located in the left hemisphere.

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What is Broca’s aphasia? 


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In Broca’s aphasia, the damage occurs in Broca’s area in the brain, resulting in a loss of ability to form words and sentences.

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What is Wernicke’s aphasia?

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When Wernicke’s area is damaged, people struggle to understand speech. They may speak fluently, but it is meaningless and makes no sense.


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What connects the two hemispheres of the brain?

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The corpus callosum. 


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What is hemispheric lateralisation? 


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Hemispheric lateralisation is the idea that functions are divided up and performed by the different hemispheres of the brain; the hemispheres are specialised in certain functions and are not entirely alike.

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What area of the brain is a good example of a localised function? 


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Broca’s area is localised to the left hemisphere.

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What did patients suffer with before their corpus callosum was severed in Sperry's experiment? 


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Severe epilepsy.

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What three tasks did Sperry have patients do?

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The patients had to describe what they saw, tactile tests, and draw what they saw.

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What happens when the corpus callosum is severed? 


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Information is not shared between the right and left hemispheres.

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If an image was presented to the left visual field, what did patients struggle in doing? 


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Patients were unable to say what they had seen, as the language area of the brain had not been given the information of what the right hemisphere had seen through the left visual field.

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What did Sperry find?

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He found that people with split brains have two, separate visual inner worlds, each with its interpretation of visual images. There’s a lack of communication/cross-integration - one hemisphere does not know what the other is doing. There seem to be two streams of consciousness, each with its own memories, perceptions, and impulses. 

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What did Sperry conclude? 


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The conclusions indicate that the left hemisphere is dominant in speech production and language, whilst the right hemisphere is dominant in visual-motor tasks.

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Name one strength of hemispheric lateralisation? 


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It increases neural capacity, allowing for each hemisphere to specialise and attend to tasks simultaneously.

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Name a weakness of hemispheric lateralisation?

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Lateralisation decreases with age / Research carried out on animals / Split-brain procedures are rarely carried out now / Hard to generalise / Contradicting claims of the right hemisphere 

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What did Rogers et al. (2004) chicken study find? 


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Chickens with lateralisation enhanced their ability to find food and watch out for predators simultaneously. 


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What did Szaflarski et al. (2006) find?

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In fMRI studies on language lateralisation, a dominant hemisphere’s control increases from ages 5 to 20 years, plateaus (flattens out/remains steady) from ages 20 to 25 years, and decreases between 25 and 70 years.

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What did Turk et al. (2002) find?

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In the case of JW, they found that he had developed the ability to speak using the right hemisphere, so he could speak about the information given to both sides of the brain/visual fields. 


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What is plasticity in the brain?

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Plasticity is the brain’s ability to change and adapt to the environment, both in function and structure.

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What is synaptic pruning? 


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Synaptic pruning is when neuronal pathways are weakened or removed altogether due to lack of use/repetition. 


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What does synaptic pruning achieve? 


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It improves the brains communication efficiency, as it removes unnecessary or weakened pathways, but the ones remaining are stronger. 


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What is axonal sprouting? 


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This is when new connections form, with neuronal cell bodies forming additional branches and axons. 


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What did Kolb and Robinson (2004) find in their study?

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They found that addictive substances such as nicotine and morphine cause changes in the structure of dendrites and dendritic spines in brain regions, such as the nucleus accumbens and the prefrontal cortex. 


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What is neural regeneration?

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This is when new neurones and connections generate after an area of the brain is damaged. 


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What are the two types of trauma that can occur to the brain? 

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Direct and indirect. 


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What is denervation supersensitivity?

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When there is a loss of axons in a pathway, possibly from a result of direct or indirect trauma, the remaining axons become more sensitive as a result.

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What did Cannon and Rosenblueth (1949) find in their study? What term did they create? 


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They created the term ‘law of denervation.’ In their study, they found that surgical denervation causes supersensitivity in neurones. The closer the neurones are to the damaged areas/cut neurones, the greater the supersensitivity. This decreases the chain of neurones.

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What is functional reorganisation?

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Where injury has occurred, healthy portions of the brain undergo functional reorganisation to regain the ability to do the function that has been lost. Functions lost are ‘picked up’ by unassociated areas of the brain, to regain function. 


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What is neuronal unmasking? 


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This is where areas close to the damaged portions of the brain that have dormant synapses (synapses that haven’t received enough input to be active), open connections to compensate for the damaged areas. 


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What are the three factors affecting functional recovery? 


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Age, gender, and rehabilitative therapy.

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What did Maquire et al. (2000) find in their study?

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When comparing taxi drivers who had undergone ‘The Knowledge’ test in London to a control group, taxi drivers had significantly larger posterior hippocampus’s, positively correlated with their time spent as taxi drivers. This suggests the physical structure of the brain can change depending on the environment and the experiences of the individual.

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What did Danelli et al. (2013) find in their study? 


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When EB (a 14-year-old) had a tumour removed as an infant, through a left hemispherectomy (removing Broca’s and Wernicke’s areas, language centres of the brain), the child developed normally despite this significant trauma to the brain, with only a few language issues (dyslexia). The right hemisphere adapted to compensate for the missing brain functions. 

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What is the case of Phineas P. Gage?

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A man working on a railway in 1848 received significant brain injury when an iron bar went through his left frontal lobe. He deteriorated before making an almost complete recovery 24 days later, with only a few issues with memory loss and temper control as a result. He lived for 12 more years.


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Does the brain have localised areas of function?

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Yes.

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What is the motor cortex?

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The motor cortex is the area of the brain that's most involved in controlling your voluntary movements (from planning to executing them). It is the primary motor area of the brain. 

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Who conducted a study on a dog to identify the motor areas of the brain?

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Gustav Fritsch and Eduard Hitzig in 1870 

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What two areas is the motor cortex divided into?

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The primary motor cortex and the nonprimary motor cortex. 

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What are the two areas the nonprimary motor cortex divides into?

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The premotor cortex and the supplementary motor cortex.

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What did Dr Penfield develop during his experiments in the field of neurophysiology?

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The motor homunculus. 

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