LOCALISATION OF FUNCTION IN THE CEREBRAL CORTEX
Localisation of function in the brain, motor, somatosensory, visual, auditory and language centres; Broca’s and Wernicke’s areas
Cerebrum: The cerebrum, also known as the telencephalon, is the largest and most highly developed part of the human brain. It encompasses about two-thirds of the brain mass and lies over and around most of the brain's structures. The cerebrum is divided into right and left hemispheres that are connected by the corpus callosum. The outer portion (1.5mm to 5mm) of the cerebrum is covered by a thin layer of grey tissue called the cerebral cortex. The term is sometimes INCORRECTLY extended to refer to The entire brain.
The Cortexes
Cerebral Cortex (also sometimes called the Neo cortex): THE Cerebral Cortex is a thin-layered structure surrounding mammalian brains. It is the hallmark of mammalian brains and is not present in birds or in reptiles. It is also the most divergent part across mammalian species It is sometimes called "neo", because it is evolutionarily the newest part of the cereberal cortex. Some people prefer to call it the "Iso Cortex" because it sounds more neutral. The “Cerebral cortex" is almost synonymously used as Neo Cortex, although the term Cerebral Cortex includes the Hippocampus and Rhinal Cortex, in addition to Neo Cortex. Just "cortex" usually means the same thing as the cerebral cortex. If you compare the brains of mice, monkeys, and humans (SEE THE PICTURE BELOW), you can see that the size and outlook of the three brains are very different. The different outlook is attributable to the Neo Cortex. The cerebral cortex is the most recent part of the brain to develop, in Latin it literally means “new bark. Humans, dolphins and primates have been found to have the most neocortical neurons.
The human cerebral cortex is 2-4 mm (0.08-0.16 inches) thick and comprises six layers, labelled from the outermost inwards, I to VI. In humans, the Cerebral Cortex is involved in higher functions such as sensory perception, generation of motor commands, spatial reasoning and language, There are two types of cortex in the neocortex – the true isocortex and the proisocortex.
While the Cerebral Cortex is smooth in rats and some other small mammals, it has deep grooves (sulci) and wrinkles (gyri) in primates and several other mammals. These folds serve to increase the area of the neocortex considerably. In humans, it accounts for about 76% of the brain's volume.
The Brain Lobes
LOCALISATION OF FUNCTION IN THE BRAIN
Localisation of function: The human brain is undoubtedly the most complex and remarkable structure within the body. It has around 100 billion neurons and around 100 trillion synapses!
Different areas within the brain are responsible for specific functions. This is called the localisation of function. The theory of localisation of function suggests that there are functionally specialised regions in the brain that are domain-specific for different cognitive processes. Jerry Fodorcreated the Modularity of the Mind theory. The Modularity of the Mind theory indicates that distinct neurological regions called modules are defined by their functional roles in cognition. An example of Fodor's concept of modules is seen in cognitive processes such as vision, which have many separate mechanisms for colour, shape and spatial perception.
One of the fundamental beliefs of localisation of function and the theory of modularity suggests that it is a consequence of natural selection and is a feature of our cognitive architecture.
Prefrontal Cortex
Problem-Solving, Emotion, Complex Thought
Motor Association Cortex
Coordination of complex movement
Primary Motor Cortex
Initiation of voluntary movement
Primary Somatosensory Cortex
Receives tactile information from the body
Sensory Association Area
Processing of multisensory information
Visual Cortex
Complex processing of visual information
Visual Cortex
Detection of simple visual stimuli
BROCA’S AREA
Speech production and articulation
Where is it? The left hemisphere, frontal lobe. The motor region, located in Broca’s area, is close to the area that controls the mouth, tongue and vocal cords.
What is it? Responsible for the production of language
What kind of research? Postmortem, scans, split-brain research, electrical stimulation in surgery
RESEARCH ON LOCALISATION OF THE LANGUAGE CORTICES
What kind of research? Postmortem, scans, split-brain research, electrical stimulation of humans only (why?) in surgery only (again, why?).
1825: Jean-Baptiste Bouillaud presents cases of loss of speech after frontal lesions
1836: Marc Dax reads a paper on left hemisphere damage effects on speech
1860: Paul Broca discusses cortical localisation of language production:
Named after Paul Broca, French neurosurgeon
Treated a patient called ‘Tan’ – unable to speak other than this one word (but did understand language). I studied 8 other patients who had similar language deficits, along with lesions in their left frontal hemisphere. Patients with damage to their right frontal hemisphere did not have the same problems. This led him to identify the existence of a language centre in the back portion of the frontal lobe of the left hemisphere (Broca 1865) believed to be critical for speech production.
HOWEVER, neuroscientists have found that when people perform cognitive tasks (nothing to do with language) their Broca area is active
Fedorenko (2012) discovered two regions of Broca’s area – one selectively involved in language, the other involved in responding to many demanding cognitive tasks (such as performing maths problems)
1864: John Hughlings Jackson writes on loss of speech after brain injury
1874 - Carl Wernicke publishes Der Aphasische Symptomen complex on aphasias:
German neurologist Carl Wernicke discovered another area of the brain that was involved in understanding language as patients with lesions on the back portion of their left temporal lobes (Wernicke’s area) could speak but were unable to understand language.It is proposed that language involves separate motor and sensory regions located in different cortical regions.
The motor region, located in Broca’s area, is close to the area that controls the mouth, tongue and vocal cords. The sensory region, located in Wernicke’s area, is close to the regions of the brain responsible for auditory and visual input. Input from these regions transferred to Wernicke’s area when recognised as a language and associated meaning.
There is a neural loop (arcuate fasciculus) running between Broca’s area and Wernicke’s area; at one end lies Broca’s area – responsible for the production of language. At the other lies Wernicke’s area – responsible for the processing of spoken language.
Brain scans also showed most participants have these language cortical maps.
THE LANGUAGE CIRCUIT
Wernicke's Area
Language comprehension
Auditory Association Area
Complex processing of auditory information
THE AUDITORY CIRCUIT
Detection of sound quality (loudness, tone)
The auditory area is located in the temporal lobe and is responsible for analysing and processing acoustic information. Information from the left ear goes primarily to the right hemisphere, and information from the right ear goes primarily to the left hemisphere. The auditory area contains different parts, and the primary auditory area is involved in processing simple sound features, including volume, tempo and pitch.
Motor Cortex:
Location: frontal lobe along the bumpy region of the precentral gyrus
Responsible for the generation of voluntary motor movements
On both hemispheres – the motor cortex on the right hemisphere controls muscles on the left side of the body and vice versa
Different parts of the motor cortex control different parts of the body. These are arranged logically – the region that controls the foot is next to the region that controls the leg.
RESEARCH ON LOCALISATION OF THE MOTOR CORTEX
What kind of research? Postmortem, scans, split-brain research, electrical stimulation in humans and animals, ablations and lesions.
1809: Luigi Rolando (1773–1831) first used galvanic current to stimulate the cortical cortex of animals, as he stimulated certain areas the dog would move that body part.
In 1870, Eduard Hitzig and Gustav Fritsch discovered the cortical motor area of dogs using electrical stimulation.
1872 David Ferrier (1843–1924) identified a monkey’s cerebral cortex points whose stimulation was related to specific animal movements.
1874 - Roberts Bartholow electrically stimulates human cortical tissue.
1875 - Sir David Ferrier describes different parts of the monkey's motor cortex.
1882, the Italian neuropsychiatrist Ezio Sciamanna performed a series of systematic experiments of electrical stimulation on a trepanned patient who had a traumatic brain injury
Sir Victor Horsley publishes a somatotopic map of a monkey's motor cortex.
1957 - W. Penfield and T. Rasmussen devise motor and sensory homunculus brain stimulation of the human cortex that could give a real accurate representation of the human brain functions, including motor and somatosensory areas (cortical homunculus, Penfield and Boldrey.
Brain scans also showed most participants have this motor cortical map.
THE SOMATOSENSORY CORTEX
The somatosensory cortex is a part of the brain that is primarily responsible for processing sensory information from the body. This includes sensations like touch, temperature, pain, and proprioception (the sense of the relative position of one's body parts).
In humans, the somatosensory cortex is located in the parietal lobe, typically in an area called the postcentral gyrus, which lies just behind the central sulcus, a prominent fold in the brain's surface. This region is organized somatotopically, meaning that different parts of the somatosensory cortex correspond to sensations from different body parts. This organization is often depicted as a "sensory homunculus," a distorted representation of the body with the size of each body part reflecting the amount of cortical area devoted to it. For instance, the hands and lips, which have a high density of sensory receptors, take up a disproportionately large area of the somatosensory cortex compared to their physical size.
The primary somatosensory cortex (often denoted as S1) is the main recipient of sensory input, but there are also secondary somatosensory areas (like S2) that further process this information and contribute to our perception of touch and proprioception. These areas are important for integrating sensory input and enabling complex functions like identifying objects by touch, perceiving the texture of surfaces, and coordinating movement with sensory feedback.
What kind of research? Postmortem, scans, split-brain research, electrical stimulation in surgery
Location: (Behind the frontal lobe in the Parietal lobe - along a region called the post-central gyrus)
Detects sensory events from different regions of the body
Dedicated to the processing of sensory info related to touch
Uses sensory info from the skin to produce sensations such as touch pressure, pain, and temperature which it then localises to specific body regions
Both hemispheres have a somatosensory cortex
The cortex on one side of the brain receives sensory info from the opposite side of the body.
Topographical Map.
RESEARCH ON LOCALISATION OF THE SOMATOSENSORY CORTEX
1871 - Silas Weir Mitchell provides coins the term phantom limb syndrome and provides a detailed account of the condition.
1909 - Harvey Cushing is the first to electrically stimulate the human sensory cortex: 41 patients underwent cortical stimulation for intra-operative motor mapping. Cushing used cortical stimulation to define primary motor and sensory cortices in the treatment of tumours, trauma, and epilepsy within adult and paediatric populations.
1957 - W. Penfield and T. Rasmussen devise motor and sensory homunculus brain stimulation of the human cortex that could give a real accurate representation of the human brain functions, including motor and somatosensory areas (cortical homunculus, Penfield and Boldrey.
A phantom limb is the sensation that an amputated or missing limb is still attached. Approximately 80 to 100% of individuals with an amputation experience sensation in their amputated limb. However, only a small percentage will experience painful phantom limb sensations. These sensations are relatively common in amputees and usually resolve within two to three years without treatment. For many years, the dominant hypothesis for the cause of phantom limbs was a pinched nerve. This was proved incorrect. According to Melzack, the experience of the body is created by a wide network of interconnecting neural structures; this is now known as the somatosensory cortex.
Pons and colleagues (1991) at the National Institutes of Health (NIH) showed that the primary somatosensory cortex in macaque monkeys undergoes substantial reorganisation after the loss of sensory input.
In other words, if this area does not receive input from the environment, say for example, stopping a monkey from feeling any sensations on their fingers, then the area of the somatosensory cortex dedicated to sensations in the fingers will be pruned out and reorganised.
This is the case in human participants. For example, in case studies of amputees who have lost a hand, the cortical map representing the hand reorganises itself after a few months. It does this by moving the area for “finger sensation” to the adjacent area on the somatosensory cortex; please look at the map below; which area is next to the hand?
You should have noted that the area next to the hand on the somatosensory cortex is the face. This means that amputees still felt their lost hand but only when somebody touched their face.
Vilayanur S. Ramachandran hypothesised that phantom limb sensations in humans could be due to reorganisation in the human brain's somatosensory cortex. Ramachandran and colleagues illustrated this hypothesis by showing that stroking different parts of the face led to perceptions of being touched on different parts of the missing limb.
This is because the area representing the hand was no longer receiving input from the outside world, who could it; the hand no longer existed. For the brain to keep the representation of a hand in its map, it had to reorganise its map.
Later brain scans of amputees showed the same kind of cortical reorganisation.
Brain scans also showed most participants have this somatosensory cortical map.
Note, you can’t really research animals unless you are testing for loss of pain; why?
TOPOGRAPHICAL MAPS
These maps may be thought of as a mapping of the surface of the body onto the brain structure. Like mapping out how touch or motor ability would be represented in the brain. How much space, for example, does the brain dedicate to the sensory area of the fingers compared to the back? Phrased another way, topographic maps are organised in the neural system in a manner that is a projection of the sensory surface onto the brain.
Examples
Wilder Penfield discovered the original topographic map of the sensory cortex in the form of his Homunculus man (see below). His work on human neural systems showed that the brain areas that process tactile sensations are mapped in the same fashion that the body is laid out. This sensory map exaggerates certain regions with many peripheral sense cells, like the lips and hands, while reducing the relative space for processing areas with few receptors, like the back.
Homunculus Man
THE VISUAL CORTEX
At the back of the brain, in the occipital lobe is the visual area, which receives and processes visual information. Information from the right-hand side visual field is processed in the left hemisphere, and information from the left-hand side visual field is processed in the right hemisphere. The visual area contains different parts that process different types of information including colour, shape or movement.
What kind of research? Postmortem, ablations, Scans, split-brain research, electrical stimulation in surgery
RESEARCH ON LOCALISATION OF THE VISUAL CORTEX
1855: Bartolomeo Panizza shows the occipital lobe is essential for vision.
1881: Hermann Munk reports on visual abnormalities after occipital lobe ablation in dogs
1947 - German neurologist Joachim Bodamer coined "prosopagnosia" (face blindness).
1981 - David Hunter Hubel and Torsten N. Wiesel-Nobel Prize-visual system
Brain scans also showed most participants have this visual cortical map.
DISCUSS LOCALISATION OF FUNCTION IN THE CEREBRAL CORTEX ESSAY
MARKS = 16 MARKS
A01 = 6 = outline and description
A03 = 10 = evaluate
SPECIFICATION SAYS:
Localisation of function in the brain: motor, somatosensory, visual, auditory and language centres; Broca’s and Wernicke’s areas
COMMAND WORDS:
Discuss = A01 & A03, e.g., outline and evaluate
STEP ONE: EXPLAIN THE ESSAY TITLE
The cerebrum is the largest part of the brain; the cerebral cortex is the ¼ inch think outside layer of the cerebrum, it the home of all higher cognitive functions.
Localisation of function in the brain means to pinpoint or locate higher cognitive functions such as language, voluntary movement and sensations in the cerebral cortex. Are these functions always in the same place? Would damage to a particular area cause a function to be lost?
STEP TWO: DESCRIBE A LOCALISED AREA
PICK 2-3 FROM THE FOLLOWING AS DETAILED ON THE SPECIFICATION: Remember, although five areas of localisation are listed on the specification, you don’t have to discuss them all in the above essay. It is assumed you will choose depth - 1-2 theories versus breadth- 3-4 theories in the Ao1.
1. Motor cortex
2. Somatosensory cortex
3. Language cortices: Broca and Wernicke
4. Visual cortex
5. Auditory cortex.
FOR EACH AREA YOU NEED TO KNOW:
1. What is the function for?
2. What kind of research? Postmortem, scans, split-brain research, electrical stimulation in surgery etc.
3. Where is the function located in the cortex?
A01 is an account, an outline, or a description of a theory or a piece of research (APFC). You report the essence of a theory or piece of research using appropriate terminology. No evaluation here.
A01:
The cerebrum is the largest part of the brain; the cerebral cortex is the ¼ inch think outside layer of the cerebrum, it is home to all the higher intellectual abilities in mammals. Localisation of function in the brain means to identify these higher cognitive functions, for example language, voluntary movement and physical sensation and locate their position on the cerebral cortex. Also integral to this theory is investigating whether these functions are always in the same place for all members of a species and exploring how disease in a particular area affects that function, e.g., is the function lost forever if it is damaged?
One major area thought to be localised is language. In the 1800s, a physiologist named Paul Broca discovered what he thought was the area for memorising speech sounds (spoken language) when he performed a post-mortem on a patient who had lost the ability to talk. The patient, nicknamed “Tan” because that is all he could say, had damage to the left frontal lobe of the cerebral cortex.
Not long after this, another area of speech was localised by a researcher named Wernicke. He discovered what he thought was a “speech comprehension system” on the left temporal lobe of the cerebral cortex after performing a post-mortem on a patient who could no longer understand spoken language.
In conjunction with locating language, other major functions have been localised, such as the somatosensory (SS) area, which is located along the front strip of the parietal lobe. The SS cortex is dedicated to sensory and tactile information and is arranged topographically across both hemispheres. The left half of the brain controls the right half of the body and vice versa.
Just adjacent to the somatosensory cortex is the motor cortex, located along the back strip of the frontal lobe and responsible for all voluntary movements. This area was discovered through various research procedures, such as electrical stimulation (mimicking the brain’s action potentials) and ablations (cutting away the area of cortical tissue and then observing the effects. Like the SS, the motor cortex is also systemically organised, and the amount of cortical space dedicated to each body part is correlated to how dexterous that body part is.
A03 Evaluation
Identify your arguments and points.
Evaluate research
Generalisability: Left-handers, non-typical Brains Gender, Accidents/ Plasticity
Distributed parallel functions versus localisation.
Evolutionary adaptive reason for localised areas.
Applied to the real world, e.g., knowing where brain functions are in the cerebral cortex is helpful because …
Any issues or debates
EVALUATION OF RESEARCH METHODS
The problem with using ablations is you can’t generalise to the wider population. Wrong x (not applied – shopping list point).
Using: point evidence/ explain/ evaluate and link back to the question (what is the essay question?)
Identify the PEEL points below:
The problems with using methods such as ablations and post-mortems is that participants such as Paul Leborgne aka “Tan” may have individual differences in brain organisation, for example “Tan” may have a larger speech area than other people, especially if the person was bilingual for example. It may, therefore, not be possible to generalise the findings from Tan to other people. Moreover, post-mortems do not show real-time activity in the brain as the person is dead. Similarly, ablations are not a precise research tool, cuts may have different consequences on different brain organisations. However, since this time much more advanced methods of investigating the brain have been introduced, for example electrical stimulation, this method is more precise as it can pinpoint smaller detail such as the topographical maps in the motor and sensory cortices. However, as animals are its main targets, it’s also difficult to generalise as animals have different motor systems, e.g., tails. Lastly, the introduction of scans is the most robust evidence of localisation because …. Scans can use human participants, 1000s of participants can be recruited, it’s not invasive, scans look at real-time brain activity (not dead brains)
This means that researchers can confidently assume most people have functions organised or localised in the same places.
COMPLETE EVALUATION
Evaluating Localisation of Function
SUMMING UP THE RESEARCH ON LOCALISATION OF BRAIN FUNCTION The problem with using research methods that use case studies, ablations and post-mortems is that participants such as Paul Leborgne aka “Tan” may have individual differences in brain organisation, for example, “Tan” may have had a larger speech area than other people, especially if before his injury he could speak another language or was bilingual, for example. It is, therefore, not possible to generalise the findings from Tan to other people. Moreover, post-mortems do not show real-time activity in the brain as the person is dead. Similarly, ablations are not a precise research tool, cuts may have different consequences on different brain organisations and different animals.
From the nineteenth century, much more advanced methods of investigating the brain have been introduced, for example, electrical stimulation; this method is more precise as it can pinpoint smaller details such as the topographical maps in the motor and sensory cortices. However, as animals are its main targets, it’s also difficult to generalise to humans as animals have different motor systems, e.g., they have tails and whiskers. Animals also have different somatosensory systems, e.g., no colour vision, better smell and hearing so generalisability is problematic.
However, since the 1990s, localisation of function in the cerebral cortex has been supported by neuroimaging studies. Scans are a much more advanced technique than any of the other methods as they can use 1000s of atypical human participants. Moreover, scans are not invasive and look at real-time brain activity (not dead brains). Moreover, here is a wealth of case studies on patients with damage to Broca’s and Wernicke’s areas that have demonstrated their functions. For example, Broca’s aphasia is an impaired ability to produce language; in most cases, this is caused by brain damage in Broca’s area. Wernicke’s aphasia is an impairment of language perception, demonstrating the important role played by this brain region in language comprehension. This means that researchers can confidently assume most people have functions organised or localised in the same places.
LEFT HANDERS One of the main issues with the localisation of function is that not all people have the same brain arrangement. For example, 40% per cent of left-handers have opposite brain organisation, e.g., Broca’s area is in the right hemisphere, and the visual-spatial area is in the left hemisphere. Furthermore, even though 60-70% of left-handers use the left side of the brain for language, they will still have different neural organisations because their brain has to double-wire the information across both hemispheres. Different mapping will also apply to the small proportion of left-handers who have a bilateral organisation of language. In summary, this means that the theory of localisation will not apply to most left-handers and to some right-handers.
NON-ATYPICAL BRAINS Similarly, congenitally blind and/or deaf people will have developed different auditory and visual cortices because of their disabilities. Primary functions such as the auditory and visual cortex will not be the same for these people as their brains will have pruned areas not receiving stimulation or recruited for their intact senses.
MALE VERSUS FEMALE BRAINS Lastly, there are thought to be differences in the size of Broca’s area in males and females. A study led by G. Pearlson has shown that two areas in the frontal and temporal lobes related to language were significantly larger in women, thus providing a biological reason for women's superiority in language. Using magnetic resonance imaging, the scientists measured grey matter volumes in several cortical regions in 17 women and 43 men. Women had 23% more volume than men in Broca's area and 13% greater volume in Wernicke's area, These results were later corroborated by another research group from the School of Communication Disorders, University of Sydney, Australia, which was able to prove these anatomical differences in the areas of Wernicke and of Broca, the volume of the Wernicke's area was 18% larger in females compared with males, and the cortical volume the Broca's area in females was 20% larger than in males. Moreover, additional evidence comes from research showing that the corpus callosum, a large tract of neural fibres which connect both brain hemispheres, is enlarged in women, compared to men although this discovery has been challenged recently. All the above differences mean that localisation of function cannot accurately predict the layout of male versus female brains. A level of beta bias in the theory: the differences between men and women are ignored, and variations in the pattern of activation and the size of areas observed during various language activities are not considered
PLASTICITY Another factor that thwarts the theory of localisation is functional plasticity. Functional plasticity is the mechanism that causes the brain to adapt to injury, e.g., it refers to the brain’s ability to move functions from a damaged area of the brain to non-damaged areas (often in the other hemisphere or adjacent areas of the damaged brain – this means that intact areas of the cortex could take over responsibility for specific cognitive functions following brain injury. This, therefore, casts doubt on theories about the localisation of functions, suggesting that functions are not localised to just one region, as other regions can take over specific functions following brain injury.
ALTERNATIVE THEORIES The claim that functions are localised to certain brain areas has been criticised. Lashley proposed the equipotentiality theory, which suggests that the basic motor and sensory functions are localised, but that higher mental functions are not. Psychologists suggest that it is more important to investigate how the brain areas communicate with each other, rather than focusing on specific brain regions. Wernicke claimed that although the different areas of the brain are independent, they must interact with each other to function. An example to demonstrate this is a man who lost his ability to read, following damage to the connection between the visual cortex and the Wernicke’s area. This suggests that interactions between different areas produce complex behaviours such as language. Therefore, damage to the connection between any two points can result in impairments that resemble damage to the localised brain region associated with that specific function. This reduces the credibility of the localisation theory.
This alternative theory to localisation of function is called the distributive processing model.. This theory proposes that the brain is more interactive, and its regions are functionally interconnected. It argues that the localised, specialised areas are almost irrelevant as multiple brain regions must combine to complete a behaviour. Because the cerebral cortex is a highly complex, heavily interconnected system, it could be argued that it is hard to localise a function to a specific structure in the brain since the structures are linked. In truth, cortex regions, configure connections and reconconfigure connections to multiple areas in the cortex - depending on the required behaviour.
Also, critics argue that localisation theories are biologically reductionist and try to reduce very complex human behaviours and cognitive processes to one specific brain region. Such critics suggest that a more thorough understanding of the brain is required to truly understand complex cognitive processes like language.
REASON FOR EVOLUTIONARY ADAPTION
Explanations for the evolution of the human cerebral cortex mainly focus on the selection pressures of the physical and social environment, e.g., climate, diet, food availability, sexual selection, group size, coalition formation and parental care. Hunting in groups possibly necessitated the development of language. Evolutionary researchers propose that the human mind evolved because of natural selection. Therefore, modules such as Broca’s area would have developed in response to selective pressures and increased chances of survival, e.g., "fit" behaviour.
APPLICATION TO THE REAL WORLD
Future developments for localisation of function theories may lie in "modular psychiatry". The concept is that a modular understanding of the brain and advanced neuro-imaging techniques will allow for a more practical diagnosis of mental and emotional disorders. For example, schizophrenics often have problems with Broca’s area.
CRITICISMS
Broca believed Broca’s area to be critical for speech production. HOWEVER, However, although there is evidence from case studies to support the function of Broca’s and Wernicke’s areas, more recent research has provided contradictory evidence. Dronkers et al. (2007) conducted an MRI scan on Tan’s brain, to try to confirm Broca’s findings. Although a lesion was found in Broca’s area, they also found evidence to suggest other areas may have contributed to the failure in speech production. Moreover, other neuroscientists have found that when people perform cognitive tasks (nothing to do with language) their Broca area is active. Fedorenko (2012) discovered two regions of Broca’s area – one selectively involved in language, the other involved in responding to many demanding cognitive tasks (such as performing maths problems. These results suggest that Broca’s area may not be the only region responsible for speech production, and the deficits found in patients with Broca’s aphasia could result from damage to other neighbouring regions.
A SHORT EXAMPLE OF OTHER POSSIBLE WAYS TO WRITE A01 and A03.
Instead of writing all A01 and A03, you can intersperse them.
Localisation of function is the idea that certain functions (e.g., language, memory, etc.) have certain locations or areas within the brain.
An important area thought to be localised is voluntary movement. From the 1700s various physiologists had discovered what later became known as the motor cortex by ablating - which is essentially removing cortical tissue from various animals and then observing which area became defunct when the animal became conscious.
Researchers observed that when they ablated the back strip of the frontal lobe, it always resulted in a loss of some motor function. As ablations became more refined, e.g., removing smaller areas of brain tissue, researchers could build up a more detailed record of how the brain represented the body in the cortex into what later became known as the topographical map. It was also discovered that anatomy that has more dexterity, e.g., fingers and tongue has more cortical tissue dedicated to it.
Similar research methods were used to discover the location of the somatosensory cortex, the home to all tactile information., e.g., ablations post-mortems.
However, using electrical stimulation in localisation research meant that data from living humans could be used. For example, in operations where tumours are removed, neurosurgeons need to stimulate or block neural pathways to identify important areas that should not be cut away, e.g., parts of the somatosensory cortex so it’s not removed along with the tumour. Such procedures have shown that humans can feel different sensations in parts of their bodies when researchers stimulate the anterior portion of the parietal lobe with electricity.
Furthermore, amputees with phantom limb ideation have also been used to prove the existence of the somatosensory cortex. The amputated limb is still represented in the brain’s topographical map despite it no longer being physically represented on the body. Therefore, amputees can still feel their missing limbs because their brain still represents their existence in their body map.