TYPES OF RESEARCH USED: FOR LOCALISATION OF FUNCTIONS
KEYWORDS FOR: LOCALISATION OF BRAIN FUNCTION
AUDITORY CORTEX: Located in the temporal lobe, it processes auditory information.
CORTEX: General term for the outer layer of the brain's regions involved in processing information.
CEREBRUM: The most significant part of the brain, including the cerebral cortex, is responsible for higher-order functions.
CEREBRAL CORTEX: The outermost layer of the brain, responsible for higher cognitive functions.
COGNITIVE NEUROLOGIST: A specialist who studies how brain damage or neurological disorders affect cognitive functions like memory, language, and decision-making.
BRAIN LOBES: The four main lobes of the brain, each associated with specific functions:
BROCA’S AREA: A region in the frontal lobe associated with speech production.
FRONTAL LOBE: Responsible for reasoning, problem-solving, and motor control.
PARIETAL LOBE: Processes sensory information and spatial awareness.
DISTRIBUTED PROCESSING: The concept that brain functions are not isolated but depend on networks of interconnected regions working together.
EQUIPOTENTIALITY THEORY: This theory suggests that while some basic functions may be localised, higher cognitive functions are more distributed across the brain.
HOMUNCULUS MAN: A visual representation of how different body parts are mapped onto the somatosensory and motor cortices according to the amount of control or sensory input they receive.
LOBES VS CORTICES: Lobes are the broader regions of the brain (e.g. frontal, temporal), while cortices are specialised areas within the lobes that handle specific tasks, such as the visual cortex for vision.
LOCALISATION OF FUNCTION: The theory that some regions of the brain are specialised for specific functions, such as language or movement.
MOTOR CORTEX: Controls voluntary movements and is located in the frontal lobe.
NEOCORTEX is the newest and most significant part of the cerebral cortex. It comprises approximately 90% of the human cortex and has six distinct layers.
NEUROIMAGING: Techniques such as fMRI and PET scans allow scientists to visualise brain activity and better understand the distribution of functions across different brain regions.
OCCIPITAL LOBE: Primarily involved in visual processing.
PHANTOM LIMB: The phenomenon where individuals who have had a limb amputated continue to feel sensations, including pain, in the missing limb, due to the brain’s sensory map.
PHRENOLOGY: A now-debunked theory that claimed the shape of the skull could determine personality traits and cognitive abilities by mapping bumps on the head.
POST-MORTEM: The examination of a body after death to determine the cause of death or study specific conditions, often used in brain research to examine the effects of brain damage on function.
PREFRONTAL CORTEX: The region at the front of the frontal lobe, associated with decision-making, personality, and social behaviour.
TEMPORAL LOBE: Key for auditory processing and memory functions.
SOMATOSENSORY CORTEX: Located in the parietal lobe, it processes somatosensory inputs from the body, including touch, pressure, and pain.
TOPOGRAPHICAL MAPPING: Refers to the way the brain organises the body's sensory and motor functions in a map-like representation, as seen in the motor and somatosensory cortices.
VISUAL CORTEX: Located in the occipital lobe, it processes visual information like shape, colour, and motion.
WERNICKE’S AREA: A region in the temporal lobe responsible for language comprehension
Before we delve into the different areas of the brain whose locations and functions have been identified, it is useful to familiarise yourself with the research methods used in this field. This is because much of what we know about localisation of function has come from the methods scientists have used to study the living and damaged brain. Each technique—whether post-mortem examination, electrical stimulation, lesion and ablation studies, psychosurgery, or modern brain imaging—has contributed unique insights into how specific cortical regions control particular behaviours. Understanding how this evidence was gathered will make it easier to evaluate the strengths and limitations of localisation research later on
CASE STUDIES
When first glancing over the range of techniques used to study localisation of brain function, the list appears diverse — and it is. Post-mortem examinations, electrical stimulation, ablations and lesions, psychosurgery, accidents, disease, EEGs, and modern brain scans have all contributed to mapping the brain. Each method tells part of the same story but from a different angle, revealing how specific areas of the neocortex control movement, sensation, vision, and language.
Although these techniques differ in precision and purpose, they all fall under the broad category of case-based research. This does not mean that a case study is itself a scientific method in the way that fMRI, EEG, or post-mortem analysis are. Instead, it describes the nature and scale of the data — usually small or unique samples — and the conditions under which the research can be ethically conducted. Case studies are idiographic by definition, concerned with individual or rare examples rather than with large, statistically tested groups. In the humanities and social sciences, this may be deliberate and phenomenological, focusing on lived experience and depth of description. In neuroscience, however, it is usually a matter of necessity: direct experimental manipulation of the human brain is impossible, so researchers must rely on naturally occurring opportunities provided by injury, illness, or surgery.
Historically, case-based evidence has combined a range of scientific techniques. Earlier work used post-mortem examination, crude ablation and lesion studies, and forms of psychosurgery carried out before the structure of the cortex was fully understood. These early methods were often imprecise but produced the first observable links between cortical damage and behavioural deficits. With advances in technology, the field expanded to include electrical stimulation during surgery, EEGs to record electrical activity, and later PET, MRI, and fMRI scanning to visualise activity in the living brain. Each method contributes differently: post-mortem analysis reveals structure after death; scanning reveals function in real time; lesions and psychosurgery provide causal inference about what happens when an area is disrupted.
Because of ethical and practical constraints, large-scale nomothetic studies are rarely possible in localisation research. Instead, a cumulative idiographic record has been built from hundreds of individual cases, each adding detail to the cortical map. In this sense, the case study operates as an umbrella framework that integrates multiple investigative tools — post-mortem analysis, neuroimaging, stimulation, and surgical observation — to examine how structure relates to function. Together, these diverse methods have provided converging evidence that the brain is functionally specialised yet interconnected.
FAMOUS HUMAN CASE STUDIES
While Broca’s and Wernicke’s patients are discussed elsewhere in relation to language, their cases also demonstrated links with the motor and sensory cortices. Broca’s area lies adjacent to the motor cortex and controls the movements of the lips, tongue, and jaw involved in speech production, showing how language function overlaps with motor control. Wernicke’s area, located in the temporal lobe near the auditory cortex, is closely associated with sensory processing and enables comprehension of spoken language.
MOTOR FUNCTION AND ACCIDENT CASES
Injury-based case studies — such as those involving car, motorcycle, or industrial accidents — have frequently revealed a direct relationship between damage to the motor cortex and loss of movement. Patients with frontal-lobe injuries that included the precentral gyrus often showed paralysis or loss of fine motor control in the body parts represented by the damaged area. These effects were contralateral — for example, right-hemisphere damage led to loss of movement on the left side of the body. This supports localisation of voluntary movement to the motor cortex.
SOMATOSENSORY FUNCTION AND TRAUMA CASES
Similar patterns have been observed in parietal-lobe injuries resulting from falls, collisions, or blows to the head. Damage to the postcentral gyrus produced loss of tactile sensation, numbness, or an inability to distinguish between pressure and texture in the corresponding body region. Modern neuroimaging and post-mortem analyses have confirmed that these sensory deficits map precisely onto the area of cortical damage, reflecting the somatotopic organisation of the somatosensory cortex.
VISUAL FUNCTION AND ACCIDENTAL INJURY
Head injuries to the occipital lobe — often from car or sports accidents — have been linked to visual field loss or cortical blindness. Patients may lose vision in specific regions of the visual field while retaining other areas, depending on which region of the visual cortex is damaged. Post-mortem and modern neuroimaging studies confirm that these deficits follow a retinotopic pattern, meaning the visual field is mapped systematically across the cortex.
H.M. (1953) — ABLATION AND MEMORY LOSS
Henry Molaison (H.M.) underwent bilateral ablation (surgical removal) of the hippocampus to treat epilepsy. Although the operation was successful in controlling seizures, it caused permanent loss of the ability to form new long-term memories. H.M.’s case is distinct from traumatic injuries, as it involved deliberate surgical removal rather than accidental damage. Still, it provided robust evidence that the hippocampus is localised for memory formation rather than perception, movement, or sensation.
PHINEAS GAGE – A NOTE OF CAUTION
Phineas Gage is one of the most famous examples used to illustrate localisation of brain function. In 1848, an explosion drove a metre-long iron rod through his skull, destroying much of his left frontal lobe. Remarkably, Gage survived, but reports described a profound change in his personality and behaviour — from responsible and even-tempered to reckless, impulsive, and socially inappropriate. His case provided early evidence that specific brain regions are associated with distinct psychological functions, explicitly demonstrating the frontal lobe’s role in regulating personality, planning, and emotional control.
However, while Gage’s case is frequently cited in psychology textbooks as evidence of localisation, it should be used with caution. The AQA specification focuses on sensory, motor, and language areas — specifically the motor, somatosensory, visual, and Broca’s and Wernicke’s regions. The frontal cortex is not explicitly required for this topic. Therefore, Gage’s case is best used to illustrate the concept of localisation as a whole rather than as direct evidence for these specific cortical areas.
POST-MORTEM (AUTOPSY) STUDIES
TIME PERIOD:
Early 1800s – Present
PURPOSE:
To study the brains of deceased individuals and identify which areas were responsible for specific abilities or behaviours. Researchers examined structural damage and linked it to behavioural or cognitive symptoms recorded during the person's lifetime.
CONTEXT AND USE:
Before the development of scanning technologies, post-mortem studies were the primary method for investigating the localisation of function. Clinical notes taken during the person’s life were compared with the pattern of damage found at autopsy. From this, scientists inferred which brain regions were associated with specific abilities such as speech, movement, or vision.
WHAT IT SHOWED:
Postmortem work provided the first anatomical evidence that specific areas of the cortex are associated with particular functions. For example, damage to the left frontal region was consistently associated with loss of speech production, while damage to the occipital lobe was linked with visual impairment. It also revealed that the brain operates contralaterally — meaning each hemisphere controls the opposite side of the body.
LIMITATIONS:
Post-mortem studies are descriptive and retrospective. They cannot show the brain functioning in real time or explain precisely how the damage produced the behavioural change. Every brain is structurally unique, and lesions rarely occur in isolation, so results cannot be generalised. The approach also assumes that changes seen after death reflect what was true during life, which is not always the case.
WHY IT DECLINED:
Advances in neuroimaging now allow researchers to observe brain activity in living individuals safely and repeatedly, using larger and more controlled samples. However, post-mortem analysis remains valuable for confirming structural findings, examining cellular and microscopic anatomy, and verifying imaging results.
INVASIVE METHODS OF INVESTIGATING THE BRAIN: ABLATIONS AND LESIONS
TIME PERIOD 1820s – 1960s
Ablations involve the surgical removal of large sections of the cortex, often performed in early research when little was known about brain function. Researchers used scalpels or blunt instruments to remove entire regions, then observed the resulting behavioural deficits. For example, removing the entire visual cortex rendered animals blind. However, this did not account for finer deficits, such as the inability to perceive movement or to recognise faces. Ablation was stopped once it was realised that cortical tissue contains approximately 30 million neurons per cubic millimetre, making the technique too crude to reveal detailed information. Lesions are minor, targeted injuries created using heat, chemicals, or electrical current to damage specific neural sites. Both methods were used to localise brain function by comparing behavioural changes before and after damage, revealing which cortical areas controlled movement, sensation, and vision.
Both methods were used in animal research to examine causal links between brain areas and behaviour. By removing or damaging parts of the cortex and observing the resulting deficits, researchers identified distinct functional regions: motor ablations produced paralysis or loss of coordination, parietal lesions impaired tactile discrimination and spatial awareness, and occipital damage caused visual blindness. These studies provided experimental support for the localisation of function and informed later human neuropsychological and neuroimaging research.
ABLATIONS: When large sections were ablated, animals often lost entire functions, such as movement, touch, or vision, demonstrating that these abilities were localised to specific cortical areas. This provided the first experimental evidence that brain functions are not evenly distributed across the cortex but are concentrated in specialised regions, laying the foundation for later human studies using neuropsychology and brain imaging.
MOTOR CORTEX: When specific parts of the motor cortex were ablated, the body parts controlled by those regions became paralysed or lost coordination. This showed that the motor cortex controls voluntary movement and that each section corresponds to a particular body region — a relationship known as somatotopic organisation. Recovery was often limited, indicating that motor control depends on precise neural pathways rather than general brain activity. Later research also found that stimulation of the same cortical areas could trigger movement, further confirming their motor role.
SOMATOSENSORY CORTEX: Ablations or lesions in the somatosensory cortex caused animals to lose awareness of touch, temperature, and body position. Because animals cannot verbally describe sensations, researchers inferred these losses from behaviour—such as failing to withdraw from heat, ignoring tactile stimuli, or showing uncoordinated limb use. The findings demonstrated that the somatosensory cortex receives and interprets information from the body in an organised, mapped pattern, with neighbouring cortical regions representing adjacent body areas.
VISUAL CORTEX: Lesions in the visual cortex resulted in blindness or specific visual deficits, depending on the site of damage. Removal of the entire visual cortex resulted in complete blindness, whereas partial lesions led to loss of specific visual field regions. These studies confirmed that the occipital lobe is essential for processing visual input, with different subregions specialising in features such as shape, orientation, and movement. This helped establish that vision is not a single function but a complex process distributed across multiple visual areas.
NON INVASIVE METHODS OF INVESTIGATING THE BRAIN: COGNITIVE NEUROSCIENCE SCANNING TECHNIQUES
Modern case studies often include neuroimaging, such as fMRI, PET, or CT, to assess brain activity and structure. These tools allow researchers to observe which brain regions are active during specific tasks or to visualise damage after injury. This approach maintains the idiographic focus of case studies while incorporating objective, measurable data.
ELECTRICAL STIMULATION OF ANIMALS
TIME PERIOD:
1870s – Present (refined)
PURPOSE:
To determine which areas of the brain control specific movements or sensations by directly stimulating the cortex with weak electrical currents.
Electrical stimulation was a breakthrough in mapping brain function, enabling researchers to observe the effects of activating specific cortical areas in real time. By applying small electrical currents to the exposed brain during surgery or in controlled animal experiments, scientists could determine which movements, sensations, or perceptions were elicited. Stimulating the motor cortex over specific body parts confirmed its role in voluntary control. Stimulation of the somatosensory cortex elicited sensations such as tingling or pressure in the corresponding body regions, thereby demonstrating its somatotopic organisation. When the visual cortex was stimulated, patients or animals reported flashes of light known as phosphenes, confirming its role in visual processing. Unlike ablations and lesions, this technique revealed function without destroying tissue, providing direct evidence for localisation and cortical organisation.
CONTEXT AND USE:
As physiological techniques improved in the late 19th century, electrical stimulation enabled researchers to observe the brain in action rather than relying solely on damage or post-mortem evidence. Small electrodes were placed on the exposed cortex of anaesthetised animals, and the resulting body movements or sensory responses were carefully recorded.
WHAT IT SHOWED:
This research demonstrated that stimulating one region of the neocortex produced a specific movement in the contralateral body part, whereas stimulating adjacent areas elicited related movements or sensations. It revealed that the cortex is functionally organised in an ordered and predictable way, leading to the identification of motor and sensory maps (known as homunculi).
WHY IT CONTINUED:
Electrical stimulation provided a reversible, controlled method for studying brain function without removing tissue or causing lasting damage. It provided the first experimental evidence of functional organisation in the cortex and remains useful in animal research today, with modern refinements enabling exact stimulation of individual neurons or circuits.
EEG (ELECTROENCEPHALOGRAPHY)
Time period: 1920s – Present
Purpose: To record the brain’s electrical activity through electrodes placed on the scalp.
Context and use: The first non-invasive method for studying the living human brain. Measures voltage changes to detect brain waves and timing of neural responses.
What it showed: Revealed that brain activity changes during sleep, sensory input, and voluntary movement. It provided early evidence that specific wave patterns are linked to different states of arousal and cognitive processing.
Why it continues to be used: EEG remains widely used for its excellent temporal accuracy and safety, although its spatial precision is limited relative to modern imaging modalities.
PSYCHOSURGERY AND NEUROSURGICAL PROCEDURES
PURPOSE: To treat severe psychiatric or behavioural disorders by altering brain connections.
TIME PERIOD:: 1930s – 1970s
Context and use: Introduced when few psychiatric treatments existed. Procedures such as frontal lobotomies and amygdalectomies aimed to reduce aggression, anxiety, or obsessive behaviour.
From the 1930s onwards, psychosurgery and neurosurgery provided some of the most unmistakable early evidence for localisation of brain function. These operations, often experimental by modern standards, allowed researchers to observe live brain activity and its immediate effects on behaviour, emotion, and cognition. Over time, techniques became more refined, moving from crude lesioning to precise electrical stimulation and cortical mapping.
1930s–1950s: FRONTAL LOBOTOMIES
In the 1930s, António Egas Moniz developed the frontal lobotomy to treat severe psychiatric illnesses such as schizophrenia and depression. The procedure involved cutting connections between the frontal lobes and deeper limbic structures. Patients often became calmer and less agitated, but many lost motivation, initiative, and emotional depth. These effects demonstrated the frontal lobes’ role in planning, personality, and emotional regulation.
1940s–1960s: AMYGDALA AND EMOTION (AMYGDALECTOMIES)
By the 1940s, neurosurgeons began removing or disconnecting the amygdala in patients with extreme aggression or anxiety. Following surgery, many showed a striking reduction in aggressive behaviour and fear responses, confirming the amygdala’s role in processing emotion and threat. Similar findings were later replicated in animal studies.
1953: HIPPOCAMPUS AND MEMORY (PATIENT H.M.)
In 1953, Henry Molaison (H.M.) underwent bilateral removal of the hippocampus to control epilepsy. The operation stopped his seizures but left him unable to form new long-term memories. This case revealed the hippocampus as essential for memory consolidation — the process of transferring information from short-term to long-term storage — and profoundly shaped understanding of memory systems.
WHAT IS SHOWED: Linked the frontal lobes and limbic system to emotional regulation, decision-making, and personality. It demonstrated localisation of these higher-order functions but also exposed the dangers of interfering with them.
WHY IT DECLINED: Effects were often unpredictable and irreversible, leaving patients apathetic or cognitively impaired. The rise of psychiatric medication and stricter ethical standards made psychosurgery largely obsolete. Many early findings on localisation of function, including the work of Broca and Wernicke, came from post-mortem examinations. While these have been instrumental in identifying brain regions associated with specific functions, several significant drawbacks remain. Post-mortem studies cannot capture real-time brain activity, making it impossible to observe how the brain functions during cognitive tasks. Furthermore, because they are conducted postmortem, there is no opportunity to measure plasticity or to assess how other brain areas compensate for damage. Additionally, individual differences such as bilingualism—which can lead to different development in Broca’s area—cannot be accounted for, making it difficult to generalise findings to the broader population.
NEUROSURGICAL PROCEDURES/ ELECTRICAL STIMULATION AND BLOCKING IN HUMANS (INTRAOPERATIVE MAPPING)
Time period: 1930s – Present
Purpose: To locate critical cortical areas during brain surgery and prevent accidental damage to speech, movement, or sensory regions.
CONTEXT AND USE: Developed in neurosurgery, particularly for patients with epilepsy or brain tumours. During awake operations, small electrical pulses are applied to exposed cortical areas while the patient performs tasks or responds verbally.
1950s–1970s: INTRAOPERATIVE ELECTRICAL STIMULATION
From the 1950s onwards, surgeons such as Wilder Penfield performed awake brain surgeries for epilepsy and tumours using local anaesthetics. Small electrical currents were applied to exposed cortical tissue to assess its function prior to removal. Stimulation of the motor cortex moved to specific body parts; stimulation of the somatosensory cortex caused tingling or touch sensations; and stimulation of the visual cortex produced flashes of light (phosphenes). This technique provided direct, real-time evidence for localisation of motor, sensory, and visual function and is still used today to avoid damaging critical areas.
1960s: BROCA’S AREA AND LANGUAGE LOCALISATION
Electrical stimulation or temporary inhibition of tissue near Broca’s area during awake surgery caused patients to pause or lose speech mid-sentence. This confirmed that the left inferior frontal gyrus is essential for speech production and allowed surgeons to operate safely around language centres.
1960s–PRESENT: TEMPORARY BLOCKING AND CORTICAL INHIBITION
Electrical or cooling probes were used temporarily to block neural activity during awake surgery. When an area was inhibited, the corresponding function—such as speech, movement, or sensation—ceased immediately. This reversible technique allowed surgeons to identify functional boundaries precisely and remains standard practice in neurosurgery today.
1960s–1970s: COMMISSUROTOMIES (SPLIT-BRAIN SURGERY)
In the 1960s and 1970s, surgeons treated severe epilepsy by cutting the corpus callosum, the bundle connecting the two hemispheres. Research by Roger Sperry and Michael Gazzaniga on these “split-brain” patients revealed that the left hemisphere specialises in language and analytical thought. In contrast, the right hemisphere is dominant for spatial awareness and visual processing. These findings provided some of the most substantial evidence for hemispheric lateralisation.
WHAT WAS LEARNED
These decades of surgical investigation established several key principles:
The frontal lobes regulate emotion, planning, and personality.
The amygdala mediates aggression and fear.
The hippocampus is essential for memory formation.
The left hemisphere specialises in language.
The corpus callosum integrates information between hemispheres.
What it showed: Stimulation of the motor cortex moves; stimulation of the sensory cortex causes tingling or pressure; stimulation of the visual cortex produces flashes of light (phosphenes). Temporary blocking near Broca’s area can stop speech mid-sentence. This gave direct evidence of localisation in living humans.
Why it continues: Still used in modern neurosurgery, it remains one of the few methods that provides causal evidence of brain function in awake patients.
NEUROTOXINS
Time period: 1950s – Present (mainly animal research)
Purpose: To deactivate or destroy selected groups of neurons using targeted chemicals.
Context and use: Developed to study the function of specific neural systems more precisely than surgical lesions.
What it showed: Allowed researchers to study the effects of removing single neurotransmitter systems or small neural populations, helping to isolate fine control mechanisms in movement and emotion.
Why its use is limited: Mostly restricted to animal studies due to ethical and safety concerns in humans; newer non-invasive techniques can now study similar processes without cell destruction.
MODERN SCANNING AND COGNITIVE NEUROSCIENCE
TIME PERIOD:
1970s – Present
PURPOSE:
To investigate both the structure and function of the living brain using non-invasive techniques that allow repeated, precise, and ethical observation.
CONTEXT AND USE:
From the 1970s onwards, new imaging technologies transformed localisation research. CT and MRI scans revealed detailed brain structures, while PET and later fMRI allowed researchers to observe brain activity in real time. By the 1990s, these tools had evolved into the field of cognitive neuroscience—the study of how cognitive processes such as language, memory, and perception are represented in neural systems. Researchers began integrating imaging data with electrophysiological measures (EEG and MEG), lesion evidence, and computer modelling to understand how networks of cortical areas work together.
WHAT IT SHOWED:
Modern imaging confirmed and extended earlier findings from post-mortem and lesion studies, demonstrating that complex behaviours arise from interactions among multiple specialised regions rather than from isolated centres. fMRI, in particular, enabled dynamic mapping of brain activity, revealing how different cortical areas communicate during sensory, motor, and higher-order cognitive tasks.
WHY IT DOMINATES TODAY:
Modern scanning and cognitive neuroscience together represent the most advanced and ethical approach to studying the human brain. They combine anatomical precision with functional measurement, allowing both structure and activity to be studied in the same individuals. This integration has replaced invasive historical methods and continues to refine our understanding of localisation and brain connectivity.
In recent research, methods such as fMRI, PET, and EEG have revolutionised our understanding of functional localisation by enabling real-time observation of brain activity without invasive procedures. However, even these methods have limitations. For instance, fMRI can show which brain areas are active during specific tasks. Still, it cannot establish causality—simply because a region is active doesn't mean it is solely responsible for the behaviour under study. Neuroimaging often reveals distributed neural activity, indicating that multiple areas are involved in even simple tasks. This challenges strict localisation theories, which suggest that each brain function is housed in a specific location.
