localisation of function

The human brain is a complex biological system, with different functions localised in specific areas.
Key brain regions include:
- Motor area
- Somatosensory area
- Visual area
- Auditory area
- Broca's area
- Wernicke's area

Localisation of Function: The theory that specific areas of the brain are responsible for distinct behaviours, processes, or activities.
Motor Area: A region of the frontal lobe involved in regulating voluntary movement.
Somatosensory Area: Located in the parietal lobe, processes sensory information such as touch, heat, and pressure.
Visual Area: Found in the occipital lobe; this area receives and processes visual information.
Auditory Area: Situated in the temporal lobe, concerned with speech-based information analysis.
Broca's Area: In the left hemisphere of the frontal lobe, responsible for speech production.
Wernicke's Area: In the left hemisphere of the temporal lobe, responsible for language comprehension.

The cerebrum, the main part of the brain, is divided into two hemispheres: left and right.
Each hemisphere controls functions related to the opposite side of the body - known as lateralisation.
The left hemisphere is typically linked to language functions.

Historically, the holistic theory suggested all parts of the brain work together for thought processing.
Pioneers like Paul Broca and Karl Wernicke demonstrated that specific brain areas are linked to particular functions, leading to the concept of localisation of function or cortical specialisation.
Damage to specific brain areas results in loss of function associated with that area due to the role of each region in performing distinct tasks.

Each hemisphere has symmetrical halves that control different physical and psychological functions.
- The left hemisphere is typically responsible for language.
- The right hemisphere controls activities on the opposite side of the body.

The cerebral cortex is divided into four lobes:
1. Frontal Lobe: Contains the motor area, involved in voluntary movement.
2. Parietal Lobe: Houses the somatosensory area, processing sensory information.
3. Occipital Lobe: Home to the visual area, processing visual stimuli.
4. Temporal Lobe: Contains the auditory area for processing sound and speech.

Located at the front of both parietal lobes.
Separated from the motor area by the central sulcus.
Represents sensory information from the skin; sensitivity is proportionate to the area dedicated to the body part.
- Example: The face and hands occupy a significantly larger portion of the somatosensory area, reflecting their higher sensitivity.

Located in the occipital lobe at the brain's back.
Each eye transmits information from the right visual field to the left visual cortex, and vice versa.
Damage to the left hemisphere can cause blindness in part of the right visual field.

Located within the temporal lobes.
Analyzes speech-based information and is crucial for processing sounds.
Damage can lead to partial hearing loss; severity of damage correlates to the extent of hearing loss.

Language is predominantly localised in the left hemisphere for most individuals.

Discovered by Paul Broca in the 1880s within the left frontal lobe.
Responsible for speech production; damage results in Broca's aphasia, characterized by slow and laborious speech, often lacking fluency.
- Example: Broca's patient "Tan", could only say his name, highlighting the functional impairment.

Identified by Karl Wernicke, located in the left temporal lobe.
Responsible for language comprehension; damage leads to Wernicke's aphasia, where individuals can produce fluent but meaningless speech, often incorporating neologisms.

Strengths:
- Evidence from Neurosurgery: Treatments targeting specific brain areas link damage to mental disorders. For example, cingulotomy isolates a gyrus implicated in OCD.
- Study by Dougherty et al. (2002): 44 OCD patients post-surgery showed 30% met criteria for response, affirming behaviour localisation.
- Neuroimaging Studies: Research using brain scans shows localisation in brain functions, e.g., Petersen et al. (1988) found Broca's area active during reading.
- Buckner and Petersen (1996): Semantic and episodic memories are located in different parts of the prefrontal cortex.
Counterpoints:
- Karl Lashley's study (1950) on rats showed that learning required the entire cortex, challenging the idea of function being confined to specific areas, suggesting a more holistic approach.

Advances in research indicate language functions are more distributed across the brain than previously thought.
- Only 2% of modern researchers believe language is confined to Broca's and Wernicke's areas (Dick & Tremblay, 2016).
- Recent fMRI studies reveal language streams distributed across the cortex, including the right hemisphere and subcortical regions like the thalamus.

Phineas Gage (1848) exemplifies localisation theory; following a significant brain injury, his personality drastically changed, suggesting the frontal lobe regulates mood.
- Case studies highlight potential issues of generalisation and subjective interpretation of findings.
- Critical Questions: How does reliance on individual cases impact the validity of evidence for localisation theory?

Explain what is meant by localisation of function using an example.
Identify locations in the brain for:
- (i) Motor area
- (ii) Visual area
- (iii) Auditory area.
Describe the roles of Broca's and Wernicke's areas in language localisation.
Discuss research that demonstrates localisation of function in the brain.