BP - Localisation Theory -The Brain

Question 1

What is localisation theory?

Answer 1

• This is the theory that different areas of the brain are responsible for different behaviours, cognitive processes o activities and are associated with different parts of the body - often called cortical specialisation
• Before the introduction of this theory, scientists generally supported the holistic theory of the brain - that all parts of the brain are involved in the processing of thought and emotion

Question 2

What does it involve?

Answer 2

It involves restricted areas of the cortex e.g. motor cortex controls voluntary movement, or broader aspects e.g. right hemisphere being responsible for visual-spatial functions.

• Some functions are more localised than others, whilst other functions are more widely distributed
• Example of localised - movement is highly localised to the motor cortex
• Example of distributed - language system

Based on this theory, it is thought that if a certain area of the brain is damaged through illness or injury, the function associated with it will also be affected.

Question 3

The cerebral cortex

Answer 3

• The brain is divided into two symmetrical halves, called hemispheres (left and right)
• Some functions are dominated by one hemisphere - this is called lateralisation
• Activity on the left side of the body is controlled by the right hemisphere, and vice versa
• The outer layer of both hemispheres is called the cerebral cortex, with each hemisphere being made up of four lobes, or sections
• Within each lobe there are distinct areas that are thought to have different specific functions according to localisation theory

Question 4

The motor cortex

Answer 4

• Responsible for the generation of voluntary motor movements - it is located in the frontal lobe, along with the region known as the precentral gyrus
• This is a region located just in front of the central sulcus, that divides the frontal and parietal lobes; both hemispheres of the brain have a motor cortex
  1. The cortex on one side controls the muscles and movement on the opposite side, with different parts of the whole cortex controlling different body parts
• These parts are logically arranged next to one another
• Damage to this area may result in loss of control over fine motor movements

Question 5

The auditory centres

Answer 5

• Concerned with the analysis of speech based information i.e. hearing
• Most of this area resides in the temporal lobes on both sides of the brain where we find the auditory cortex
• Auditory pathway begins in the cochlea in the inner ear, where sound waves are converted to action potentials, which travel via the auditory nerve to the auditory cortex in the brain
• Damage may produce partial hearing loss - more extensive damage = more extensive loss

Question 6

The somatosensory cortex

Answer 6

• The part of the brain that processes input from sensory receptors in the body that are sensitive to touch
• it is located in the parietal lobe, along a region known as the postcentral gyrus; a region just behind the central sulcus that divides the frontal and parietal lobe
• Using sensory information from the skin, the somatosensory cortex produces sensations of touch, pressure, pain and temperature, which it then localises to specific body regions
• Both hemispheres have this cortex, with the cortex on one side processing and receiving sensory information from the opposite side etc
• The amount of somatosensory area devoted to a particular body part denotes its sensitivity e.g. receptors on the face and hands occupy over half of the somatosensory cortex, often represented in the form of a homunculus

Question 7

The visual centres

Answer 7

• Primary visual centre is located in the visual cortex in the occipital lobe; it is in the part of the occipital lobe that receives and processes visual information
• Visual processing begins in the retina, at the back of the eye, where light enters and strikes photoreceptors called rods and cones
• Action potentials from the retina are then transmitted to the brain via the optic nerve and most of the action potentials terminate in the thalamus, which acts as a relay station, passing the information to the visual cortex
• The visual cortex spans both hemispheres, with the right hemisphere receiving its input from the left hand side of the visual field, and the left hemisphere receiving information from the right side of your visual field
• The visual cortex contains several different areas, with each of these areas processing different types of visual information such as colour, shape or movement

Question 8

Broca’s Area

Answer 8

• Systematic research from Wernicke and Broca have shown that language centres are lateralized to the left hemisphere - Broca’s area concerns production of speech
• Paul Broca is the namesake of this area, after he treated a patient known as ‘Tan’ because that was the only syllable he could express - Tan could understand spoken language, but could neither speak or express his thoughts in writing
• Broca then studied other patients who had similar language deficits and those with lesions along their left frontal hemisphere
• He found that patients with damage to these areas in the right hemisphere did not have the same language problems, leading to him identifying a language centre in the posterior portion of the left frontal lobe, an area believed to be critical for speech production
• People with damage to Broca’s area - Broca’s aphasia - are often only able to talk on short, meaningful sentences which take great effort (slow and laborious), with their speech lacking fluency as there is difficulty with words that help sentences to function (e.g. it)

Question 9

Wernicke’s Area

Answer 9

• Carl Wernicke discovered an area of the brain involved with understanding language; Wernicke’s area
• This is located in the posterior portion of the left temporal lobe that encircled the auditory cortex
• Wernicke found that patients with a lesion to this area - Wernicke’s aphasia - could speak but were unable to understand and interpret speech and language, meaning their speech was fluent but meaningless
• They often produce nonsense words, or neologisms, as part of their speech content
• Wernicke proposed that language involves separate motor and and sensory regions located in different regions of the brain - the sensory region is in Wernicke’s area, and is close to the region of auditory and visual output
• Input from these regions is transferred to WA where it is recognised as language and associated with a meaning
• The motor region is located in Broca’s area, and is close to the region that controls the mouth, tongue and vocal cords
• There is a neural loop running between Wernicke’s and Broca’s areas

Question 10

Summary of localisation

Answer 10

• There are specific areas of the brain that are localised
• Some functions are more localised than others (motor cortex), and some are more widely distributed (language centres)
• Localisation can involve restricted areas of the cortex

Question 11

Evaluation of localisation theory - supporting evidence

Answer 11

• Phineas Gage - damage to frontal lobe following injury changed his personality to quick-tempered and rude from calm and reserved, suggesting that the frontal lobe regulates mood and supporting localisation; however, as it is a case study, it cannot provide strong support through a lack of external validity and the possibility of Gage being a unique case
• Studies of people with Broca’s aphasia have found an impaired production of language, and those with Wernicke’s aphasia have been found to have impaired understanding of language; this supports the importance of Broca’s area in speech production (motor region) and Wernicke’s area in language comprehension (sensory region) and so they support the idea of some components of the language system being localised
• Peterson et al used brain scans to demonstrate how Wernicke’s area was active during a reading task, and Tulving et al studied LTM and found that episodic and semantic memory reside in different parts of the prefrontal cortex; these studies suggest that different brain areas have different functions, supporting localisation theory - there are now many objective and highly sophisticated methods of measuring brain activity which provide sound scientific evidence of localisation of brain function

Question 12

Evaluation of localisation theory - undermining evidence

Answer 12

• Lashley removed 10-50% of the areas in a rat’s cortex whilst they were learning a maze, with no area proving to be more important in terms of the rat’s ability to learn the maze; suggests learning processes require every section of the cortex, suggesting it is too complex to be localised and so similar processes and learning may be more holistically distributed; however, should be cautious in drawing conclusions related to animal studies and so their learning process and brain localisation may be different to humans
• When the brain is damaged, and a particular function is compromised or lost, the rest of the brain is able to reorganise itself to recover the lost function (plasticity) and although this does not happen every time, there are documented cases of stroke victims recovering those abilities that were lost; suggests functioning may be more holistic as other brain areas were able to recover the function of a particular damaged area
• A French neurologist found the loss of his ability to read resulted from damage to the connection between the visual cortex and Wernicke’s area; suggests how brain areas communicate with one another may be more important than what specific region controls a specific cognitive process - Wernicke claimed that although different brain regions had different functions, they are interdependent (must interact to function) and damage to the connection between any two points in the process results in impairments that resemble damage to the localised brain region associated with a particular function

Question 13

Burt B’s Brain Structure

Answer 13

Frontal Lobe - Red, Front of brain 
Parietal Lobe - Purple, Top of brain
Occipital Lobe - Blue, Back of brain
Temporal Lobe - Green, Base of brain
Brain stem - primitive part of the brain, connecting it and the spinal cord (orange) 

• Wernicke’s Area = top of temporal lobe, near base of parietal lobe (understand language)
• Broca’s Area (produce language) = Back of frontal lobe
• Motor Cortex = across parietal lobe, stretching from back of frontal across both hemispheres (upwards)
• Somatosensory Cortex = Parietal lobe, to left of motor cortex
• Corpus Callosum - nerve fibre between hemispheres that allows hemispherical communication