AQA Syllabus focus:
'Localisation of function in the brain and hemispheric lateralisation, including motor, somatosensory, visual, auditory and language centres.'
These notes explain how specific brain areas are linked to specific functions and how the left and right hemispheres show different specializations while still working together as one system.
Localization of Function in the Brain
Localization of function means that particular areas of the brain are specialized for particular activities rather than all areas doing the same job.
Localization of function: The idea that specific psychological or physical functions are controlled by particular areas of the brain.
One reason psychologists support localization is that damage to one brain area can produce a specific loss of function. Much of this specialization is found in the cerebral cortex, the folded outer layer of the brain involved in higher mental processes. Although the cortex works as a connected whole, some regions have especially important roles.
This Brodmann-area map illustrates how the cerebral cortex can be subdivided into distinct regions with characteristic locations and functional associations. It helps you visualize that “localization” is not just about lobes, but about smaller cortical zones that can be linked to motor, sensory, and language-related processing. Source
Motor Cortex
The motor cortex is located at the back of the frontal lobe in both hemispheres. It is responsible for voluntary movement.
The left motor cortex controls movement on the right side of the body.
The right motor cortex controls movement on the left side of the body.
Different areas of the motor cortex control different body parts, such as the face, hands, and legs.
A larger cortical area is devoted to body parts needing fine control, especially the hands and face. Damage to the motor cortex can lead to loss of movement, weakness, or difficulty coordinating precise actions.
Somatosensory Cortex
The somatosensory cortex is located at the front of the parietal lobe, directly behind the motor cortex. It processes sensory information from the skin and body.
touch
pressure
pain
temperature
body position
Like the motor cortex, it is arranged so that each hemisphere mainly receives information from the opposite side of the body. More sensitive body areas, such as the lips and fingertips, are given more cortical space.
The cortical homunculus diagram(s) show the somatotopic map of the body across the motor and/or somatosensory cortex, where body parts are drawn larger when they occupy more cortical area. This provides a visual explanation for why the hands, lips, and face have disproportionately large representations compared with the trunk or legs. Source
Damage can cause numbness, reduced sensitivity, or problems identifying where sensations are coming from.
Visual Cortex
The visual cortex is found in the occipital lobe at the back of the brain. Its main function is processing visual input.
Information from the eyes is split so that the left hemisphere processes the right visual field and the right hemisphere processes the left visual field. The cortex interprets shape, color, movement, and pattern, allowing visual perception. Damage to the visual cortex can cause partial or total loss of vision, even when the eyes themselves are healthy.
Auditory Cortex
The auditory cortex is located in the temporal lobe and is involved in analyzing sound.
It helps the brain identify:
pitch
loudness
rhythm
meaning in speech sounds
Unlike some other sensory systems, auditory information is sent to both hemispheres, although each hemisphere may specialize slightly in different aspects of sound processing. Damage can lead to difficulties interpreting sounds.
Language Centers
Language is one of the clearest examples of localization. In most people, especially right-handed individuals, language functions are mainly located in the left hemisphere.
Two important language areas are:
This diagram highlights the approximate positions of Broca’s area (speech production) and Wernicke’s area (language comprehension) on a lateral view of the brain. It is useful for linking different patterns of aphasia to damage in different language regions, supporting the localization argument in the notes. Source
Broca's area, in the left frontal lobe, linked with speech production
Wernicke's area, in the left temporal lobe, linked with language comprehension
Damage to Broca's area is associated with slow, effortful speech, whereas damage to Wernicke's area is associated with fluent but often meaningless speech and poor understanding. These patterns show that different aspects of language are localized in different brain regions.
Hemispheric Lateralization
Hemispheric lateralization refers to the idea that the two hemispheres of the brain are functionally different, with some processes being more dominant in one hemisphere than the other.
Hemispheric lateralization: The specialization of the left and right hemispheres for different psychological functions.
This does not mean each hemisphere works independently. Most everyday behavior involves both hemispheres, but one side may play a greater role in a particular task. The hemispheres also show contralateral control, meaning each side of the brain mainly controls or receives information from the opposite side of the body.
The left hemisphere is usually more involved in:
language
speech
logical analysis
fine detail
The right hemisphere is usually more involved in:
spatial awareness
face recognition
some musical and nonverbal processing
holistic pattern processing
Language lateralization is especially important because it links localization with hemispheric differences. Broca's and Wernicke's areas are usually found in the left hemisphere, showing that some specialized functions are not only localized but also lateralized.
However, lateralization is not absolute. Some left-handed people show more right-hemisphere or mixed language dominance, and many cognitive activities use both hemispheres together. This means specialization increases efficiency, but brain functioning remains highly interconnected.
Linking Localization and Lateralization
Understanding these ideas helps psychologists explain why particular brain injuries cause particular difficulties. For example:
damage to the motor cortex may affect voluntary movement
damage to the somatosensory cortex may disrupt bodily sensation
damage to the visual cortex may impair sight
damage to the auditory cortex may affect sound processing
damage to language areas may cause speech or comprehension difficulties
These links between area and function support the view that the brain has specialized regions, while hemispheric lateralization shows that specialization can also occur between the left and right sides of the brain.
Practice Questions
Briefly outline what is meant by hemispheric lateralization. (2 marks)
1 mark for stating that the left and right hemispheres are specialized for different functions.
1 mark for a relevant example, such as language usually being more dominant in the left hemisphere.
Explain localization of function in the brain. Refer to at least three cortical areas in your answer. (6 marks)
1 mark for explaining that localization means specific functions are controlled by specific brain areas.
1 mark for identifying the motor cortex as responsible for voluntary movement.
1 mark for identifying the somatosensory cortex as responsible for processing sensory information from the body.
1 mark for identifying the visual cortex as responsible for visual processing.
1 mark for identifying the auditory cortex as responsible for sound processing.
1 mark for identifying language centers, such as Broca's area for speech production or Wernicke's area for language comprehension.
FAQ
These body parts need especially precise control and produce especially detailed sensory input, so the brain gives them more cortical area.
This does not mean the hands and face are physically bigger. It means they are more important for:
fine movement
detailed touch
rapid feedback to the brain
A cortical homunculus is a visual map showing how body parts are represented on the motor or somatosensory cortex.
It looks distorted because body parts with greater sensitivity or finer movement control appear much larger than less sensitive areas. For example, the lips, tongue, and hands are shown as very large compared with the trunk or legs.
Yes. Although many left-handed people still show left-hemisphere language dominance, there is more variation than in right-handed people.
Some left-handed individuals show:
right-hemisphere language dominance
more even distribution across both hemispheres
This is one reason psychologists avoid saying that language is always located in exactly the same place for every person.
The idea is misleading because hemispheric lateralization applies to some functions, not to whole personality types.
In reality:
most tasks use both hemispheres
the brain works through connected networks
people are not simply “logical left-brained” or “creative right-brained”
The theory of lateralization is about functional specialization, not personality labels.
The effects of brain damage depend on more than just the named area. Small differences in lesion size, exact location, and the person's existing brain organization can change the outcome.
Other factors include:
handedness
age
overall health
which nearby networks are also affected
So two people with damage in the same lobe may not show identical problems.
