Localisation of function in the brain

Localisation versus holistic theory

Broca and Wernicke discovered that specific areas of the brain are associated with particular physical and psychological functions

Before these investigations scientists generally supported the holistic theory of the brain- that all parts of the brain were involved in the processing of thought and action

In contrast, Broca and Wernicke argued for localisation of function- the idea that different parts of the brain perform different tasks and are involved with different parts of the body

So if a certain area of the brain becomes damaged through illness or injury the function associated with that area will also be affected

Hemispheres of the brain

Main part of the brain (cerebrum) is divided into symmetrical halves called the left and right hemispheres

Some of our physical and psychological functions are controlled by a particular hemisphere- this is called lateralisation

Activity on the left hand side of the body is controlled by the right hemisphere and activity on the right hand side is controlled by the left hemisphere

Language is linked to the left hemisphere

Cerebral cortex

Outer layer of both hemispheres

It covers the inner parts of the brain

The cortex appears grey due to the location of cell bodies

Cortex of both hemispheres is subdivided into four centres- called the lobes of the brain: the frontal lobe, the parietal lobe, the occipital lobe and the temporal lobe

A lobe is a part of an organ that is separate in some way from the rest- each lobe is associated with different functions

Frontal lobe

At the back of the frontal lobes in both hemispheres is the motor centre which controls voluntary movement in the opposite side of the body

Damage to this area of the brain may result in a loss of control over fine movements

Parietal lobes

At the front of both parietal lobes is the somatosensory centre which is separated from the motor centre by a valley called the central sulcus

The somatosensory centre is where sensory information from the skin (related to touch, heat and pressure) is represented

The amount of somatosensory area devoted to a particular body part denotes its sensitivity, for instance, receptors for our face and hands occupy over half of the somatosensory centre

Occipital lobes

In the occipital lobes at the back of the brain is the visual centre

Each eye sends information from the right visual field to the left visual cortex and from the left visual field to the right visual cortex

This means that damage to the left hemisphere, can produce blindness in part of the right visual field of both eyes

Temporal lobes

House the auditory centre, which analyses speech based information

Damage may produce partial hearing loss

The more extensive the damage, the more extensive the loss

In addition, damage to a specific area of the left temporal lobe- wernickes area- may affect the ability to comprehend language

Language centres of the brain

Language is restricted to the left side of the brain in most people

Broca, a surgeon, identified a small area in the left frontal lobe responsible for speech production

Damage to Broca’s area causes Broca’s aphasia which is characterised by speech that is slow and lacking in frequency

Broca’s most famous patient was tan - called that because that was the only word he could say

People with Broca’s aphasia often have stilted speech

Wernickes area

Wernicke was describing people who had no problem producing language but severe difficulties understanding it, which meant that the speech they produced was effortless but meaningless

Wernicke identified a region (wernickes area) in the left temporal lobe as being responsible for language understanding

This results in wernickes aphasia when damaged- people with this will often produce language but have problems understanding it, so they produce nonsense words as part of the content of their speech