4. Localisation of function in the brain

What is Localisation?

the theory that specific areas of the brain are associated with particular physical and psychological functions.

(If an areas of the brain is damaged through illness or injury, the function associated with that area is also affected)

What is Lateralisation?

The dominance of one hemisphere of the brain for particular physical and psychological functions.

(Brocas and Wernickes ares, that are only found in the LH)

5 areas of brain that are localised?

• Visual cortex

• Auditory cortex

• Motor cortex

• Somatosensory cortex

• Language areas (Brocas and Wernickes)

Motor cortex

Location: at the back of the frontal lobe, in both LH and RH

Function: controls voluntary movement and regulates mood (left side of the body is controlled by right frontal lobe and vice versa)

Damage: loss of movement, paralysis (if damage RH, loss of movement in the left side of the body and vice versa), damage to specifically Left frontal lobe→ Brocas aphasia (difficulty with speech production)

Somatosensory cortex

Location: at the front of the parietal lobe, separated from the motor area by the central sulcus

Functions: processes sensory info from the skin(touch, heat, pressure

Additional: the amount of somatosensory ares devoted to a body part reflects its sensitivity. Hands and face occupy a large proportion because they contain many sensory receptors.

Visual cortex

Location: occipital lobe

Functions: processes visual info (each eye sends info from the RVF to the left visual cortex and vice versa)

Damage: damage to the LH can produce blindness in part of the RVF in both eyes

Auditory cortex

Location: temporal lobe

Functions: analyses speech-based info

Damage: may produce partial hearing loss( depends how extensive the damage is), damage to the left temporal lobe causes Wernickes aphasia (fluent, but nonsense speech)

Broca’s area (language area)

Location: localised to the Left frontal lobe, therefore lateralised (only left frontal lobe is responsible for this function)

Functions: responsible for speech production and enables speech to be fluent

Damage: damage to the Left frontal lobe can lead to Brocas aphasia (slow speech, difficulty with producing speech, especially with connecting words “it” and “the”)

Wernicke’s area (language area)

Location: localised to the left temporal lobe, therefore lateralised (only left temporal lobe responsible for this function)

Functions: responsible for language comprehension and enables speech to be meaningful

Damage: damage leads to Wernickes aphasia (people produce nonsensical speech and nonsense words)

Evaluations (Localisation of function in the brain)

Support from case study

Ev: The case of Phineas Gage showed that damage to the frontal lobe changed his personality from calm to someone who was rude and aggressive. Ex: shows that certain functions can be localised to particular areas of the brain. Damage to frontal lobe showed changes in personality, suggests that personality and behaviour are associated with specific areas of the brain, particularly the frontal lobe. L: High internal validity, as supports the idea that specific functions are localised to particular brain areas.

Cognitive functions are distributed more holistically across the brain

Ev: Research has removed between 10% and 50% of the prefrontal cortex in rats that were learning route through maze. No area was shown to be more important in terms of the rats LTM ability to learn the route. Ex: suggests that memory may not be localised to one specific brain area and instead may involve several regions working together. L: questions internal validity, as functions may not be controlled by a single localised area.

Contradictory research

Ev: Research scanned the brain of Brocas patients with MRI scanning. He found that other areas of the brain could have also contributed to the patients reduced speech abilities. Ex: Suggests that language production may involve several interconnected brain regions, rather than just Broca’s area. Damage to one area doesn’t always produce the same symptoms in every patient. L: low reliability, as findings don’t consistently show that one specific brain area is solely responsible for a particular function