LOCALISATION OF FUNCTION IN THE BRAIN
DESCRIPTION (AO1)
Localisation Theory:
Localisation of function is the idea that different parts of the brain are responsible for different
specialised functions. Damage to a certain area of the brain through illness or injury would affect
the function associated with that area.
Brain is divided into two hemispheres and is lateralised:
LATERALISATION – some of our physical and psychological functions are controlled by a particular
hemisphere.
CONTRALATERAL – each hemisphere deals with information from the opposite side of the body.
E.g. activity of the left side of the body is controlled by the right hemisphere and vice versa.
Outer layer of brain is called the Cerebral Cortex:
It is 3mm thick and is what separates us from lower animals as it’s highly developed.
The cortex appears grey due to location of cell bodies.
Sub-division of the hemispheres into four lobes (frontal, parietal, occipital, temporal):
MOTOR AREA – in the back of the frontal lobe and controls voluntary movement by
producing movement of muscle fibres. This function is specialised laterally, with
the left hemisphere controlling the right side of the body.
SOMATOSENSORY AREA – in the front of the parietal lobe and is responsible for
detecting and processing sensory info from receptors in the skin (touch, heat).
VISUAL CORTEX – in the occipital area at the back of the brain. Each eye sends info
from right visual field to left visual cortex and vice versa.
AUDITORY CORTEX – in the temporal lobe and analyses speech based information.
The Language Centres – both located in the left hemisphere:
BROCA’S AREA – SPEECH PRODUCTION
Broca used post-mortem examinations to identify that Broca’s aphasia- the
ability to understand language but the inability to produce it – was associated
with damage to the left frontal lobe.
It was then concluded that the Broca’s area is responsible for speech production.
Broca’s area is located in the left frontal lobe.
WERNICKE’S AREA – LANGUAGE UNDERSTANDING
Wernicke studied Wernicke’s aphasia, where nonsense speech (fluent but meaningless) is
produced, and concluded that the Wernicke’s area is responsible for language comprehension.
Wernicke’s area is located in the left temporal lobe.
, EVALUATION OF LOCALISATION OF FUNCTION IN THE BRAIN (AO3)
STRENGTHS
THERE IS BRAIN SCAN EVIDENCE TO SUPPORT THE LOCALISATION THEORY
Peterson et al. used brain scans to show activity in Wernicke’s area during a listening task and in
Broca’s area during a reading task, suggesting these areas of the brain have different functions.
Also, a study of long term memory by Tulving et al. revealed semantic and episodic memories are
located in different parts of the prefrontal cortex.
There now exists a number of sophisticated and objective methods of measuring activity in the
brain, providing scientific evidence and credibility of localisation of function.
SUPPORT FROM CASE STUDIES – GAGE
Unique cases of neurological damage support localisation theory, such as the case of Phineas Gage
who had serious brain damage in an accident.
Gage survived but the damage to his brain affected his personality – he went from being calm and
reserved to being quick-tempered, rude and ‘no longer Gage’.
The change in Gage’s temperament following the accident suggests the frontal lobe may be
responsible for regulating mood.
LIMITATIONS
CONTRADICTORY RESEARCH – LASHLEY
The work of Lashley suggests higher cognitive functions such as learning processes, aren’t localised
but distributed more holistically in the brain.
Lashley removed areas of the cortex (up to 50%) in rats learning the route through a maze.
No one area was more important than any other in terms of the rats’ ability to learn the maze.
As learning required all the cortex rather than being confined to a particular area, this shows
learning is too complex to be localised and involves the whole brain.
NEURAL PLASTICITY IS A CHALLENGE TO THE LOCALISATION THEORY
When the brain has become damaged due to illness or accident, and a function has been
compromised or lost, the rest of the brain is able to reorganise itself to recover the function.
Lashley called this the LAW OF EQUIPOTENTIALITY – what happens is that other areas of the brain
‘chip in’ so the same neurological action can be achieved.
This doesn’t happen every time but there are lots of case studies of stroke victims recovering
abilities seemingly lost as a result of the illness.
DESCRIPTION (AO1)
Localisation Theory:
Localisation of function is the idea that different parts of the brain are responsible for different
specialised functions. Damage to a certain area of the brain through illness or injury would affect
the function associated with that area.
Brain is divided into two hemispheres and is lateralised:
LATERALISATION – some of our physical and psychological functions are controlled by a particular
hemisphere.
CONTRALATERAL – each hemisphere deals with information from the opposite side of the body.
E.g. activity of the left side of the body is controlled by the right hemisphere and vice versa.
Outer layer of brain is called the Cerebral Cortex:
It is 3mm thick and is what separates us from lower animals as it’s highly developed.
The cortex appears grey due to location of cell bodies.
Sub-division of the hemispheres into four lobes (frontal, parietal, occipital, temporal):
MOTOR AREA – in the back of the frontal lobe and controls voluntary movement by
producing movement of muscle fibres. This function is specialised laterally, with
the left hemisphere controlling the right side of the body.
SOMATOSENSORY AREA – in the front of the parietal lobe and is responsible for
detecting and processing sensory info from receptors in the skin (touch, heat).
VISUAL CORTEX – in the occipital area at the back of the brain. Each eye sends info
from right visual field to left visual cortex and vice versa.
AUDITORY CORTEX – in the temporal lobe and analyses speech based information.
The Language Centres – both located in the left hemisphere:
BROCA’S AREA – SPEECH PRODUCTION
Broca used post-mortem examinations to identify that Broca’s aphasia- the
ability to understand language but the inability to produce it – was associated
with damage to the left frontal lobe.
It was then concluded that the Broca’s area is responsible for speech production.
Broca’s area is located in the left frontal lobe.
WERNICKE’S AREA – LANGUAGE UNDERSTANDING
Wernicke studied Wernicke’s aphasia, where nonsense speech (fluent but meaningless) is
produced, and concluded that the Wernicke’s area is responsible for language comprehension.
Wernicke’s area is located in the left temporal lobe.
, EVALUATION OF LOCALISATION OF FUNCTION IN THE BRAIN (AO3)
STRENGTHS
THERE IS BRAIN SCAN EVIDENCE TO SUPPORT THE LOCALISATION THEORY
Peterson et al. used brain scans to show activity in Wernicke’s area during a listening task and in
Broca’s area during a reading task, suggesting these areas of the brain have different functions.
Also, a study of long term memory by Tulving et al. revealed semantic and episodic memories are
located in different parts of the prefrontal cortex.
There now exists a number of sophisticated and objective methods of measuring activity in the
brain, providing scientific evidence and credibility of localisation of function.
SUPPORT FROM CASE STUDIES – GAGE
Unique cases of neurological damage support localisation theory, such as the case of Phineas Gage
who had serious brain damage in an accident.
Gage survived but the damage to his brain affected his personality – he went from being calm and
reserved to being quick-tempered, rude and ‘no longer Gage’.
The change in Gage’s temperament following the accident suggests the frontal lobe may be
responsible for regulating mood.
LIMITATIONS
CONTRADICTORY RESEARCH – LASHLEY
The work of Lashley suggests higher cognitive functions such as learning processes, aren’t localised
but distributed more holistically in the brain.
Lashley removed areas of the cortex (up to 50%) in rats learning the route through a maze.
No one area was more important than any other in terms of the rats’ ability to learn the maze.
As learning required all the cortex rather than being confined to a particular area, this shows
learning is too complex to be localised and involves the whole brain.
NEURAL PLASTICITY IS A CHALLENGE TO THE LOCALISATION THEORY
When the brain has become damaged due to illness or accident, and a function has been
compromised or lost, the rest of the brain is able to reorganise itself to recover the function.
Lashley called this the LAW OF EQUIPOTENTIALITY – what happens is that other areas of the brain
‘chip in’ so the same neurological action can be achieved.
This doesn’t happen every time but there are lots of case studies of stroke victims recovering
abilities seemingly lost as a result of the illness.
