Biopsychology - Brain Localisation and Lateralisation Flashcards
What is the holistic theory of the brain? What was it replaced with?
Scientists in the early 19th century supported the holistic theory that all parts of the brain were involved in the processing of thought and action.
But specific areas of the brain were later linked with specific physical and psychological functions (localisation theory).
If an area of the brain is damaged through illness or injury, the function associated with that area is also affected.
What is localisation of function?
The idea that different parts of the brain perform different behaviours, processes or activities and are involved with different parts of the body. It follows then, that if a certain area of the brain becomes damaged through illness or injury, the function associated with that area will also be affected.
What is lateralisation?
The brain is divided into two symmetrical halves called left and right hemispheres. Some of our physical and psychological functions are controlled or dominated by a particular hemisphere - this is called lateralisation.
Which side of the brain controls which side of the body?
As a general rule, the activity on the left-hand side of the body is controlled by the right hemisphere and activity on the right-hand side of the body by the left hemisphere.
What is the cerebral cortex?
The outer layer of both hemispheres is the cerebral cortex. It is what separates us from other animals because the human cortex is much more developed. The cortex appears grey due to the location of cell bodies (hence “grey matter” to describe the surface appearance of the brain).
How is the cortex subdivided?
The cortex of both hemispheres is sub-divided into four lobes which are named after the bones beneath which they lie: the frontal lobe, the parietal lobe, the occipital lobe and the temporal lobe. Each one is associated with different functions.
What is the motor area?
At the back of the frontal lobe (in both hemispheres) is the motor area 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.
What is the somatosensory area?
An area of the parietal lobe that processes sensory information such as touch. The amount of somatosensory area devoted to a particular body part denotes its sensitivity.
What is the visual area?
A part of the occipital lobe that receives and processes visual information.
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. So damage to the left hemisphere, for example, can produce blindness in the right visual field of both eyes.
What is the auditory area?
Located in the temporal lobe and concerned with the analysis of speech-based information. Damage may produce partial hearing loss - the more extensive the damage, the more serious the loss.
What is Broca’s area?
An area of the frontal lobe of the brain in the left hemisphere (in most people) responsible for speech production.
Damage to this area causes Broca’s aphasia which is characterised by speech that is slow, laborious and lacking in fluency. Broca’s patients may have difficulty finding words and naming certain objects.
Patients with Broca’s aphasia have difficulty with prepositions and conjunctions.
What is Wernicke’s area?
An area of the temporal lobe (encircling the auditory cortex) in the left hemisphere (in most people) responsible for language comprehension.
Patients produce language but have problems understanding it, so they produce fluent but meaningless speech.
Patients with Wernicke’s aphasia will often produce nonsense words (neologisms) as part of the content of their speech.
What are the features of the left hemisphere?
- controls right side of body
- logic and language skills
- conscious thoughts
- speech (Broca’s area)
- reasoning
- science and maths
- written
- number skills
- right-hand control
What are the features of the right hemisphere?
- controls left side of the body
- creative skills
- motor tasks
- unconscious thoughts
- facial recognition (inability = prosopagnosia)
- imagination
- intuition
- insight
- holistic thought
- music awareness
- art awareness
- spatial awareness
- left-hand control
What is the corpus callosum?
The two hemispheres are connected through nerve fibres called the corpus callosum which facilitate interhemispheric communication.
What are the strengths of localisation of function?
- brain scan evidence of localisation
- neurosurgical evidence
- case study evidence
What are the weaknesses of localisation of function?
- existence of contradictory research
- neural plasticity challenges the localisation theory
- case study evidence
What brain scan evidence is there of localisation?
Peterson et al. used brain scans to demonstrate how Wernicke’s area was active during a listening task and Broca’s area was active during a reading task, suggesting that these areas of the brain have different functions.
Similarly, a study of long-term memory by Tulving et al. revealed that semantic and episodic memories reside in different parts of the prefrontal cortex. There now exists a number of highly sophisticated and objective methods for measuring activity in the brain which provide sound scientific evidence of localisation of brain function.
What neurological evidence is there for localisation?
Neurosurgery is used in extreme cases of OCD and depression. Surgically removing or destroying areas of the brain to control aspects of behaviour was developed in the 1950s by Walter Freeman - though these early attempts were brutal and imprecise.
Dougherty et al. (2002) reported on 44 OCD patients who had undergone a cingulotomy - a neurosurgical procedure that involves lesioning of the cingulate gyrus. At post-surgical follow-up after 32 weeks, 1/3 had met the criteria for successful response to the surgery and 14% for partial response.
The success of procedures like this strongly suggests that symptoms and behaviours associated with serious mental disorders are localised.
What case study evidence is there for localisation?
Phineas Gage
- rod
- changed personality (temperament) from calm and reserved to quick-tempered and rude
- suggests the frontal lobe may be responsible for regulating mood
- specific parts of the brain perform specific functions
What case study evidence is there against localisation?
Jodie Miller
- epilepsy
- removed right hemisphere
- left took over
How is Lashley’s research a weakness of localisation?
The work of Karl Lashley (1950) suggests that higher cognitive functions, such as the processes involved in learning, are not localised but distributed in a more holistic way in the brain.
Lashley removed areas of the cortex (between 10 and 15%) in rats that were learning a maze. No area was proven to be more important than any other area in terms of the rats’ ability to learn the maze.
The process of learning appeared to require every part of the cortex, rather than being confined to a particular area. This seems to suggest that learning is too complex to be localised and requires the involvement of the whole brain.
However, animal research has limitations.
How is plasticity/cortical remapping a weakness of localisation?
When the brain has become damaged and a particular function has been compromised or lost, the rest of the brain appears able to reorganise itself in an attempt to recover the lost function.
Lashley described this as the law of equipotentiality whereby surviving brain circuits ‘chip in’ so the same neurological action can be achieved.
Although this does not happen every time, there are several documented cases of stroke victims being able to recover those abilities that were seemingly lost as a result of the illness.
What are the key features of split-brain research?
- hemispheric lateralisation
- split-brain studies involved a unique group of individuals
- Sperry devised a unique procedure to test his split-brain patients
- describing what was seen
- recognition by touch
- composite words and matching faces
