Biopsychology Flashcards
What is localisation?
The theory that specific areas of the brain are associated with particular physical and psychological functions
What is lateralisation?
The dominance of one hemisphere of the brain for particular physical and psychological functions.
What are the four main lobes in the brain
Parietal lobe
Occipital lobe
Frontal lobe
Temporal lobe
What does the motor cortex do and where is it?
BACK OF FRONTAL LOBE
Is responsible for the generation of voluntary motor movements.
Both hemispheres have a motor cortex, the right hem is responsible for the left side of the body’s movement and the left responsible for the right.
Different parts of the motor cortex exert control over different parts of the body. These are arranged logically.
What does the somatosensory cortex do and where is it?
PARIETAL LOBE, CLOSE TO THE MOTOR AREA
Detects sensory events arising from different regions of the body. Using information from the skin, the somatosensory cortex produces sensations of touch, pressure, pain and temperature, which it then localises to specific body regions
The amount of somatosensory area devoted to a particular body part, denotes its sensitivity. Receptors for our hands and face occupy over half the area.
Both hemispheres
What doe the visual centre do and where is it?
OCCIPITAL LOBE
Processing begins in the retina and then information is sent to the brain via the optic nerve. Most information then travels to the thalamus, which acts as a relay station, passing this information on the visual cortex.
Both hemispheres
The visual cortex contains different areas for colour, shape etc
What does the auditory centre do and where is it?
TEMPORAL LOBE
Is concerned with hearing. The auditory pathway begins in the cochlea where sound waves are converted to nerve impulses which travel via the auditory nerve to the auditory cortex.
Cochlea-Brainstem (basic decoding e.g. duration and intensity)- Thalamus (relay station/further decoding) -auditory cortex (recognition of and response to sound).
Outline Broca’s area
Named after french neuroscientist Paul Broca
“Tan” was a patient who could understand spoken language, but could not speak, nor express his thoughts in writing (broca’s or expressive aphasia)
Broca studies 8 other patients with similar language deficits. Post mortems revealed lesions to an area in the posterior portion of the frontal lobe of the left hemisphere. Patients with lesions on the right, did not have these language difficulties.
It was concluded that this area was essential for speech production.
Outline Wernicke’s area
Named after Carl Wernicke- German neurologist. Located in the posterior portion of the left temporal lobe.
Patients with lesions in this area could speak, but not understand language. Wernicke proposed that language involves separate motor and sensory regions located in different cortical regions.
Motor-broca’s
Sensory-wernicke’s
Wernicke’s area is thought to be responsible for the recognition and processing of language.
Evaluation of localisation
+ support for lang centres from aphasia studies
Expressive aphasia is an impaired ability to produce language.
Receptive aphasia is an impaired ability to understand language.
+wealth of evidence to support localisation from brain scans.
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.
+there is neurological evidence from cases of those who have had psychosurgery.
Walter Freeman developed lobotomy.
Neurosurgery is still used today in extreme cases of OCD and depression. Dougherty reported on 44 OCD patients who had undergone cingulotomy. Follow up at 32 weeks showed a third had met the criteria for successful response to surgery and 14% for partial response.
Findings show that over half of patients experienced no improvement, suggesting other factors may be involved and that localisation of function is an oversimplifying approach to the explanation and treatment of some behaviours.
-higher cognitive functions may not be localised
Lashley claimed that intact areas of the cortex could take over cognitive functions following injury to the area normally responsible for that function.
-communication may be a more important process to study than localisation.
Dejerine reported a case in which the ability to read was lost through damage to the connection between the visual cortex and Wernicke’s area.
-research into plasticity questions the argument of localisation.
Lashley described this as the law of equipotentiality, whereby brain circuits “chip in” so the same neurological action can be achieved. Although this doesn’t always happen, there are some well documented cases of stroke victims being able to recover those abilities that were seemingly lost through their illness.
Outline Lashley
Investigated rats ability to learn a maze and found that the basic motor and sensory functions were localised, but that higher mental functions were not. He found the effects of deliberate damage to between 10% and 50% of the rats cortex was determined by the extent, rather than the location, of the damage.
The more cortex he removed, the more the rats ability to learn the maze was affected.
Outline hemispheric lateralisation
Lateralisation : the dominance of one hemisphere of the brain for particular physical and psychological functions.
Left side of brain has language areas -Broca’s area and Wernicke’s area
Neural mechanisms for language are located primarily in the left half of the brain.
Research has also found that the right hemisphere excels at visual attention tasks and face recognition.
Therefore these functions are hemispherically lateralised.
The two hemispheres are connected via bundles of nerve fibres called the corpus callosum.
A way to investigate the different abilities of the two hemispheres is via the treatment for severe epilepsy includes cutting the corpus callosum- commisurotomy. This prevents violent electrical activity of a seizure from passing across the hemispheres.
Outline split brain research
Procedure -Sperry devised a general procedure in which an image or word could be projected to a patient’s right visual field and the same, or different image could be projected on the left visual field.
In a ‘normal’ brain the corpus callosum would immediately share the information between both hemispheres giving a complete picture of the visual world. However, presenting the image to one hemisphere of a split brain patient meant that the information could not be conveyed from that hemisphere to the other.
Study type one- describing what you see ; When a picture of an object was shown to a patient’s right visual field, the patient could easily describe what was seen. If, however, the same object was shown to the left visual field, the patient could not describe what was seen and typically reported nothing was there. This indicates that the language centres are in the left hemisphere. The patients inability to describe what was in the left visual field was because of the lack of language centres in the right hemisphere.
Study type two- recognition by touch ;although patients could not attach verbal labels to objects projected in the left visual field, they were able to select a matching object from a grab- bag using their left hand. The left hand was also able to select an object that was closely associated with an object presented to the left visual field. In each case the patient was not able to verbally identify what they had seen but could ‘understand’ what the object was.
Study type three- composite words ;if two words were presented simultaneously, one on either side of the visual field (‘key’ to left and ‘ring’ to right) the patient would write with their left hand the word key and say the word ring.
Evaluation of split brain research
High control- Sperry’s split brain research used scientific experiments with standardised procedures that were designed to test lateralisation in a highly controlled manner. This meant the findings would have been objective and valid.
Although there are issues with the conclusions drawn from Sperry’s research, it had contributed a greater understanding of brain processes and lateralisation i.e. that the left hemisphere is more geared towards verbal tasks and the right more visual.
Issues with generalisation- As fascinating as the findings from these studies are, many researchers have urged caution in their widespread acceptance, as split brain patients constitute such an unusual sample of people. There were only 11 who took part in Sperry’s research, all of whom had a history of epileptic seizures. It’s been argued that this may have caused unique changes in the brain that may have influenced findings.
Also some participants had experienced more disconnection of the hemisphere as part of their surgical procedure than others.
The control group Sperry used made up of 11 people with no history of epilepsy, may have been inappropriate.
Evaluation of lateralisation
Lateralisation changes with age-lateralisation of function appears not to stay exactly the same throughout an individual’s lifetime, but changes with normal ageing. Across many types of tasks and many brain areas, lateralised patterns found in younger individuals tend to switch to bilateral patterns in healthy older adults.
SZAFLARSKI Found that language became more lateralised to the left with increasing age in children and adolescents, but after the age of 25, lateralisation decreased with each decade of life.
Differences in function may be overstated-One legacy of Sperry’s work is a growing body of pop psychological literature that overemphasises and oversimplifies functional distinction between left and right hemispheres. Although the ‘verbal’ and ‘non-verbal’ labels can be usefully applied to summarise the differences between the two hemispheres, modern neuroscientists would contend that the actual distinction is less clear cut. In the normal brain the two hemispheres are in constant communication when performing every day tasks, and many of the behaviours typically associated with one hemisphere can be effectively performed by the other one when the situation requires.
There are individual differences- brain function lateralisation is evident in the phenomena of right-or-left handedness, but a persons preferred hand is not a clear indication of the location of brain function. Although 95% of right-handed people have left-hemisphere dominance for language, 18.8% of left handed people have right hemisphere dominance for language function. Additionally, 19.8% of left handed people have bilateral language functions. Even within various language functions, degree and even hemisphere of dominance may differ.
