Lecture 6 - Notes PY2245 PDF

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What is Hemispheric Lateralisation? 1.

Define ‘HEMISPHERIC LATERALISATION’.



Refers to the idea that the two halves of the brain are functionally different.



Certain mental processes and behaviours are controlled by one hemisphere rather than the other.

2.

Outline the role of the ‘LEFT HEMISPHERE’.



Responsible for producing and understanding language and in controlling movement on the right.

3.

Outline the role of the ‘RIGHT HEMISPHERE’.



Specialises in perceiving and synthesizing non-verbal information – E.G. music and facial expressions.

4.

Briefly outline 4 variables that complicate research on laterality.

1.

Laterality is relative.

2.

Cerebral site is as important in understanding brain function as the cerebral side.

3.

Environmental factors affect laterality.

4.

A range of animals exhibit laterality.

5.

Outline ‘Laterality is relative’ as a variable that complicates research on laterality.



Both hemispheres participate in nearly every behaviour.



I.E. although the LH is important in producing language the RH has language capabilities.

6.

Outline ‘Importance of Cerebral Site’ as a variable that complicates research on laterality.



It can be difficult to localise lesions in neurological patients to one hemisphere.



Cortical functions should be views as localised and hemispheric side as a feature of lateralisation.

7.

Outline ‘Importance of Environmental Factors’ as a variable that complicates research on laterality.



Cerebral organisation of some left handed females are less symmetrical than right handed males.

8.

Outline ‘Animals Exhibit Laterality’ as a variable that complicates research on laterality.



Songbirds, rats, cats, monkeys and apes have functionally and anatomically asymmetrical brains.

The History of Hemispheric Lateralization 5.

Outline Dax’s (1836) Contributions to Hemispheric Lateralisation.



Dax was the first to recognise that language problems are related to damage to the left hemisphere.



He came to this conclusion via the observation of 3 patients.

6.

Outline Gall’s (1796) Contributions to Hemispheric Lateralization.



Promoted the idea that cognitive abilities are represented in different cortical areas of the brain.



Joseph used size and location of the bumps on the head to determine an individual’s cognitive profile.



He attempted to analyse abstract functions – E.G. conscientiousness, secretiveness and charity.



Additionally he denoted the strength of a function with the size of the corresponding bump.

7.

Outline Broca’s (1861) Contributions to Hemispheric Lateralization.



Broca treated a patient nicknamed ‘tan’ as that was the only word he was able to say.



Tan could understand spoken language but was unable to produce coherent speech.



A post mortem examination revealed that he had a lesion in the posterior frontal lobe.



The lesions position was consistent with Gall’s idea that language is localized on the left frontal lobe.



Findings from 8+ patients who had suffered from aphasia confirmed that they had left frontal lesions.

8.

Define ‘BROCA’S AREA’.



Refers to the region of the brain that is important for speech production and motor functions.



Broca concluded that ‘we speak with the left hemisphere’ – the frontal region was called Broca’s area.

9.

Define ‘APHASIA’.



Refers to the inability to produce or understand speech as a result of brain damage.

10. Define ‘BROCA’S APHASIA’.



A type of aphasia characterised by partial loss of the ability to produce spoken language.

11. Outline Wernicke’s (1874) Contributions to Hemispheric Lateralization. 

Claimed that lesions in the posterior temporal lobe result in different types of language difficulties.



This affects comprehension more than speech production.

12. Define ‘WERNICKE’S AREA’. 

Refers to the region of the brain that is important for language development.



It is located in the temporal lobe of the left hemisphere.

13. Define ‘WERNICKE’S APHASIA’. 

A type of aphasia characterised by deficits in the comprehension of language.

14. Outline the functions of the Right Hemisphere. 

This hemisphere is dominant for visuo-spatial processing.

15. Outline the functions of the Left Hemisphere. 

This hemisphere is dominant for processing language.

16. Define ‘WADA TEST’. 

Test used to assess language dominance by injecting one hemisphere at the time with a barbiturate.



After doing so the effects on language functions are observed.

17. Outline the results of the research produced by the WADA test. 

Language is represented in the left hemisphere in 95% of STRONG right-handers.



Language is represented in the left hemisphere in 85% of people with a LESS CLEAR hand preference.



Language is represented in the left hemisphere in 70% of left handers – 15% bilateral and 15% right H.

Anatomical Differences 18. Outline 7 Main Anatomical Differences Between the Left & Right Hemispheres.

1.

RIGHT hemisphere is slightly larger and it weighs more.

2.

RIGHT hemisphere contains less grey matter.

3.

RIGHT hemisphere – the frontal lobe extends further and it is wider.

4.

LEFT hemisphere – the sylvian fissure is longer in the left.

5.

LEFT hemisphere – the slope is greater.

6.

LEFT hemisphere – the planum temporale is larger.

Anatomical Differences & Function

19. Outline the Anatomical & Functional Aspects of the Planum Temporale. 

In some peoples brains the planum temporale is five times larger on the left than on the right.



Differences are observed in new born babies suggesting a genetic predisposition.



The size of the planum temporale appears to relate to language dominance.



This is because most right-handers have larger planum temporal.

20. Outline the Anatomical & Functional Aspects of the Sylvian Fissure. 

People with language lateralised in the left hemisphere have a different sylvian fissure slope.



This has not been found in people with right hemisphere dominance or with bilateral dominance.

Research With Split Brains Patients 21. Define ‘SPLIT BRAIN PATIENTS’ 

Individuals who have undergone a commissurotomy.

22. Define ‘COMMISUROTOMY’. 

Refers to a surgery that has severed the main tracts of fibres connecting the two hemispheres.

23. Outline the History of Commissurotomy’s. 

This surgery was carried out in the sixties on a small number of patients with life threatening seizures.



As seizures could not be prevented the surgery hoped to be able to confine them to one hemisphere.



These surgeries are not carried out anymore due to the aversive side effects and new drugs.



Each hemisphere received and processed input but was unable to share information with the other.

The Structures Responsible for Communication Between Hemispheres 24. Name 2 Structures Responsible for Communication Between Hemispheres. 1.

Corpus Callosum

2.

Anterior Commissure

25. Define ‘CORPUS CALLOSUM’. 

Massive neural tract of 200-250 millions fibres connecting symmetrical regions in the 2 hemispheres.



Different types of information are transferred across by different parts of the callosum.



E.G. motor information is transferred in the middle part of the callosum.

26. Define ‘ANTERIOR COMMISSURE’. •

A smaller bundle of fibres connecting the anterior parts of the two hemispheres.

Methodology 27. Outline an advantage of researching using split brain patients. 

It is possible to direct input selectively to one hemisphere.



In split brain patients this input is unable to cross over to the other hemisphere.



Therefore, it is possible to investigate the effects of an input (stimulus) on just one brain hemisphere.

28. Outline the effects of visual input on split brain patients. 

Using a tachistoscope visual information can be presented to each visual field independently.

 

Participants fixate on a centre point marked by a cross. An image is then flashed in one visual field for 50 milliseconds.



Information presented to one visual field is processed by the hemisphere specialised to receive it.



E.G. words presented to the left hemisphere are processed more efficiently than on the right.

29. Define ‘DICHOTIC LISTENING’. 

Experimental procedure whereby an individual listens to 2 auditory streams presented to the 2 ears.

30. Outline the effects of auditory input on split brain patients. 

Presented pairs of spoken digits simultaneously through headphones.



One digit was heard in each ear – subjects heard 3 pairs of digits and were asked to recall them.



Subjects recalled more digits that had been presented to the right ear than the left.



Kimura found that the ear we attend to depends on the task:

1.

We attend to the right ear if we are listening to speech

2.

We attend to the left ear if we are listening to music.



Patients with corpus callosum damage exhibit an inhibition of words present to the left ear.



Even though they can recall words presented to this ear, there is no competing stimulus to the right.

31. Outline the asymmetry in the somatosensory system. 

Researchers blindfolded participants whilst they performed various tasks separately with each hand.



Investigators can identify differences in each hands efficiency.



Researchers compared the performance of the left hand and right hand in recognising shapes etc.



The left hand of right handed participants is superior at nearly all tasks.

32. Outline the effects of tactile input on split brain patients. 

What is touched by one hand will be known by contralateral hemisphere.

 Thus, with the left hand it will be known by the right hemisphere and not by the left. 33. Outline the Results of Findings from Split Brain Research. 

Research has confirmed that the left hemisphere is dominant for language.



They also have given us insights into the linguistic abilities of the right hemisphere.



The right hemisphere is not completely illiterate as it can understand simple sentences.

34. Outline Experiments Carried Out with Patients & Controls. 

The right hemisphere has been found to be dominant in the processing of faces.



If a split brain patient is presented with a chimeric face they will be unaware of anything wrong.



The left part of the face will be processed by the right hemisphere and the right part by the left.



If asked to identify the picture among others patients will pick the face corresponding to the left half.



This is because it is this half that has been processed by the right hemisphere.

35. Identify 2 Limitations of Split Brain Research. 1.

The surgery may have produced some brain damage.

2.

Unusual lateralization of functions.

Lesions to the LEFT HEMISPHERE

36. Lesions in the left hemisphere. 1.

Aphasia – difficulties in comprehending and producing speech.

2.

Dyslexia and Dysgraphia – difficulties with reading and spelling.

3.

Agnosia – difficulties in knowing the meaning of objects.

4.

Apraxia – difficulties in carrying out complex movements.

5.

Poor STM and LTM for verbal materials

Lesions to the RIGHT HEMISPHERE 37. Lesions in the right hemisphere. 1.

Difficulties processing music.

2.

Difficulties reading in Braille.

3.

Agnosia – difficulties in recognizing faces and complex spatial objects.

4.

Apraxia – difficulties with movements in spatial patterns.

5.

Difficulties with directions and spatial orientation.

6. Poor STM and LTM for visuo-spatial materials...