8 - Hemispheric Lateralisation - Split Brain

• Hemispheric Lateralisation???


  Hemispheric Lateralisation - The brain is lateralized i.e. 2 sides (hemispheres).

  The brain is divided in 2 hemispheres - the left and right. 

  The activity on the left side of the body is controlled by the right brain hemisphere, whereas the activity on the right side of the body is controlled by the left. This is known as hemispheric lateralisation.
• Localised?


  Localised:

  • Some functions are localised and appear in both left & right hemispheres (LH & RH).
  • E.g. auditory, visual, motor, somatosensory areas.
• Contralateral: 


  • In the motor area, the right hemisphere controls the left side of the body and vice versa (cross-wired).
• Localised and lateralized:

  • Two main language centres are in the LH (for most people) - Broca’s area (left frontal lobe), Wernicke’s area (left temporal lobe).
  • RH produced rudimentary words but provided emotional context. LH may be the analyser, RH the synthesiser.
• Contralateral & ipsilateral:


  • Left visual field of both eyes is connected to the Right hemisphere and the RVF of both eyes is connected to the LH
  • ENables the visual areas to compare the slightly different perspective from each eye and aids depth and perception.
  • Same arrangement for auditory areas.
• What left and right sides of the brain do?

  ?

  A) ?

  B) ?

  
• Hemispheric Lateralisation diagram explain?

  So both eyes information they see in the LVF goes to the RH.

  Both eyes information they see in the RVF goes to the LH.

  CHECK THIS INFO TO MAKE SURE CORRECT

  A) ?

  
• 2 hemispheres are connected by:


  • A thick band of nerve fibres called CORPUS CALLOSUM
• Why might it be necessary to sever (cut) this bundle of nerve fibres?

  • Prevent seizures from spreading from one half of the brain to the other.
  • What is this procedure called = Commissurotomy/corpus callosotomy
  • Who does the term split brain patient refer to? = Patient who had corpus callosum cut (brain separated)
• In which hemisphere is the language centre (Wernicke & Broca)?


  • Left
• With which visual field would a split brain patient need to see an object in order to state the name of it? 

  • Right (only effects split brain patients).
• What is the term for an inability (or impaired ability) to understand or produce speech, as a result of brain damage>

  • Aphasia
  • Broca's Aphasia - hard to produce 
  • Wernicke's Aphasia - hard to understand
• Split Brain Patient?

  ?

  A) ?

  
• Research - Who & Yr?

  • Sperry & Gazzaniga (1968)
• Right & left brain functions (again but added to)

  ?

  A) ?

  
• Background to Sperry?


  • Some epileptic patients underwent surgery called commissurotomy to cut the corpus callosum, the main bundle of neuronal fibres connecting the 2 sides of the brain.
  • The purpose was to reduce the damage caused by an epileptic seizure by containing it in one side of the brain.
  • Sperry was able to take the opportunity of studying patients with ‘split brain’ in order to determine whether there are differences between the 2 hemispheres of human brains that were specialised for different functions. Hemispheric lateralisation.
• Sperry and Gazzaniga (1968) AIM?


  Aim = to examine the extent to which the 2 hemispheres are specialised for certain functions (Investigate the functions of both hemispheres) AND find the effects of hemisphere deconnection in split brain patients.
• Sperry and Gazzaniga (1968) PROCEDURE - PART 1


  • 11 split brain ppts (males & females) - (‘Split Brain’ = 2 hemispheres surgically separated by cutting connections e.g. corpus callosum - Used to treat severe epilepsy to reduce ‘electrical storm’ across hemispheres).
  • Sat in front of projector screen & focused on fixation point in middle. Visual stimuli (image/word) appear for 1/10 of a second on screen.
  • Stimuli presented to one visual field or both.
  • Image/word projected to RVF (processed by LH) & same/different image could be projected to LVF (processed RH).
• Sperry and Gazzaniga (1968) PROCEDURE - PART 2

  • Below screen was gap so ppts could reach objects which been placed in ‘grab bag’ but couldn’t see this.
  • ‘Normal’ brain corpus callosum immediately share info between RH & LH giving complete picture of visual word.
  • Split brain individual = presenting image to 1 hemisphere = info couldn't be conveyed from one hemisphere to other.
• Sperry and Gazzaniga (1968) FINDINGS


  • Pictures
  • Tactile Tests
  • Drawing Tasks
  • Objects
• Sperry & Gazzaniga (1968) - Pictures

  Describing what you see: PICTURES

  • When an image was presented to the RVF they could describe what was seen.
  • When an image was shown to LVF ppts could NOT describe what they saw and insisted they hadn’t seen anything (due to a lack of language centre in RH - Could draw with left hand & point to matching pic with left hand).
• Sperry & Gazzaniga (1968) - Tactile Tests


  Objects placed in right hand

  • Could describe verbally what they felt/were holding OR they could identify a test object presented in the right hand by selecting a similar object from a group of objects (could select a similar object from a group of objects)

  Objects placed in left hand

  • Could NOT describe what they felt/what they were holding = guessed
  • BUT Left hand could identify the test object presented in the left hand by selecting the object from the group. (
  • but they could identify a similar object from a group of objects with their left).
• Sperry & Gazzaniga (1968) Drawing tasks

  Pic presented to RVF

  • If right hand attempts to draw a pic, a pic not as clear as the left hand.
  • Showing superiority for RH for visual motor tasks.
  • Could name pic.

  Pic presented to LVF

  • Left hand draw better & clearer and better pic vs right hand (even though all pps were right handed)
  • Unable to name pic

  When there was a nude pin up image and this was shown to LVF ppt giggled & blushed but could not say why/reported seeing nothing.
• Speerry & Gazzaniga (1968) - Objects


  • Object shown to RVF:
  • Participant can describe what is seen (language centres in LH)
  • Object shown to LVF:
  • Cannot name object (no language centres in RH)
  • Can select matching object behind screen using left hand
  • Can select objects closely associated with the picture (e.g. ashtray if picture of cigarette).
• Sperry & Gazzaniga (1968) - CONCLUSIONS?


  Conclusion:

  • Left hemisphere dominant/associated for speech & language
  • Right hemisphere dominant for visual motor tasks, drawing, emotion, facial recognition 
  • Clear evidence for lateralisation of brain function.
  • Drawing/Emotion/facial recognition associated with the right.
  • Also provided some empirical evidence for the role of the unconscious mind (nude pin up).

  Demonstrates how certain functions are lateralized in the brain, shows that LH is verbal and the RH is ‘silent’ but emotional.