Hemispheric lateralisation

• What are neuroscientists interested in ?

  Neuroscientists are interested in whether certain activities and behaviours are controlled/dominated by one hemisphere, rather than the other i.e. lateralisation
• the right hemisphere controls activity on the left side of the body and vice versa 
• Recap on Paul Broca ?

  In 1861, Paul Broca established that damage in one particular area of the left hemisphere (now known as Broca’s area) resulted in language deficits, whereas damage to the same area of the right brain hemisphere did not have the same consequence...

  This suggests that for most of us, language is subject to hemispheric lateralisation as specialised areas associated with language are found in one of the brain’s hemispheres, rather than both!
• What does research suggest about left and right hemispheres?

  research suggests that that the right hemisphere excels at visual motor tasks and facial recognition
• What’s epilepsy associated with ?

  Associated with uncontrollable seizures
• Facts about epilepsy?

  Relatively widespread condition affecting around 456,000 people in the UK

  Usually begins around childhood but it can start at any age

  Around 1 in every 280 children is affected by it
• What’s a common myth about epilepsy?

  A common myth is that flashing lights bring it on but this only accounts for about 10% of all epileptic sufferers that have photo sensitive epilepsy
• Can medicine help epilepsy?

  Modern medicines can usually control it but surgery is sometimes still used in some cases
• What’s the epilepsy surgery?

  Surgeons cut through the bundle of nerve fibres that form the corpus callosum (last line of defence!)

  Disconnection can vary

  The aim of the procedure is to prevent violent electrical activity crossing from one hemisphere to the other

  ‘Split brain’ patients were used in Sperry and Gazzaninga’s research
• What did sperry and gazzaniga took advantage of?

  Sperry and Gazzaniga took advantage of the fact that information from the left visual field goes to the right hemisphere and information from the right visual field goes to the left hemisphere.
• What happens with the corpus Callum in spilt brain patients?

  Because the corpus callosum is cut in split brain patients, the information presented to one hemisphere has no way of travelling to the other hemisphere and can only be processed in the hemisphere that received it.
• Method of split brain patients ?

  Participants are asked to respond to visual information

  • The split-brain patient is asked to fixate on to a dot in the middle of the screen

  • The visual information is presented to either the right or left visual field for less than 1/10 of a second (small presentation time)

  • The patient has to name the visual information that was presented to them
• Sperry’s and Gazzaniga aim ? 

  The aim of their research was to examine the extent to which the two hemispheres are specialised for certain functions.
• Sperry’s and Gazzaniga method?

  An image/word is projected to the patient’s left visual field (which is processed by the right hemisphere) or the right visual field (which is processed by the left hemisphere). When information is presented to one hemisphere in a split-brain patient, the information is not transferred to the other hemisphere (as the corpus callosum is cut).
• Method (2)

  In the describe what you see task, a picture was presented to either the left or right visual field and the participant had to simply describe what they saw.

  In the tactile test, an object was placed in the patient’s left or right hand and they had to either describe what they felt, or select a similar object from a series of alternate objects.

  Finally, in the drawing task, participants were presented with a picture in either their left or right visual field, and they had to simply draw what they saw. 
• Sperry and Gazzaniga results?

  Ppts would only recognise stimuli if the stimuli were presented again to the same visual field.If ppts we’re shown stimuli in the rvs but the shown the same stimuli to the LVF,they would claim to have not seen it before.Imformation presented to the RVF (left hemisphere) could be described in speech and writing (with the right hand). If the same information is presented to the LVF (rh), the ppt insisted he either didn’t see anything and couldn’t describe it in speech/writing.
• Sperry and Gazzaniga conclusion?

  The findings of Sperry and Gazzaniga’s research highlights a number of key differences between the two hemispheres. Firstly, the left hemisphere is dominant in terms of speech and language. Secondly, the right hemisphere is dominant in terms of visual-motor tasks.
• What have we learned from split-brain research?

  Work with split brain patients has discovered a number of differences between the two hemispheres, e.g. that the left hemisphere is responsible for speech and language and the right hemisphere specialises in visual-spatial processing and facial recognition.

  However, split-brain research has not shown that the brain is organised into discrete regions with specific sections responsible for specific tasks. Instead, it suggests that the connectivity between the different regions is as important as the operation of the different parts.
• What’s some evaluations for split brain/hemispheic lateralisation?

  :) one strength is support from more recent split-brain studies - luck et al 

  :) one strength is evidence of lateralised brain functions in normal brains

  :( one limitation is that casual relationships are hard to establish - sperry