L7 Hemispheric Laterlisation Flashcards
Define Hemispheric lateralisation.
Hemispheric lateralisation refers to the notion that certain functions are
principally governed by one side of the brain
What has research demonstrated about lateralisation about specific areas
Systematic research has demonstrated that in most people language centres
are lateralised to the left hemisphere. The Broca’s Area was thought to be
responsible for the production of speech, however, this is now thought to
involve a wider network than just the Broca’s Area. Damage to the Wernicke’s
Area leads to expressive aphasia. Wernicke’s Area is considered to play a vital
role in understanding language/interpreting speech. Damage to the Wernicke’s
Area leads to receptive aphasia. The right hemisphere is dominant for visuospatial functions.
What is the right and left hemisphere responsible for ?
The right hemisphere of the brain is responsible for the left hand side of the
body, and the left hemisphere is responsible for the right hand side of the
body. If a patient is experiencing right sided paralysis this means there is
lateralised damage to the left hemisphere.
How are the two hemispheres connected
The two hemispheres are connected by a bundle of nerve fibres known as the
corpus callosum which enables information to be communicated between the
two hemispheres. Many researchers suggest that the two hemispheres work
together to form most tasks as part of a highly integrated system.
Evaluation of hemispheric lateralisation (supported by evolutionary perspective)
+ An advantage of hemispheric lateralisation is that it makes sense from an
evolutionary perspective. It increases neural processing capacity, which is
adaptive. By using one hemisphere to engage in a particular task it leaves the
other hemisphere free to engage in another function. Rogers et al. (2004)
found that hemispheric lateralisation in chickens is associated with an ability to
perform two tasks simultaneously (finding food and being vigilant for
predators).
Evaluation of hemispheric lateralisation (patterns makes sense)
Lateralisation patterns shift with age (Szaflarski et al 2006) with most tasks
generally becoming less lateralised in healthy adulthood.
Evaluation of hemispheric lateralisation (patients support’
Patients who have extensive damage to their left hemisphere can experience
global aphasia (loss of speech production and speech comprehension). This
suggests that language is lateralised to the left hemisphere.
Evaluation of hemispheric lateralisation (JW patient)
JW (a split-brain patient) developed the capacity to speak using his right
hemisphere, with the result that they could speak about information presented
in either the left visual field or the right visual field hemisphere (although he
was more fluent if information was presented in the left). It would appear that
language is not lateralised entirely to the left hemisphere (Turk et al. 2002).
Evaluation of hemispheric lateralisation (Danelli case study)
f one hemisphere is damaged, undamaged regions on the opposite hemisphere
can compensate. Danelli (et al. 2013) reported the case of EB, a 17-year-old
Italian boy who had virtually his entire left hemisphere removed at the age of
two and a half due to a huge benign tumour. EB’s language appeared almost
normal in everyday life in terms of vocabulary and grammar. However,
systematic testing revealed subtle grammatical problems as well as poorer than
normal scores on picture naming and reading of loan words. Language function
can be largely preserved after removal of the left hemisphere in childhood, but
the right hemisphere cannot provide, by itself, a perfect mastery of each
component of language.
What is split brain research / patients ?
In the past surgeons have cut the corpus callosum in order to prevent the
violent electrical activity caused by epileptic seizures crossing from one
hemisphere to the other. Patients who underwent this form of surgery are
often referred to as split-brain patients.
Who did the split brain research and what did it investigate
Sperry and Gazzaniga (1968) investigated split-brain patients. Information
from the left visual field goes into the right hemisphere, whereas information
from the right visual field goes into the left hemisphere. Because in split-brain
patients the corpus callosum has been severed there is no way for the
information presented to one hemisphere to travel to the other.
What was the split brain research /how does it work
Patients are asked to stare at a dot in the centre of a screen and then
information is presented in either the left or right visual field. They are then
asked to make responses with either their left hand (right hemisphere), right
hand (left hemisphere) or verbally (left hemisphere) without being able to see
what their hands were doing.
They may be flashed an image of a dog in their right visual field and then asked
what they have seen. They will be able to answer ‘dog’ because the information
will have gone into their left hemisphere where the language centres are. If a
picture of a cat is shown in their left visual field and they are asked what they
have seen they will not be able to say because the information has gone into
their right hemisphere, which has no language centres. However, they can draw
a picture of a cat with their left hand because the right hemisphere controls
this hand.
Evaluation of split brain research (drug therapy)
Split-brain patients have often had drug therapy for their epilepsy for much
longer than others, which may affect the way in which their brain works. This
means the findings of split-brain research cannot be generalised to the target
population.
Evaluation of split brain research (generalisation)
Many studies using split-brain patients have as few as three participants,
making it hard for results to be generalised to the target population.
Evaluation of split brain research (ecological validity)
