**L7 - Hemispheric Lateralisation Flashcards
what is HEMISPHERIC LATERALISATION?
HEMISPHERIC LATERALISATION refers to the NOTION THAT CERTAIN FUNCTIONS are PRINCIPALLY GOVERNED by ONE SIDE OF THE BRAIN
what has SYSTEMATIC RESEARCH SHOWN about LEFT HEMISPHERE lateralisation? - PT 1
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
what has SYSTEMATIC RESEARCH SHOWN about LEFT HEMISPHERE lateralisation? - PT 2
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.
what has SYSTEMATIC RESEARCH SHOWN about RIGHT HEMISPHERE lateralisation?
The RIGHT HEMISPHERE is DOMINANT for VISUO-SPATIAL FUNCTIONS. 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
+ ROGERS ET AL (EVALUATION OF HEMISPHERIC LATERALISATION)
+ an advantage of HEMISPHERIC LATERALISATION is that it MAKES SENSE from an EVOLUTIONARY PERSPECTIVE.
It INCREASES NEURAL 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 found that HEMISPHERIC LATERALISATION IN CHICKENS is ASSOCIATED WITH AN ABILITY to PERFORM TWO TASKS SIMULTANEOUSLY (finding food and being vigilant for predators)
- SZAFLARSKI ET AL (EVALUATION OF HEMISPHERIC LATERALISATION)
- a weakness of this theory is research conducted by SZAFLARSKI ET AL. The research showed that LATERALISATION PATTERNS SHIFT WITH AGE with MOST TASKS becoming LESS LATERALISED IN HEALTHY ADULTHOOD
+ GLOBAL APHASIA (EVALUATION OF HEMISPHERIC LATERALISATION)
+ 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
- JW (EVALUATION OF HEMISPHERIC LATERALISATION)
- 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
- DANELLI ET AL (EVALUATION OF HEMISPHERIC LATERALISATION) - PT 1
- if ONE HEMISPHERE IS DAMAGED, UNDAMAGED REGIONS on the OPPOSITE HEMISPHERE CAN COMPENSATE
DANELLI ET AL 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
- DANELLI ET AL (EVALUATION OF HEMISPHERIC LATERALISATION) - PT 2
- 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 abs READING OF LONE 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?
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
what did SPERRY and GAZZANIGA do?
SPERRY and GAZZANIGA 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 in ONE HEMISPHERE to TRAVEL TO THE OTHER
what happens during SPLIT BRAIN RESEARCH? - PT 1
Patients are ASKED TO STARE AT A DOT I. The CENTRE OR 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
what happens during SPLIT BRAIN RESEARCH? - PT 2
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 RIGHT HAND because the RIGHT HEMISPHERE CONTROLS THIS HAND
