The Central Nervous System

THE CENTRAL NERVOUS SYSTEMYear 12 Psychology Unit 3 – The Conscious SelfArea of Study 1: Mind, Brain and BodyChapter 4 (pages 177 to 270)

PART 2 – Hemispheric Specialisation

THE HEMISPHERES OF THE CEREBRAL CORTEX

THE HEMISPHERES OF THE CEREBRAL CORTEX The cortex is made up of two separate but

linked hemispheres (halves): Each hemisphere (left or right) is responsible for

movement and sensation in the opposite side of the body.

Each hemisphere is also involved in specific functions i.e. the left side controls our ability to use and understand language.

The two hemispheres are linked by a bundle of nerves (neurons) called the Corpus Callosum

THE CROSS OVER…. Left controls Right.

Right controls Left.

No one knows why so don’t ask!

Note sexy yellow budgie smugglers.

HEMISPHERIC SPECIALISATION In general, the two hemispheres appear to be

replicas of each other. Each hemisphere can specialise or exert

greater control in various functions. However, for nearly all brain functions, both

hemispheres are involved and cooperate together.

Hemispheric Specialisation may also be known as hemispheric dominance or hemispheric lateralisation.

HEMISPHERIC SPECIALISATION Earliest evidence of hemispheric specialisation

came from observations of stroke victims or individuals with damage to one hemisphere.

Damage to the left hemisphere often resulted in difficulties with language-related activities.

Damage to the right hemisphere often resulted in difficulties with visual and spatial tasks. Visual and spatial skills generally involve mentally

picturing the way shapes/objects are related to one another or the surrounding environment.

Recent research supports these earlier findings.

LEFT HEMISPHERE

Verbal Functions: Recognition & use of words; Reading, writing, speaking, understanding speech.

Analytical Functions: Breaking a task down into key parts & approaching

it in a sequential, logical, ‘step-by-step’ way. Applying mathematical formula to solve a problem,

following a recipe, developing an argument, constructing a plan or creating a schedule.

RIGHT HEMISPHERE Non-Verbal Functions Creativity; Fantasy; Spatial and visual thinking;

Completing jigsaw puzzles, reading maps, visualising places or locations of objects.

Recognising faces, patterns & tunes; Appreciating music and artworks (not

necessarily producing them); Recognising emotions from facial cues (non-

verbal emotional expression).

3 MAIN APPROACHES TO RESEARCHING HEMISPHERIC SPECIALISATION Studying people with brain damage:

Stroke, aphasias, car accidents, sporting accidents, medical lobotomies.

Studying people who have had a split-brain operation: Cutting the corpus callosum to disconnect the

hemispheres – first used in the 1940s to minimise or stop severe cases of epilepsy.

Studying people with intact, undamaged brains: In the past, ethical issues have surrounded this but

modern technology allows less invasive techniques.

STUDYING PEOPLE WITH BRAIN DAMAGE - RESULTS Provides invaluable evidence about the

localisation of particular functions in one hemisphere but not the other: Damage to Broca’s and Wernicke’s

Language & language-dependent verbal tasks are a specialised function of the left hemisphere.

Neglect Syndrome (see pages 217 - 219) Caused by damage to the right hemisphere; left side of

their world does not exist. Spatial tasks are primarily the responsibility of the right

hemisphere.

SPATIAL NEGLECT Damage to the right parietal lobe. Results in the patient completely ignoring the

left side of their world, even the left side of their body.

Patients eat only the food on the right side of their plate, shave the right side of their face, wash the right side of their body etc.

A problem of attention, not blindness!

Activity: 4.15

What do you mean there’s something

wrong with my face?

STUDYING SPLIT-BRAIN OPERATION PATIENTS - RESULTS Roger Sperry (1974) was awarded the Nobel

prize for Physiology or Medicine in 1981 for his pioneering research on the relationship between brain and behaviour.

He found that split-brain patients can recognise a picture of an object but not name it. Visual recognition of objects is primarily right hemisphere, verbal language is primarily left. Cutting the ‘neural highway’ prevented the exchange of information between the hemispheres.

SPERRY’S EXPERIMENT Participant is seated behind a screen, focusing

on a black dot in the middle of the screen; Images or words are flashed onto the left or

right of the screen, i.e. into the participant’s left or right visual field;

Left visual field goes to the participant’s right hemisphere and right visual field goes to the participant’s left hemisphere;

Hidden behind the screen are several objects, matching the words or images shown – the participant cannot see them, but can feel them.

http://www.nobelprize.org/educational/medicine/split-brain/index.html

SPERRY’S EXPERIMENT:RESULTS Participants could name the objects/words that

flashed in their right visual field (and were sent to the left hemisphere).

Participants could not say what they saw when it was flashed in their left visual field (and was sent to the right hemisphere). They often denied that anything had been flashed on the screen.

To check that the participant could actually see the left visual field, even if they couldn’t say it, Sperry asked them to use their left hand to locate the matching object behind the screen. They were able to do this correctly.

Activity: 4.17