2. Hemispheres Flashcards
Corpus callosum
A large collection of axons which serve as a bridge for the two hemispheres to communicate
Contralateral organisation
Controlling the opposite side
Left visual field
The right halves of each eye
Right visual field
The left halves of each eye
Left hemisphere
Language
Production of speech
Reading, writing
Verbal memory
Right hemisphere
Emotional perception
Spacial awareness
Faces
Understands speech, cannot produce it
Cerebral lateralization
Hemispheres/different areas of the brain developing different, specialised skills
Cause of lefthandedness
Either the right or left hemisphere will be dominant, resulting in left or right handedness
Unclear why left-handedness is rare as it does not cause any severe disadvantages
Possible causes of lefthandedness
- Fetus predisposition
- Which hand you lay on more
- Genetics
- Slower development of RH
- Prenatal stress (infections, increased testosterone)
- Vitamin D levels
- Testosterone levels
Right-sided world hypothesis
World is designed for right-handed people so left-handed people have more accidents
Survival of the unexpected
Gives left-handed people certain advantages like in sports and music
Lateralization
Division of responsibilities between the hemispheres
Split brain patients
Severing of the corpus callosum to treat severe epilepsy
Effects of split brain on epilepsy
- Prevents the seizure crossing over to the other side of the brain
Seizures occur on only one side of the body - Less frequent
- Shorter
- Normally epileptic activity bounces between the hemispheres
Behaviour changes in split brain patients
- They can use their hands independently in ways that we can’t
- Drawing two different shapes simultaneously or the same shape at different speeds
Behavioural effects when stimuli is presented to only one side of the body
- Information cannot cross to the other hemisphere
- Can only point to what each hemisphere saw
- Cannot verbally describe what the right hemisphere saw but is able to point it out
- Initially, patients experience conflicts between the two sides of their body as they don’t communicate and do separate, opposing things
- e.g. right hand picks up groceries, left hand puts them back
- This usually passes with time
Unchanged behaviour in split brain patients
- There is no effect on familiar tasks like tying shoes
- Intellect, motivation, speech are all the same
Interpreter
the tendency of the left hemisphere to explain and defend its actions when the cause is unclear
Split brain & Children
- Behaviours of split-brain patients are comparable to those in young children as the corpus callosum develops from 3-5 years old
- Sometimes, children are born without the corpus callosum - both hemispheres will be active during speech
- Ordinarily, both hemispheres are in charge of language but the left will eventually block the right, this doesn’t happen without a corpus callosum
Planum temporale
- Comprehension of language
- Damage - aphasia (trouble with language)
- Bigger in the left hemisphere
Heschl’s Gyrus
- Located in the later fissure
- Primary auditory cortex
- Asymmetrical - right one is bigger than the left - might have an impact on split brained patients
- Bigger in the left hemisphere
3 Theories about Cerebral Lateralization
Analytic (LH) and Synthetic (RH) Theory
Motor Theory
Linguistic Theory
Analytic (LH) and Synthetic (RH) Theory
2 basic modes of thinking, one for each hemisphere
Analytic (LH) - logical, computer-like thinking
Synthetic (RH) - organizes & processes information as a whole, not the sum of its parts
Frontal operculum AKA Broca’s Area
Speech production; more pronounced in LH
Motor Theory
LH is specialised to the control of fine movements, with speech falling under this category
Linguistic Theory
The primary role of the LH is language
Opposes prior two theories which see language as a secondary role of the LH
Evidence: damage leads to disruption of sign language, but not pantomime gestures
Sodium Amytal Test
Sodium amytal is injected into the carotid artery on one side of the neck to numb certain parts of the corresponding hemisphere for a short time
Purpose: to study lateralization
Dichotic Listening Test
Headphones play different numbers in each ear, see which one the participant heard to show which hemisphere was more dominant
What type of matter are axons?
White matter
What type of matter are neuron bodies
Grey matter
Functional brain imaging
fMRI, PET - brain activity; LH - language
Visual completion
being unaware of a scotoma (blind spots) -> brain filling them in by using information from the surrounding areas of the visual field
Helping-hand phenomenon
one hand grabbing the other hand and redirecting it toward the stimuli thought to be right by that certain hemisphere
Cross-cueing
hemispheres communicating with each other by an external route
