Lecture 3 - Cerebral Asymmetry Flashcards
What’s the name of the process that implies that certain brain functions are dominated by one hemisphere ?
Lateralisation
What’s the definition of laterality ?
The idea that 2 cerebral hemispheres have separate functions
What are the anatomical differences between the 2 hemispheres ?
- R : larger/heavier, L : relatively more gray matter (more dense)
- Temporal lobes asymmetry
- Thalamus asymmetry : L>R
- Slope lateral fissure : R>L
- Frontal operculum differently organized
- Different distribution of neurotransmitters
What’s the difference between Neuroneal asymmetry & Genetic asymmetry ?
- Neuronal asymmetry : distinct patterns of dendritic branching
- Genetic asymmetry : epigenetic changes differentially affect the 2 hemispheres
Using Brain Stimulation on neurological patients, what is equally frequent when stimulating both hemispheres ?
- Localized movements
- Sensory experiences
- Light flashes
- Buzzing sounds
Using Brain Stimulation on neurological patients, what is equally frequent when stimulating L-hemisphere ?
- Speech acceleration
- Speech disruption
Using Brain Stimulation on neurological patients, what is equally frequent when stimulating R-hemisphere ?
- Report of visual/auditory memories/experiences
- Deja-vu
- Emotional responses
- Disruption of judgment of line orientation, facial expressions, short-term memory for faces
What’s “double disscociation” ?
When 2 areas of the Neocortex are functionally dissociated by 2 tests
= each test (measuring a specific function) is affected by a lesion in one zone but not in the other
What can be disturbed if the L temporal lobe is damaged ?
- Language
- Speech
- Writing
- Reading
What can be disturbed if the R temporal lobe is damaged ?
- Spatial tasks
- Non-verbal memory
- Singing/music/tonal patterns
What’s a commissurotomy ?
Dissection of Corpus Callosum
What’s a “split-brain” patient ?
A patient who had a commissurotomy
What happens if the Corpus Callosum is severed ?
- Each hemisphere functions independently
- No access to the other’s sensations, thoughts & actions
- Unaffected sensory & motor systems and their bodily receptors & effectors
What’s the WADA test ?
Anesthesia of one brain side with Carotid Sodium Amobarbital injection
What does the WADA test enable us to do ?
Study one hemisphere separately in functional absence of the anesthetized one
What happens if the L carotid area is briefly anesthetized ?
- Cannot speak
- Cannot move the R arm
- Cannot see on R visual field
Which hemisphere is most commonly dominant for language ?
L hemisphere for :
- 95% of R-handed
- 70% of L-handed
What’s the difference between a monaural presentation and a dichotic presentation ?
- Monaural : earing a sound only from one ear (goes to both hemispheres)
- Dichotic : earing a different sound in both ears (goes to contralateral hemisphere, ipsilateral pathway suppressed)
Is the auditory system completely crossed ?
No : ipsilateral & contralateral pathway from each ear, but crossed connections conduct more rapidly
What is each hemisphere dominant for in visual processing ?
- L-hemisphere : letters & words
- R-hemisphere : complex patterns & faces
What is each hemisphere dominant for in auditory processing ?
- L-hemisphere : verbal sounds & temporal structure of sounds (e.g. Morse code)
- R-hemisphere : non-verbal, emotional & musical sounds
What is each hemisphere dominant for in somatosensory processing ?
L-hemisphere (R hand) : objects & spatial patterns (e.g. Braille)
- R-hemisphere (L hand) : letters & temporal patterns (e.g. dynamic Braille)
Give 3 examples of behavioural measures
- Visual half field stimulation
- Dichotic listening tests
- Somatosensory tests
What are the limits of behavioural measures ?
- Indirect measures of lateralization
- Laterality measures often don’t correlate
- Effects of attention & behavioural strategies
What is each hand dominant for ?
- R hand (L-hemisphere) : verbal motor tasks
- L hand (R-hemisphere) : spatial motor tasks
What’s the difference between the 2 lateralization models ?
- Unilateral specialization model : each hemisphere has its own functions & methods, performs these independently
- Interaction models : both hemispheres capable of performing all cognitive functions, but are somewhat specialized
What can lead to variations in cerebral asymmetry ?
Individual differences :
- Handedness
- Sex
- Environment
In what type of persons are anatomical asymmetries more pronounced ?
R-handed persons
What are some sex differences in brain function ?
- Males (more asymmetry) : more intrahemispheric connections
- Females : more interhemispheric connections
Give an example of brain difference related to sexual orientation
Hypothalamus & hypothalamic connections differ in homosexual men (fMRI)
What are the different explanations of sex differences in cerebral asymmetry ?
- Hormonal effects
- Environment
- Maturation rate
- Cognitive mode
What hormones affect brain functions ?
- Testosterone (male)
- Estradiol (female)
Give 3 examples of environmental effects that could influence cerebral organization
- Different languages
- Sensory deprivation (deaf, blind)
- Environmental deprivation (orphans, SES)
How does the Inhibition Model explain hemispheric specialization ?
Each hemisphere has the capacity to perform certain functions, but the dominant hemisphere inhibits similar functions in the non-dominant one
What are the different theories regarding hand preference ?
- Environmental theories
- Anatomical theories
- Hormonal theories
- Genetic theories
What differences in brain structure favored female brains ?
- Larger language areas
- Larger medial paralimbic areas
- Larger lateral frontal areas
- Greater relative amount of grey matter
- More densely packed neurons in temporal lobe
- More gyri
- Thicker cortex
What differences in brain structure favored male brains ?
- Larger medial frontal areas
- Larger cingulate areas
- Larger amygdala & hypothalamus
- Larger overall white matter volume
- Larger cerebral ventricles
- More neurons overall
- Larger brain
To what is sex differences in brain structure related to ?
Differences in the distribution of estrogen and androgen (e.g. testosterone) receptors during development
What does the fluctuation of estrogen affect during the menstrual cycle ?
- Catecholamine : epinephrine & dopamine
- Stimulation of dopamine receptors
How does estrogen affects neuronal structure ?
Affects the number of dendritic spines on hippocampal neurons
