cerebreal assymetry Flashcards
what brain area connects\integrates the two hemispheres?
-the corpus callosum
what is lateralization?
-most tasks require a parallel use of both spheres, but when a certain function is dominated by a hemisphere=laterilization
-Laterality: idea that two cerebral hemispheres have separate functions
what is anatomical asymmetry?
-Physical asymmetry between the hemispheres
-differences in position and size
(R larger, L more dense)
-Differences in size
of parts of the temporal lobe
(primary auditory cortex,
Wernicke’s area) and
thalamus
-broca’s area is differently organized
(surface larger R, sulci larger L)
-Distribution of neurotransmitters
what is neuronal asymmetry?
Distinct patterns of dendritic branching (left
operculum(Broca))
what is genetic asymmetry?
epigenetic changes differentially affect the 2 hemispheres
(and this differs per brain region)
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what are the different kinds of brain asymmetry?
-anatomical:
neuronal
genetic
-behavioural
how do you test for Asymmetries in neurological patients?
-Brain stimulation
* Patients with lateralized lesions
* Commissurotomy patients
* WADA test
how do you test for Behavioral asymmetries in the intact brain
-Visual system
* Auditory system
* Somatosensory system
how does brain stimulation work?(neurological patients)
1)Direct electrical cortical stimulation (mapping) before surgery
- when stimulating the left hemisphere, speech acceleration and disruption r the most frequent effects
.when stimulating the right: Report of visual/auditory
memories/experiences
* Deja-vu
* Emotional responses (e.g. fear)
* Disruption of judgement of line
orientation, facial expressions,
short term memory for faces
equally frequent when stimulating left/right:
* Localized movements, sensory
experiences, light flashes, buzzing sounds
what are functions mostly done by the left?
Language
Speech
Writing
Reading
what are functions mostly done by the right?
Spatial tasks
Non-verbal memory
Singing/music/tonal
patterns
what are Commissurotomy patients?
they are split-brain patients:
- the cortical connections between homotopic points of hemispheres are severed
-thus each hemisphere acts independently
-the cortical connections to the sensory and motor system r still intact
what’s the WADA test?(Asymmetries in neurological patients)
-anesthesia of one brain side with Carotid Sodium Amobarbital Injection
-enables us to study one hemisphere separately in
functional absence of the anesthetized one.
– Used for epileptic surgery to determine lateralization of
(language) function
* ± 95% of right-handed and 70% of left-handed people
have a L hemisphere dominance for language
* Safe procedure but performed less nowadays
what is the dichotic listening task? why is it done? (behavioral asymmetries)
-a psychological test where different audio messages are presented to each ear simultaneously, and the participant must focus on one message while ignoring the other.
-it examines how each hemisphere processes auditory information. Typically, the right ear (linked to the left hemisphere) shows a dominance for language processing, indicating left-hemisphere specialization. Differences in performance between ears help identify functional asymmetries in the brain.
- this is because the auditory system is not completely crossed (ipsilateral and contralateral) pathway from each ear), but crossed connections conduct more rapidly
Monaural presentation: both pathways are active
Dichotic presentation: ipsilateral pathway suppressed
results:
-L hemisphere is dominant for processing verbal sounds and
temporal structure of sounds (e.g. Morse code),
-R hemisphere for non-verbal, emotional and musical sounds
what is the difference between amonaural and a dichotic presentation?(behavioral asymmetries)
Monaural presentation: When sounds are presented to one ear only, both the ipsilateral (same side) and contralateral (opposite side) pathways are active, sending auditory information to both hemispheres of the brain.
Dichotic presentation: When different sounds are presented to each ear simultaneously, the contralateral pathways (which cross to the opposite hemisphere) dominate because they conduct more rapidly and efficiently. The ipsilateral pathways (which remain on the same side) are relatively suppressed in this scenario. This suppression helps isolate the processing of each ear’s input to primarily the opposite hemisphere, thus highlighting functional asymmetries in the brain.
what is teh Visual half field stimulation? (behavioral asymmetries)
-a technique used in neuroscience and psychology to study brain lateralization, particularly how each hemisphere processes visual information.
-L hemisphere is dominant for processing letters and words
-R hemisphere for complex spatial patterns and faces
what is a Somatosensory tests? (behavioral asymmetries)
-left hand (R hemisphere) dominant for processing
objects and spatial patterns (e.g. Braille)
-right hand (L hemisphere) for letters and temporal
patterns (e.g. dynamic Braille)
what are some observations task used for behavioral asymmetries?
-Right hand (L hemisphere) is dominant for verbal motor
tasks (e.g. crossword, gesturing during speech)
- Left hand for spatial motor tasks (e.g. drawing, puzzle)
- R half of the face (L hemisphere) opens more quickly
during facial movements for speech
- L half of the face (R hemisphere) displays stronger
emotional expression
-and interference tasks during multitasking (piano players):
- Non verbal vocalization (humming) can disrupt the L hand
- speaking can disrupt the right hand
what functions are not laterilized?
-Many elementary sensory and motor functions
-touch
-simple voluntary movement
what are the 2 laterization models?
Unilateral specialization models: each hemisphere has its own
functions and methods, performs these independently
– What essential element of a function? E.g. is L hemisphere
specialized in language or in fine temporal discrimination of
stimuli?
– Hemispheres may fundamentally differ in their method of
operating, e.g., directed at analysis (L) or synthesis (R)
- Interaction models: both hemispheres capable of performing all
cognitive functions, but are somewhat specialized
– Hemispheres simultaneously involved in different aspects of
the same task
– During normal functioning, one hemisphere inhibits activity of
other hemisphere; e.g., LH inhibits linguistic activities of RH
– Cerebral damage: intact hemisphere may take over functions
of damaged hemisphere (intact hemisphere no longer
inhibited by damaged one) as a manifestation of plasticity
– Individual differences in cognitive style/strategy
what can cause variations in asymmetry?
Handedness (ex.± 95% of right-handed and 70% of left-handed people have a L hemisphere dominance for language)
* Sex
* Environment
what affects can handneness have on asymmetry?
-± 95% of right-handed and 70% of left-handed people
have a L hemisphere dominance for language
-Anatomical asymmetries more
pronounced in right-handed persons
-Left-handers: more within-group variance in
speech lateralization (30% R or bilateral)
-Anatomical L-R differences more related to locus of language than actual handednes
-Larger corpus callosum in some left handers= actually related to degree of lateralization
how can sex affend asymmetry?
testosterone:
-higher prenatal testosterone levels are associated with more male-typical play behavior in children
Estrogen:
fluctuation menstrual cycle dendritic spines
male
-larger medial frontal areas
.larger cingulate areas
-larger amygdala and hypothalamus
-larger white matter volume
-more neurons
-larger brain
etc….
female:
larger language areas
greater relaitve amount of gray matter
more densly packed neurons in temporal lobe
more giri
-thicker cortex
etc…
fMRI:
-Some recent machine learning results: possible to
classify sex based on resting state fMRI (75%
correct) and cortical morphology (96% correct)
- Men show more asymmetry (esp verbal tasks)
- Males show more intrahemispheric(same hemisphere) connections,
females more interhemispheric connections
how does the environment effect brain asymmetry?
Different languages (e.g. Chinese, more prosody) give slight changes in cerebral organization
Sensory deprivation gives rewiring
- Deaf: auditory cortex reduced WM volume, increased GM cerebellum
- Blind: auditory input and echolocation to visual cortex
Environmental deprivation
- Romanian orphans 20% smaller brain (adopted before 18 months: normal)
- SES related to poorer language skills and brain language-related networks
what sre some asymmetries in the temporal function?
-left:Dominance for analysis of speech
sounds and verbal memory (both
auditory and visual)
-Right temporal lobe
Dominance for analysis of musical
sounds and non-verbal memory (both
auditory and visual)
Might also be dominant for valence of
emotional expression (right lesions
lead to impairment of expression
recognition, whereas left lesions
generally do not)
Temporal lesions can lead to a broad range of dysfunctions:
- auditory and visual perception, language, long-term memory, personality
and emotion
- Bilateral lesions relatively larger effects
