Chapter 12: Individual Differences in Cerebral Organization Flashcards
What is different about London taxi drivers
- they have increased area in L and R hemisphere of hippocampus but anteriorly decreased
- longer they have been a taxi driver in london the bigger their posterior hippocampus area
What is the function of the posterior hippoampus?
- memory and spatial navigation
What is the function of the anterior hippocampus?
- anxiety-related behaviours
Why do we drive on the right side of the road compared to the left
- A: In Europe, driving on the left may have originated from the romans who would steer and chariots with the left hand, to free up the right so they could use weapons to defend against enemy attacks.
This carried over into medieval Europe and in 1773, the British government passed measures to make left-hand traffic the law.
-In the US, right-hand traffic goes back to the 18th century. Freight wagons were pulled by teams of horses. and the drivers rode on the left rear horse, using their right hand to more easily control the team. Traffic shifted to the right so drivers could easily avoid collisions
What is Handedness associated with ?
- cerebral asymmetry and lateralization of the brain
- also associated with differences with cerebral blood flow, anatomical asymmetries and lateralization of functions like language
Familial vs nonfamilial left-handers
- familial left handers tend to be the ones with language in the right hemisphere or no asymmetry (both hemispheres)
- nonfamilial left handers look like right handers
When does hand preference appear by
about 10 weeks of fetal development
- 75% of fetuses show r handed preference and 90% of fetuses prefer right thumb sucking
- most people are right handed
- 90% of population is right handed in terms of writing
- 70-90% are right handed when judged more broadly
What did Jurgan Germanns study in 2019 find about left vs right handers
- difference in the size of the motor cortical hand area
- it was larger in the left hemisphere for right handers and larger in the right hemisphere for left handers
- they specifically looked at the hand-knob region in the brain
What did Graham Ratcliff find about anatomical asymmetry
- anatomical asymmetry in the population was related to speech production and not necessarily handedness
- aka. if speech was in the LH there was more anatomical difference
What are the four categories of theories for left handed vs right handedness
- environmental
- anatomical
- hormonal
- genetic
What percent of the population Is left handed
10%
What three subcategories do environmental theories break down into
- Utility: mothers are more likely to hold infant in the left hand so they are closer to the mothers heart and so the mothers right hand is free to do other tasks
- Reinforcement: for centuries children have been taught to write with their right hand, but modern education is not accepting left handedness (prevalence has not gone up)
- Damage: there may be some genetic bias toward being right handed. suggesting that being left handed is the result of a genetic anomaly or stressful in-utero development
(ex. 18% of twins are left handed which is close to twice that of regular population 10%)
What is different about male right-handers
they have significantly deeper fissure on the left than on the right
- there is no difference seen for left-handers
What are the two subcategories for the anatomical theories of handedness?
- enhanced maturation: the LH generally shows enhanced maturation and greater development which may influence handedness
- Those seen in nature:
- this theory points out that the heart is on the left side of the chest, the temporal lobe is larger on the left, and the areas that influence birdsong are found in the LH of brain
- LH dominance for language and motor control may just be another manifestation of this trend
(the research on these theories is little to none)
what are the hormonal theories of handedness
- exposure to different levels of testosterone early in life could impact cerebral organization and asymmetry
- testosterone is generally inhibitory on development
- testosterone acts on the LH of the brain leading to great development of the RH and Left handedness in some individuals
STUDIES EXAMINING AMNIOTIC FLIUD HAVE NOT SUPPORTED THIS THOERY
What are the genetic theories of handedness
there could be a dominant gene for handedness
- a more widely researched variant suggests the dominant gene encodes left hemisphere speech ( if there was a r handed gene it would also encode LH speech
- Genes that favour left hemisphere speech also favour an advantage in motor control of the right hand
Explain dominant and recessive genes linked to handedness
- the dominant form of the gene favours LH specialization
- the recessive form confers no preference
- people with 2 copies of the recessive gene divide evenly between left and right hemisphere specialization
- this model suggests that 12.5% of the population would be left handed which is pretty close to the actual average of 10%
- no genes identified to be associated with such lateralization
Sex differences in concussion studies
- men more mild concussions
- females appear to account for more injuries, higher rates of concussions in basketball, soccer, soft/ball baseball, swimming.
- though this could be due tot the fact that females tend to report more injuries and seek medical care more often then males
What are the sex differences in Symptomatology
women- affective and cognitive
men- more motor deficits
Why do sex differences appear in children
- it is often argued that sex differences between boys and girls are only there because we socialize them differently
- which is likely not completely true, lots of evidence against this
- evidence against this?
1. women being more fluent using language and men tend to be better in spatial analysis
Are the differences between or within sex bigger
- individual differences within sexes are larger than the overall sex difference
What is the biggest sex difference seen in children
- play behaviours
- children spend most of their time in play, and play is critical for brain development
- differences are often seen in playmate choice, toy preference, and activities
What do developmental studies show us about testosterone and toy and play preferences
- developmental studies show that early testosterone exposure influences toy choices and play behaviours
- by 7 weeks gestation the testes begin to produce testosterone. leading to higher levels in males
what is prenatal testosterone exposure associated with ?
- prenatal testosterone has NOT been actually associated with handedness
- but it has been linked to play behaviour in children
- increased testosterone during pregnancy has been linked to increases in male-type play behaviour
- this has also been shown in monkey’s which shows that these sex differences, it can not all be due to socialization
Why are males more attracted to trucks and toy cars
- not known
- could be as simple as they are able to be moved in space whereas females perfect tactile stimulation
What does effect size mean
- how big the difference is between the means of two groups
- significant or not
What are the 5 classes of cognitive behaviours Kimmura examined
- motor skills
- spatial analysis
- mathematical aptitude
- perception
- verbal abilities
What are the tasks favouring women
- mathematical calculation
- verbal memory (recall)
- object memory (where this are)
- fine motor skills, coordination
- perception (rapidly matching)
What are the tasks favouring men
- mathematical reasoning
- geometric form perception
- mental rotation
- target-directed motor skills
- visual imaging
Sex differences in motor skills
- men are superior at target throwing and catching
- females have superior fine motor skills such as the peg board
- differences present early in like, as young as 3
Sex differences in spatial analysis
Men
- generally better at spatial tasks requiring mental rotation and navigation
- generally quicker at learning spatial navigation tasks
Women
- improve on mental rotation tasks when block figures are replaced by human shapes in different postures
- the human figure rotation task
- women better at identifying which objects have been moved or displaced, better recall for landmarks
the sex differences in spatial ability tasks is not in spatial information its the difference related to what you do with the info
What is the table top map for?
- route learning
- men learn new routes in fewer trials than women do but women recall more landmarks along the way
Sex differences in mathematical Aptitude
Men - mathematical reasoning Females - computation - much better at reading (3x more than that of men in math)
What happens to sex differences seen in mathematical aptitude as we age
- Gap closes as we age, in 7th grade males out number females in math 13:1
- by adolescence its 4:1 and remains stable
When girls do well in math, what else do they generally do well in
- language
- this can not be said for boys
What does the textbook argue about sex differences in STEM
- they argue that this difference in women in STEM is due to women choosing careers that utilize their cognitive strengths
aka math and language
What is the Sunshine list
- the alberta government requires that any individual whos salary is supported by tax payers (all university employees in canada) must be publicly disclosed if it is over 125k
- your name, position, salary, non-salary benefits, and severance must be made public every year
Sex differences on perceptual tests
Women
- more sensitive to sensory information other than vision
- more sensitive to facial expressions and body postures
- women have lower thresholds to detect sensory stimuli
- women detect sensory stimuli more quickly than men do
Sex differences in verbal ability
Women
- verbal fluency
- verbal memory
- partly because girls start talking before boys and appear to be more fluent throughout life
Sex differences in brain structure that favour women
- larger language areas
- larger medial paralimbic areas
- larger lateral frontal areas
- greater relative amount of gray matter
- more densely packed neurons in temporal lobe
- more gyri
- thicker cortex
Sex differences in brain structure that favour men
- larger medial frontal areas
- larger cingulate areas
- larger amygdala and hypothalamus
- larger overall white matter volume
- larger cerebral ventricles
- larger right planum parietale
- more neurons overall
- larger brain
What are the influences of sex hormones on brain structure
- differences in the distribution of estrogen and androgen receptors during development could affect brain structure
- there are sexually dimorphic regions of the brain in the prefrontal cortex, the paralimbic cortex and the posterior parietal cortex
What are the sex differences in brain volume relative to cerebral size
Women
- prefrontal and medial paralimbic regions brain volume significantly higher in women
- estrogen receptors during development
Men
- larger relative volumes in the medial and orbital frontal cortex and the angular gyrus
- androgen receptors during development
Sex differences in concentration of gray matter
- males have uniform concentration of gray matter but females have some areas of high and low concentration
What are the symmetrical differences between sexes
- women brain more symmetrical than mens
- the asymmetry of the planum temporal and sylvian fissure is more common in men which supports the differences associated with language related structures
- women have more inter-hemispheric connections
What are the language structures that lay close to the sylvian fissure
- Broca’s
- Wernicke’s
- Auditory cortex
Can you differentiate between a male and female brain by looking at them
no
- but by the patterns of connections between brain regions found in resting-state fMRI are reliable predictors
- males show greater connectivity in RH
- females LH
How to study brain connections and what are the sex differences in brain connections
- diffusion tensor imaging
shows females have greater inter-hemispheric connectivity and males have greater intra-hemispheric connectivity (within)
What does sexual orientation mean
- individual attraction to a specific gender
when does gender identity mean
- relationships between biological gender, internal sense of self and external gender behaviours
Sexual Orientation and cerebral asymmetry
- homosexual men throw less accurately than heterosexual men but homosexual women throw more accurately than heterosexual women
- homosexual men best in verbal fluency and homosexual women worst
Brain activation related to sexual preferences
safron fmri study
- region of interest was ventral striatum
- there are differences in activity in the ventral striatum reflecting sexual preferences for heterosexual and homosexual men but not bisexual men
- homosexual men showed male over female preference and vice versa
What is the ventral striatum associated with
- desire, craving, wanting , includes food and sex
What are the thee explanations that contribute to cerebral asymmetry
- language and culture
- congenital deafness
- environmental deprivation
Language and cultures contribution to cerebral asymmetry
- believed that languages like Chinese that have more prosody (remember rhythmic pattern) and reading involves characters/pics rather than words would be less left hemispheric (and more right hemispheric), but this is not the case.
- bilinguals have larger language zones
what is Diffusion Tensor Imaging
- DTI detects the directional movements of water molecules to create virtual images of the brains nerve fibre pathways
What is Frictional Ansiotrophy
- DTI measure
- measure white matter tracts
- scale of 0 to 1 and lower values indicate worse integrity (water not moving in the same direction)
Frictional Ansiotrophy in Bilinguals
- Although the research is not clear with some studies displaying increased FA, decreased FA, and both.
- when you age the number of white matter tracts decrease and their ability to move as quickly across white matter tracts decreases
What is Congenital Deafness
- if you don’t have exposure to verbal language, do you still see cerebral lateralization (generally thought to be linked to language).
- Some studies have found that congenitally deaf individuals do not show the right visual field superiority on tachiscopes, suggesting that lateralization is abolished if there is no exposure to language.
- However lesion studies say the opposite, congenitally deaf individuals with lesions in the left hemisphere perform poorly on language tasks, while patients with right hemisphere damage performed poorly on spatial tasks.
In blind individuals, what happens to the visual cortex
- the visual cortex is recruited to participate in nonvisual tasks such as hearing, touch, and olfaction
Temporal-lobe visual areas are repurposed for hearing, with some blind people creating a sound map of the environment to support echolocation
Hearing in the visual cortex
- MRI-derived maps for echo sounds in the primary “visual” cortex of blind expert echolocators.
- Blind people are learning to navigate the world using echolocation!!
- It appears that these blind participants have significant reorganization of the visual cortex to aid in their echolocation.
Studies on orphan raised in deprived environments showed what
- long lasting impacts on brain structure and function
-Children adopted into enriched environment around age 2 - At age 12, their brains remained approximately 20% smaller than age-matched control and included impoverished gray and white matter
Significant behavioural and cognitive problems into adulthood
SES and cortical surface area
- Socioeconomic status (SES) quantifies income, education, and occupation
SES is related to cortical surface area in the frontal, parietal, and temporal lobes
-Noble and colleagues (2015) associated family income with cortical surface area. Area brain regions shown in red were significantly smaller in children from low-SES families.
