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