Neurological Variations In Groups Of Healthy Individuals

Question 1

Factors contributing to neurological variances

Answer 1

• urbanicity impact
• sexual dimorphism and menstrual cycle
• handedness
• gender and transgender

Question 2

Rural vs urban upbringing

Answer 2

• (exclusively) rural-raised adolescents showed greater grey matter volume (GMV) in the left hippocampal formation
• rural-raised adolescents outperform urban-raised peers on tasks that involve spatial processing (eg Block design task in Wechsler IQ scale)
• hippocampal formation mediates the relationship between upbringing and Block design performance
  –> suggests link between enivronment, brain structure and spatial processing skills

Question 3

Types of handedness

Answer 3

~ 90% right-handed
~ 10% left-handed
~ 1% ambidextrous

left-handedness
- slightly more common in men than women
- more commonly found in individuals with neurodevelopmental and psychiatric conditions (intellectual disabilities, autism, schizophrenia)
- corresponds to right-hemisphere dominance for motor control

hand motor control
- primary regulated by contralateral hemisphere
- corresponds to left-hemisphere dominance for motor control

Question 4

Language and handedness

Answer 4

left hemisphere dominance in language
- dates back to research of Broca and Wernicke
- confirmed by Wada, fMRI, PET, ECoG, dichotic listening

no direct link between handedness and language lateralisation
- over 50% of left-handers have left-hemisphere dominance for language –> similar to right handers
- nearly 70% of left-handers are (in general) left-hemisphere dominant
- remaining left-handers are roughly split between bilateral and right-hemisphere language dominance

Question 5

differences in functional symmetry by handedness

Answer 5

• left-handed participants have significantly lower LIs than the right-handers for all four asymmetries tested

verbal fluency
- in general more left hemispheric
- left-handers a little less than right-handers

faces
- in general right hemispheric
- left-handers (-0.4) quite a lot less than righthanders (-0.6)

bodies
- in general rather right hemispheric
- left-handers (-0.4) less than right-handers (-0.5)

scenes
- in general rather right hemispheric
- left-handers (-0.3) less than right-handers (-0.4)

Question 6

Hormonal influence on neuroplasticity

Answer 6

sexual dimorphism
- clear and consistent physical differences between females and males of the same species

females
- hormone level fluctuate dynamically (huge spikes in progesterone and estradiol) during menstrual cycle –> influences brain plasticity (especially in hippocampal region)

Question 7

Hormonal influence on neuroplasticity: implications

Answer 7

understanind hormone fluctuations and brain structural plasticity
implications
1. design better treatments for cognitive and emotional challenges during a woman’s life
2. consider specific phases of the menstrual cycle in research (+ other hormonal states like contraceptive use, pregnancy, menopause)
3. roles of ovarian hormones in brain aging and diseases –> prevention, treatment and support (eg Hormone Replacement Therapy)

Question 8

Gender and Transgender

Answer 8

sexual brain differentiation
- is temporally differentiated from sexual differentiation of the genitals –> starting during second trimester

brain structures in transgender individuals
- often align more closely with their gender identity than their assigned sex at birth

Implications for brain differences in sex/gender
1. transgender research challenges traditional notions thath ‘male’ and ‘female’ brains are distinct based on sex assigned at birth
2. findings suggest that gender identity has a neurobiological component –> exists independently of the sex assigned at birth, rather reflects identity and experience
3. move beyond sex-based categorisations toward gender-sensitive research
4. include more diverse gender identities in studies