Francis Galton and the study of Head/Brain Sizes
- Measured the heads of Cambridge University students
- Found that those 19yo with degrees had larger heads
- Assumed that head sizes had a correlation to intelligence
2005 Meta-Analysis on Brain Size
- Found there were small correlations between the brain size and IQ
- Supports the idea that individual differences in brain size may lead to individual differences in intelligence but the evidence is not strong
2015 Meta-Analysis on Brain Size
- Found an overall significant positive correlation between brain sizes and IQ scores
- Small correlation (smaller than 2005’s)
- Found evidence of publication bias (small and non-significant associations often omitted)
Is there a correlation between the number of brain cells, brain weight, and IQ?
(postmortem brains from Danish males)
- 50 postmortem brains from Danish males (20-52yo) for whom there was documentation of premorbid IQ
- IQ test from army
- Asked whether IQ correlated with the number of brain cells in the human neocortex or with brain weight?
- Found no correlation between IQ and no of brain cells
- Found weak correlation between IQ and brain weight
Brain Size/IQ Debate: Sex Differences
- On average, adult male brains have 10.8% total brain volume larger than women
- However there is also a clear absence of sex differences in IQ
- Hence, large brains do not necessarily translate to higher IQ in humans
Specific Brain Structures and their Link to Intelligence in Different Genders
in Men:
- Higher IQ correlates with more gray matter in posterior sensory integration areas
in Women:
- Higher IQ scores associated with more gray and white matter in frontal language areas
What do brain differences mean?
(Jugglers)
- Two groups of healthy young adults
- One of these groups had weekly juggling sessions for 6 weeks
- Found that there were white matter differences in the juggling group relative to non-jugglers
- These changes were in the region related to reaching and grasping in the periphery of vision
- Shows that there are changes in the white matter of the brain as a result of learning an entirely new skill
Navigation-related Structural Change in the Hippocampi of Taxi Drivers
- Individuals who successfully acquired the knowledge required of black cab drivers has larger posterior hippocampi
- The more time you spend as a London taxi driver, the more change you see in this region (increased volume)
- Recall that hippocampus plays a large role in memory, including spatial navigation
- ## One big difference between those who succeeded and failed was the amount of time spent training to acquire the spatial knowledge
Global Determinants of Navigation Ability (Sex Differences)
- Globally, men outperform women in spatial navigation and abilities
- When they account for both GDP (and the countries’ economic and political opportunities, wellbeing, education for women), they both significantly predict a country’s estimates
- More gender equality = Less gender differences in spatial abilities
- How they perform in spatial abilities correlate to academic performance?
2019 UK Biobank Study
- 44-81yo (M= 63)
- Looked at correlations between ‘g’ and brain volume, cortical thickness, white matter integrity and white matter intensities
- Showed that grey and white matter accounted for more than double the g variance in older p than in middle-age p
- Older age = 13.6% and Middle-age = 5.4%
Explain grey matter
Consists of neuronal cell bodies
Explain cortical thickness
The thickness of the brain’s grey matter
Explain white matter
The connecting network of axons (or ‘wires) in the brain
Explain white matter integrity
A measure of the health of the white matter connections
Explain white matter hyperintensities
Scars in the brain’s connections
Neural Efficiency Theory
- Argues that intelligence is linked to more efficient use of the cortex
Study on Neural Efficiency
- Argues that people who have higher IQ require less brain activity to perform a task
- A PET study
- Inverse correlation between glucose metabolism in the brains of individuals who scored higher on the Ravens matrices
- Later did another study on cerebral metabolism
- Complex visual spatial task (tetris)
- After learning tetris, there was an overall decrease in cerebral metabolism (larger decrease in those with higher IQs)
Brain Efficiency, SAT Scores and Sex Differences
- Male and female participants with half high SAT scores and half average SAT scores
- During the PET scan, each participant completed a new SAT test
Male:
- Significant correlations between the math scores and glucose metabolism in the temporal lobes bilaterally
Female:
- No correlations
How Fronto-Parietal Grey Matter and White Matter Efficiency Differentially Predict Intelligence in Males and Females
- Male and female young adults were asked to perform various subsets of intelligence scales
- Looked at the structural differences - some measures of white matter efficiency
- Found that there was a link between white matter efficiency and intelligence
Male:
- No correlation between white matter efficiency differences and IQ
- Significant positive relationship between fronto-parietal grey matter volumes and intelligence
Female:
- Positive correlation between white matter efficiency differences and IQ
- Total grey matter volume did predict intelligence BUT a regionally specific contribution of the fronto-parietal grey matter was not evident
fMRI Study on Nature Neuroscience
- 6 imaging sessions/participant (mixture of rest and complex cognitive tasks
- Explored functional connectivity patterns (across the whole brain and within 10 key networks); Looked to see whether they were stable in performing each of the different tasks and in rest
- Found stability over the conditions; Connectivity patterns in frontoparietal network were UNIQUE to the individuals; Connectivity profiles appeared to predict levels of fluid intelligence
Explain fluid intelligence
- The figuring out component of intelligence
- Perceptual reasoning, Working memory, Processing speed
Explain crystallised intelligence
- More to do with the outcome of figuring something out
- Verbal comprehension
Explain Connectotyping
- Describes the distinct pattern of brain activity that characterises the way each person’s mind works
- Implies that mental processes do not necessarily enlist identical neural pathways in every person
Where would we find much of the variation relating to connectotypes of the brain?
- Tends to occur within the brain’s most sophisticated networks
- i.e. In the higher order control regions in frontal and parietal cortices
