The Neuroscience of Intelligence
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Social–economic status (SES), thought to be key by many intelligence researchers, may be confounded with intelligence on a neural level. Implications of this are provocative for public policy.
To the extent that different patterns of cognitive strengths and weaknesses are rooted more in neurobiology and genetics than in childhood experience, it is incorrect to blame lack of economic or educational success entirely on poor motivation, poor education, or other social factors.
Neuroscience progress offers exciting opportunities for intelligence researchers. It is a great time to enter the field.
Further Reading
Clocking the Mind: Mental chronometry and individual differences (Jensen, 2006). This is a technical manifesto that lays out the promise of chronometrics and the challenges of implementing it.
On intelligence (Hawkins & Blakeslee, 2004). This is a non-technical exploration of insights about how neuroscience can provide a blueprint for building intelligent machines.
“Creativity and intelligence: Brain networks that link and differentiate the expression of genius” (Jung & Haier, 2013). A summary of neuroimaging studies of intelligence and creativity that proposes how genius may emerge from specific brain networks.
“DREADDs (designer receptors exclusively activated by designer drugs): Chemogenetic tools with therapeutic utility” (Urban & Roth, 2015). This is a highly technical neuroscience explanation of the topic.
“Functional connectome fingerprinting: Identifying individuals using patterns of brain connectivity” (Finn et al., 2015). This is an exciting study on using neuroimaging to create unique and stable patterns of brain connectivity that predict intelligence test scores. It’s highly technical, but take a look. This work may be the beginning of a new phase of intelligence research.
G is for genes: The impact of genetics on education and achievement (Asbury & Plomin, 2014). This is a highly readable, non-technical summary of genetic research on mental abilities. Specific policy recommendations for education reform are discussed.
Glossary
Allele.
One of the alternative forms of a gene that is located at a specific location on a specific chromosome.
Autism.
A complex neurodevelopment disorder with a range of various cognitive and behavioral symptoms often referred to as a spectrum of disorders.
Base pairs.
Building blocks formed by pairing adenine (A), guanine (G), cytosine (C), and thymine (T) that link the two strands of DNA like rungs on a ladder. There are an estimated 3 billion base pairs in human DNA.
Behavioral genetics.
The field of study that examines the role of genetic influences on behaviors and traits.
Behaviorism.
A psychology theory popular in the 1950s and 1960s that assumes a person is essentially passive, responding to environmental stimuli, and that overt behavior is the only thing that can be studied.
Bell curve.
Another name in statistics for any normal distribution of scores or traits. Also, the title of a provocative 1994 book about intelligence and society.
Blank slate.
A philosophical/psychological view that all traits in a person are formed mostly by nurture. Also, the title of a 2002 book that argues against this view based on modern science.
Bochumer Matrizen-Test (BOMAT).
A standardized intelligence test based on solving abstract reasoning problems often used as an estimate of the g-factor.
Brain-derived neurotrophic factor (BDNF).
A protein implicated in learning and several aspects of neuron health and development.
Brodmann areas.
A system for using numbers to define brain areas by anatomical location, originally based on autopsy studies of neuron structures (see Figure 3.6).
CAT scan.
Computerized axial tomography is a procedure that uses X-rays to image body tissues and structures. These images provide no information about the functioning of tissues.
Chemogenetics.
This is a technique used to experimentally turn neurons on and off using specially designed chemicals (see DREADD).
Chromosome.
Thread-like structure that carries DNA in genes. Humans have 23 pairs of chromosomes.
Chronometrics.
A method of measuring information processing speed in the brain while performing standard cognitive tasks. The measurements are made in units of time and therefore may provide a quantitative assessment of intelligence on a ratio scale.
Continuity hypothesis.
The idea that the genes related to high intelligence are the same as those related to low intelligence.
Correlation.
A way to describe how strongly two things are related to each other (see Figure 1.2).
CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats/Cas genes).
This is a method for editing the genome using bacteria.
Cross-sectional study.
A research study design that uses different subjects at different time points to establish a trend (see longitudinal study).
Cross-validation.
A key step of replicating a finding to be sure the finding also applies to an independent sample.
Crystallized intelligence (Gc).
The ability to learn facts and absorb information based on knowledge and experience.
Deep brain stimulation (DBS).
A neurosurgical procedure involving the implantation of a medical device called a neuro-stimulator that delivers controlled mild electrical shocks to targeted brain areas.
Default network.
The network of brain areas that is active while a person is not focused on any particular mental activity.
Designer receptors exclusively activated by designer drugs (DREADD).
A system for activating brain receptors using synthetic molecules.
Diffusion tensor imaging (DTI).
An MRI technique that uses water diffusion patterns to image white matter fibers.
Discontinuity hypothesis.
The idea that the genes related to high intelligence are different than those related to low intelligence.
Dizygotic (DZ) twins.
Fraternal twins; they have 50% of their genes in common.
DNA.
Deoxyribonucleic acid is the hereditary material in genes.
Doogie mice.
A strain of “smart” mice genetically engineered to solve mazes faster than controls.
Dopamine.
A neurotransmitter that helps control the reward and pleasure centers and also helps regulate cognition, movement, and emotional responses.
Double helix.
The structure formed by double-stranded molecules of DNA.
Edge.
Refers to the association of two brain areas in graph analyses of brain connectivity.
EEG.
An electroencephalogram measures the electrical activity of the brain by using electrodes attached to your scalp.
Elementary cognitive tasks (ECTs).
These are tasks that require basic mental processes like attention.
Epigenetics.
The field of study that investigates how genetic expression may be influenced by external factors.
Evoked potential.
A special application of EEG which records brain electrical activity that is induced by a specific stimulus like a light flash. The evoked potential is derived by averaging the EEG from the same stimulus repeated many times.
Factor analysis.
A statistical method that describes patterns of relationships among many variables based on correlations.
False positive.
A test result that erroneously indicates something that turns out to be untrue.
Fluid intelligence (Gf).
Refers to inductive and deductive reasoning for novel problem-solving. Fluid intelligence is closely associated with the g-factor.
Fluorescent proteins.
Light-emitting chemicals that can be used to visualize the internal workings of neurons.
Fluorodeoxyglucose (FDG).
A radioactive substance used in positron emission tomography (PET) to label metabolic activity.
Flynn effect.
Refers to the gradual generational increase in raw IQ scores. The causes are not established and whether the effect is on the g-factor is unsettled.
Fractional anisotropy (FA).
A measure of water diffusion derived from MRI and used to image white matter fibers and assess their integrity.
Frontal dis-inhibition model (F-DIM).
Based on neuroimaging studies of creativity, this framework suggests a system of brain areas that may be associated with creativity (see Figure 6.6).
Frontotemporal dementia (FTD).
A rare degenerating illness similar to Alzheimer’s disease characterized by progressive neuron loss especially in frontal lobes.
Full-scale IQ.
The total score based on summing all the subtest scores from a standardized intelligence test.
Functional MRI (fMRI).
A neuroimaging procedure using MRI that measures regional brain activity by detecting aspects of blood flow.
g-factor (g).
Denotes the general feature of intelligence common to all tests of mental abilities and estimated best from a battery of tests.
Gene.
A hereditary unit consisting of a DNA sequence at a specific location on a chromosome.
Gene expression.
The process by which genetic instructions start or stop creating proteins.
Generalist genes hypothesis.
The idea that the same genes affect most cognitive abilities rather than each cognitive ability is influenced by a different set of genes.
Genome.
The entire set of DNA base pairs. All the genetic material of an organism.
Genome-wide association study (GWAS).
A method that searches the genome for small variations (see single-nucleotide polymorphisms or SNPs) that occur more frequently in people with a particular disease or trait. Each study can look at hundreds or thousands of SNPs at the same time (see microarrays).
Genomic informatics.
The field of managing and understanding vast data sets of genetic information from individual base pairs to genomes.
Genomics.
The study of gene structure and function.
Graph analysis.
A mathematical tool that is used to model brain connectivity and infer networks of brain areas that are structurally or functionally associated.
Heritability.
A statistical estimate of how much variation in a trait or behavior in a population is due to genetic influences.
Hub.
The term used in graph analysis to denote a brain area with many connections to other areas.
Intelligence.
The ability to think and learn. The opposite of stupidity.
IQ.
Intelligence quotient. A measure of intelligence derived from a psychometric test, but it is defined differently depending on the test. IQ points are not measures of a quantity like distance or weight. IQ scores have meaning only relative to other people and are best understood in terms of percentiles.
Locus.
The position of a gene or genes on a specific region of a chromosome.
Longitudinal study.
A study where each subject is followed over time to investigate any changes (see contrast with cross-sectional study).
Magnetic resonance imaging (MRI).
A technique based on pulsing radio-wave energy through powerful magnetic fields to create detailed images of body tissue as water molecules react to the energy changes.
Magnetic resonance spectroscopy (MRS).
A specialized MRI technique used to measure biochemicals in the brain.
Magneto-encephalogram (MEG).
A technique for measuring localized brain activity based on detecting fluctuating magnetic fields that result from aggregate neuronal firings.
Meritocracy.
A system based on ability.
Methylation.
A chemical process that can change DNA. Of special interest in epigenetic investigations.
Microarray.
A tool used to determine whether the DNA from a particular individual contains a mutation in genes (SNPs). Thousands of SNPs can be studied simultaneously.
Mnemonic methods.
Techniques and strategies used to improve and augment memorization.
Molecular genetics.
A field of study that investigates how genes function in terms of chemistry and physics.
Monozygotic (MZ) twins.
Identical twins; they have 100% of their genes in common.
Mozart effect.
The claim that listening to classical music increases intelligence.
Neuro-g.
The concept that at least part of the general factor of intelligence has a specific basis in the brain (genetic or not).
Neuro-poverty.
The concept that one of the many causes of poverty may be related to the genetic basis of intelligence.
Neuro-SES (social–economic status).
The concept that part of the overlap between intelligence and SES may be due to genetic influences.
Non-shared environment.
Unique experiences that contribute to the environmental influences on heritability.
Optogenetics.
Methods for controlling brain function with light.
Parieto-frontal integration theory (PFIT).
A framework proposed in 2007 that identifies specific areas distributed across the brain relevant for general intelligence.
Performance IQ.
Non-verbal intelligence score derived from an IQ test.
Pleiotropy.
Occurs when one gene influences variability in two or more seemingly unrelated traits.
Polygenicity.
Occurs when many genes contribute to variance in a single trait.
Positive manifold.
Term used to describe the robust finding that tests of all mental abilities are related to each other in the same direction: as scores on one test increase, scores on the others tend to also increase.
Positron emission tomography (PET).
A technique to image body tissue functioning based on detecting the accumulation of low-level radioactive labels.
Proteomics.
The study of proteins and how they work.
Psychometrics.
A set of methods that uses various kinds of paper and pencil tests and statistical methods to study intelligence and personality.
Quantitative genetics.
The study of genetic influences on variance of continuous traits (like intelligence or height) among individuals in a population.
Quantitative trait locus (QTL).
Refers to a region of DNA related to a trait like intelligence, as determined by statistical techniques.
Raven’s advanced progressive matrices (RAPM).
A difficult test of non-verbal abstract reasoning widely used to estimate the general factor of intelligence.
Region of interest (ROI).
A brain area defined for neuroimaging analysis.
Regression equation.
A general statistical method with many varieties for estimating the relationship among variables. Often used to predict one variable from a set of other variables weighted to maximize the accuracy of prediction.
Restriction of range.
A statistical problem referring to a lack of sufficient variance on a variable (like intelligence) for determining whether that variance is related to another variable.
SAT (scholastic assessment test).
A standardized test often used for college admission in the USA.
Savant.
A person of unusual ability or having profoundly detailed kn
owledge in a specialized or narrow topic.
Shared environment.
Common experiences that contribute to the environmental influences on heritability.
Single-nucleotide polymorphisms (SNPs).
A change or variation in a base pair substituting one base for another. SNPs may be associated with traits or diseases and can be hints for identifying relevant genes.
Social–economic status (SES).
A measure that combines education and income in various ways to estimate social class for use in studies about how these variables may influence behavior or traits.
Standard deviation.
A statistical measure that describes variation around the mean of a distribution of scores.
STEM.
Abbreviation for the fields of Science, Technology, Engineering, and Math.
Structural MRI (sMRI).
An MRI technique that visualizes the makeup of tissue but contains no functional information.