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Intelligence and Cognitive
Chapter 13
The nature of intelligence
The biological origins of intelligence
Deficiencies and disorders of intelligence
The Nature of Intelligence
 Intelligence is the ability to reason, to understand,
and to profit from experience.
 The measure of intelligence is typically expressed as the
intelligence quotient (IQ).
 What do intelligence tests measure and predict?
o Scores are highly correlated with:
• school performance;
• job performance;
• income;
• socioeconomic level.
The Nature of Intelligence
o A criticism is that intelligence tests don’t assess
“practical intelligence”—abilities that show up in
practice but not on tests.
o Standard tests are highly influenced by culture. Some
tests, such as the Raven Progressive Matrices, attempt
to remedy this.
o Intelligence may not be a real entity, but an
abstraction invented to describe a group of
• If so, we should not expect intelligence to be
defined by a single structure or a discrete network
of structures.
The Nature of Intelligence
 A critical question for a biological understanding of
intelligence is whether intelligence is a single capability
or a collection of several independent abilities.
 Intelligence theorists tend to fall into one of two groups,
lumpers or splitters.
 Lumpers claim that intelligence is a single, unitary
capability, which is usually called the general factor, or
simply g.
 Splitters hold that intelligence is made up of several mental
abilities that are more or less independent of each other.
The Biological Origins of
• Brain size itself does not determine intelligence.
• What is more important is the ratio of the brain’s size to
body size.
o The ratio for humans is one of the highest.
o The ratio for males is slightly higher than for females.
• Perhaps women’s brains are more efficient, having
a higher ratio of gray to white matter.
• Perhaps males’ brains are larger because their
spatial ability requires greater brain capacity.
 Among humans, brain size accounts for 11% of the
variation in intelligence.
The Biological Origins of
 What can we learn from Einstein’s brain?
 Einstein’s brain was about 200 gm lighter than
 His brain did not contain more neurons than average.
 He might have had a higher ratio of glial cells to
neurons in the left parietal lobe.
 Differences in specific areas may relate to special
His parietal lobes were larger.
The parietal lobes are important in mathematical
ability and visual-spatial processing.
 But, were these differences cause or result?
Albert Einstein and His Brain
Figure 13.3
The Biological Origins of
• General intelligence correlates with:
o the volume of gray matter, particularly in the frontal
o and the volume of white matter.
• More important than size is how the brain is organized.
• Brains from people with high IQs are characterized by:
o a thicker cortex;
o smaller and more tightly packed processing modules
The Biological Origins of
IQ scores are correlated with reaction time and even more so with
nerve conduction velocity.
People who are more intelligent excel on tasks in which stimuli are
presented for an extremely short interval and on tasks that require
Intelligence is also related to efficiency, made possible by:
o enhanced myelination;
o faster transfer from a limited short-term memory to long-term
o use of less energy while engaging in tasks.
The Biological Origins of
 Factor analysis has identified three clusters of specific abilities:
linguistic, logical-mathematical, and spatial.
 Language involves structures in the left frontal and temporal
 Spatial ability depends on (right) parietal lobe structures.
 Mathematical performance engages two areas:
 Calculations and arithmetic facts involve the left frontal
 Estimation and use of visual-spatial representation involve
the parietal lobes.
 In many mathematic tasks, both areas are active.
Brain Locations for Math Calculation
Figure 13.8
The Biological Origins of
“Intelligent” behavior has been observed in animals such as
dolphins, chimps, birds, and even termites.
Tool use is one of the most dramatic examples.
o Chimps use twigs to extract termites from their mounds.
o Crows use twigs to fish for grubs, and can use a short stick to
obtain a longer stick that can be used to extract food from a
deep hole.
o Burrowing owls place animal dung around their burrows to lure
beetles for their “dinner”.
o The chimp Santino cleverly extracted stones from a concrete
wall and hid them to throw at spectators later.
Tool-Using Chimp
The Biological Origins of Intelligence
Intelligence has a heritability of around 50%, and concordances increase with genetic
Individual functions are heritable, including working memory, processing speed, choice
reaction time.
Heritabilities of neural components of intelligence:
brain volume: 90%; white matter: 88%; gray matter: 82%
Genes implicated in intelligence include:
o ASPS gene, a major determinant of brain size;
 PACAP precursor gene, which plays a role in neural signaling and neurogenesis.
 There are at least 150 candidate genes.
The Biological Origins of
 Hereditarians believe racial differences in IQ are
 They point out that racial differences are consistent
worldwide, and claim they correspond to brain size.
 Others counter that
 test performance does not vary with degree of African
 social class and cultural factors are more important.
 An American Psychological Association task force
concluded that the data do not support the hereditarian
The Biological Origins of
Environmental influences are difficult to determine.
 They are weak and often confounded with heredity.
 However, a study that controlled for confounding variables found that national
average IQ is correlated -0.76 with the incidence of infectious disease.
o Adoption studies help distinguish genetic from environmental influences.
• Children adopted from impoverished homes into middle class homes
increase as much as 16 IQ points.
• Yet, the children’s IQs are more highly correlated with the intelligence of
their biological parents than their adoptive parents, and this effect
increases over time.
The Biological Origins of
 Intervention studies also control confounding.
 The Head Start program
 produced initial IQ gains, which were not maintained;
 but produced long-term benefits in mathematics,
educational attainment, and career accomplishments.
 The Abecedarian Project, which began interventions at
birth, achieved long-lasting gains in IQ.
 A new early Head Start program starts at birth, in
recognition that intervention must occur early to be
The Biological Origins of
 Can intelligence be altered or enhanced?
 Nature poll found that 20% of respondents had used drugs to
enhance their concentration or memory.
 “Smart drugs” in use now include:
 Modafinil and methylphenidate for alertness, learning
 Dopamine agonists (amphetamine) for working memory
 Guanfacine for planning and spatial memory
 In development are ampakines that act on AMPA receptors for
 Genetic manipulations with mice have improved some
capabilities, but with uneven results.
Deficiencies and Disorders of
• Although intelligence and cognitive abilities typically
decline with age, the amount of loss has been
o Part of the reason is that older people are not
necessarily motivated to perform tasks such as
memorizing words.
o When the elderly are tested on the content of
meaningful material such as television shows and
conversations, the decline is moderate.
o Also, earlier studies were cross-sectional, confounding
results with the Flynn effect; a 35-year longitudinal study
showed less decline.
Deficiencies and Disorders of
• Reduced speed is an important factor in performance
o Speed of processing accounts for 99% of age-related
differences in working memory.
• Aging brings about a loss of coordination in the default
mode network, thought to represent preparedness for
• Losses can be minimized through practice, diet,
improved self esteem and, possibly, increased GABA.
• Those who maintain performance recruit additional brain
areas during tasks.
Compensation in Elderly Performance
Figure 13.12
Young and low-performing elderly subjects used the right frontal lobe in a
memory task; high-performing elderly subjects used both frontal areas.
Deficiencies and Disorders of
• The sex hormones provide some protection against the
effects of aging.
o Menopausal women can improve memory and
decrease Alzheimer’s disease risk via use of estrogen.
o Estrogen is associated with brain excitability,
metabolism, and blood flow, as well as responsiveness
to acetylcholine.
o In men, testosterone replacement improves spatial
o Administered in the form of dihydrotestosterone, it is
aromatized to estrogen and improves verbal and
working memory.
Deficiencies and Disorders of
 Intellectual disability is a limitation in intellectual
functioning and in adaptive behavior originating before
the age of 18.
 The criteria for intellectual disability are an IQ below 70
and difficulty meeting routine needs like self-care.
 This definition and the categories of disability are
arbitrary and likely to change in the future.
 Most cases of disability are due to a combination of
genetic and environmental causes.
 Environmental causes include disease during infancy,
prenatal exposure to viruses, and maternal alcoholism.
Categories of Intellectual Disability
Table 13.1
Deficiencies and Disorders of
Down syndrome
o Down syndrome is usually caused by the presence of an extra 21st
o IQs are usually in the 40 to 55 range, though some individuals are less
o Down is the leading genetic cause of intellectual disability.
o The glial cells secrete less of two proteins that support neuron survival.
o Evidence with mice suggests that increasing these proteins in women
carrying a Down syndrome fetus could be an effective treatment.
Deficiencies and Disorders of Intelligence
Fragile X syndrome is due to a mutated FMRI gene.
o This gene may be important in pruning excess synapses.
 The disorder is more likely in males and milder in females.
• PKU or phenylketonuria is caused by an enzyme deficiency,
leading to excess phenylalanine.
o Avoidance of foods high in phenylalanine can prevent
severe to profound intellectual impairment.
o Hydrocephalus is caused by a buildup of fluid in the
ventricles, reducing the amount of brain tissue.
• This can be treated by using a shunt to drain excess
• Half of hydrocephalics with 5% brain capacity have IQs
over 100.
A Normal and a Hydrocephalic Brain
Figure 13.14
Deficiencies and Disorders of
 Autism
 Autism is characterized by compulsive, ritualistic behavior,
impaired sociability, and mental retardation.
o It is one of five autism spectrum disorders.
• In Asperger’s syndrome, language and cognitive skills are
more normal.
o Autism has risen from 5 per 10,000 to 10-20 per 10,000.
• The increase may be due to changing criteria, earlier
detection, and increased willingness to make the diagnosis.
• However, autism could be on the rise, and experts are not
sure what the source of the increase is.
 Autism spectrum disorder has been consistent at around 60 per
Deficiencies and Disorders of
Symptoms of Autism
o About 80% have intellectual disability.
o They are mute or delayed in language development,
and they have trouble understanding verbal and
nonverbal communication.
o Verbalization often involves repetition, or echolalia.
o They are impaired in imagination; make-believe is
difficult and language is very literal.
o Their interaction with others is often limited to requests for
things they want; people may be treated as objects.
Deficiencies and Disorders of
Some researchers believe that the autistic individual lacks a
theory of mind.
o This is the ability to attribute mental states to oneself and to
others; the autistic person cannot infer what others are
thinking and appears to lack empathy.
 Researchers suggest that impaired mirror neuron activity
reduces the autistic person’s ability to empathize and to
learn language through imitation.
o Studies indicate weakness in the dorsal stream
connections that provide input to the inferior frontal cortex
and motor cortex.
• During imitation, transmission over the dorsal stream is
Deficiencies and Disorders of Intelligence
 The term savant is usually used to describe individuals who
have one or more remarkable skills but whose overall
functioning is below normal.
 Half of these individuals are autistic savants.
 There is some support for the idea that lower levels of
processing are freed from executive constraint.
 Temple Grandin is a high-functioning autistic.
 She earned a doctorate, teaches animal science, and
lectures on her expertise and autism.
 But her theory of mind is poorly developed and she is
baffled by social relationships.
Deficiencies and Disorders of Intelligence
• Early theories of autism attributed the disorder to a
psychological cause, such as lack of maternal
bonding or a disastrous experience of rejection.
• Now autism is viewed as a brain disorder.
o Subtle but widespread brain anomalies have
been found, especially in the brain stem, the
cerebellum, and the temporal lobes.
o However, the brain anomalies vary from
individual to individual, so there must be multiple
paths to the disorder.
Deficiencies and Disorders of
Brain development shows rapid frontal and temporal growth
until the age of 3 to 5.
o Although larger, these areas are underactivated during
tasks that should engage them.
o Some of these areas are actually undersized in adulthood,
suggesting there is a later period of degeneration.
Areas or systems with abnormal function include:
o the fusiform face area, important for identifying faces;
o the mirror neuron system;
o the default mode network, which shows lack of functional
connectivity (reduced white matter, synaptic weakness).
Decreased White Matter in Autism
Figure 13.18
Dark gray areas indicate decreased white matter.
Deficiencies and Disorders of
 Neurochemicals involved in autism include:
 Serotonin: A serotonin reuptake inhibitor and a serotonin
receptor blocker are useful for controlling repetitive
behavior and aggression.
 Glutamate antagonists improve social functioning and
reduce withdrawal, hyperactivity, and inappropriate
 Oxytocin, the “sociability molecule”
 Autistic children have decreased levels of oxytocin.
 Oxytocin reduces repetitive behavior in adults with
autism and Asperger’s, increases recognition of facial
expressions, and improves social cooperation and trust.
Deficiencies and Disorders of
 Environmental Factors in Autism
 Organophosphate pesticides have been linked to autism; they
inactivate acetylcholinesterase.
o Autism may result from an autoimmune reaction triggered by toxins or
maternal infections.
• Risk was increased in children whose mothers had rheumatoid
arthritis, celiac disease, and type 1 diabetes.
o Toxins that cause gene mutations (mutagens) appear to be linked to
 Autism has also been linked to deficiency in vitamin D (which is needed
for repairing DNA damage).
 There is no credible support for an effect of immunizations or the mercury
preservative used earlier.
Deficiencies and Disorders of
 Heredity and Autism.
 Siblings of autistics are 25 times more likely to be diagnosed
with autism compared to other children.
 Identical twin concordance is at least 60%; when individuals
with autistic-like symptoms are included, the rate increases
to 92%, compared to 10% in fraternal pairs.
 Autism is more common in males, suggesting X-linked genes,
but evidence for them is weak.
 Genes implicated in autism are involved in transmitter
activity, neuron development and migration, and synapse
Deficiencies and Disorders of
 Attention deficit hyperactivity disorder (ADHD) is
characterized by impulsiveness, inability to sustain
attention, learning difficulty, and hyperactivity.
 It is the most common childhood-onset behavioral disorder,
with an incidence of 3-5%
 However, some believe that ADHD is overdiagnosed and
children are unnecessarily medicated.
 As adults, ADHD individuals are prone to antisocial
personality disorder, criminal behavior, and drug abuse.
 Contrary to opinion, stimulant drug treatment may protect
individuals from later drug abuse.
ADHD Stimulant Treatment & Drug Abuse
Figure 13.20
Deficiencies and Disorders of
o Dopamine activity is reduced in the prefrontal
cortex and the striatum of individuals with ADHD.
• These structures are concerned with executive control,
impulse inhibition, working memory, movement,
learning, and reward.
 Most drugs that control symptoms are dopamine agonists,
such as Ritalin (methylphenidate).
 Those who do not respond to dopamine agonists
sometimes are helped by drugs that block norepinephrine
reuptake, such as modafinil and atomoxetine.
Deficiencies and Disorders of
 Brain Anomalies in ADHD
 ADHD is associated with reduced volume in the cerebral
hemispheres (particularly the right), the right caudate nucleus,
and the cerebellum.
 There is also evidence of reduced prefrontal and temporal
volumes and reduced white matter connections.
 Researchers argue that these brain changes result in
decreased connectivity in the default mode network and a
disruption of the attention-inhibition network.
• In support, control children activated a discrete network
during response restraint, but ADHD children inefficiently
activated much of the brain.
Deficiencies and Disorders of
ADHD clearly “runs in families”.
o Heritability averages 75% across studies.
o Identical twins have concordance rates of 79% compared
to 32% for fraternal twins.
Genes identified in ADHD
o Two dopamine receptor genes
o A dopamine transporter gene
o A serotonin receptor gene
o A serotonin transporter gene
o A gene affecting synaptic transmission
o LPHN3 gene involved in neural transmission and survival
Deficiencies and Disorders of
Many environmental contributors to ADHD are factors
affecting parents.
o ADHD has been correlated with maternal smoking and
stress during pregnancy, parental abuse of drugs, and
parental mood and anxiety disorders.
Other factors that are linked to ADHD include:
o brain injury, stroke, and birth complications;
o neurotoxins, such as lead;
o organophosphate pesticides;
o phthalates in perfume, shampoo, and cosmetics, which
may disrupt thyroid hormones during development.