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Intelligence and Cognitive Functioning 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 processes. • 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 Intelligence • 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 Intelligence What can we learn from Einstein’s brain? Einstein’s brain was about 200 gm lighter than average. 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 abilities. 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 Intelligence • General intelligence correlates with: o the volume of gray matter, particularly in the frontal areas; 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 (columns) The Biological Origins of Intelligence • • • 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 choices. Intelligence is also related to efficiency, made possible by: o enhanced myelination; o faster transfer from a limited short-term memory to long-term storage; o use of less energy while engaging in tasks. The Biological Origins of Intelligence Factor analysis has identified three clusters of specific abilities: linguistic, logical-mathematical, and spatial. Language involves structures in the left frontal and temporal lobes. Spatial ability depends on (right) parietal lobe structures. Mathematical performance engages two areas: Calculations and arithmetic facts involve the left frontal area. 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 Intelligence • • “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 similarity. • 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 Intelligence Hereditarians believe racial differences in IQ are genetic. 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 ancestry; social class and cultural factors are more important. An American Psychological Association task force concluded that the data do not support the hereditarian position. • The Biological Origins of Intelligence 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 Intelligence 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 effective. ◊ The Biological Origins of Intelligence 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 glutamate. Genetic manipulations with mice have improved some capabilities, but with uneven results. Deficiencies and Disorders of Intelligence • Although intelligence and cognitive abilities typically decline with age, the amount of loss has been overestimated. 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 Intelligence • Reduced speed is an important factor in performance loss. 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 action. • 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 Intelligence • 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 memory. o Administered in the form of dihydrotestosterone, it is aromatized to estrogen and improves verbal and working memory. Deficiencies and Disorders of Intelligence 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 Intelligence • Down syndrome o Down syndrome is usually caused by the presence of an extra 21st chromosome. o IQs are usually in the 40 to 55 range, though some individuals are less impaired. 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 fluid. • Half of hydrocephalics with 5% brain capacity have IQs over 100. • A Normal and a Hydrocephalic Brain Figure 13.14 Deficiencies and Disorders of Intelligence 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 10,000. Deficiencies and Disorders of Intelligence • 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 Intelligence • 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 delayed. 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 Intelligence • • 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 Intelligence 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 speech. 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 Intelligence 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. 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 Intelligence 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 formation. Deficiencies and Disorders of Intelligence 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 Intelligence 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 Intelligence 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 Intelligence • • 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 Intelligence • • 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.