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Objectives

Objectives. Identify the physical basis of behavioral traits in the brain. Discuss the difficult in analyzing behavioral traits and disorders Explain how genetics may be used to understand behavioral disorders

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Objectives

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  1. Objectives • Identify the physical basis of behavioral traits in the brain. • Discuss the difficult in analyzing behavioral traits and disorders • Explain how genetics may be used to understand behavioral disorders • Discuss the genetics and environmental influences on eating, sleep, intelligence, addiction, mood, schizophrenia and autism • Explain relations between some of them

  2. Genes and Behavior Behavior: • a continuum of emotions, moods, intelligence, and personality • occurs in response to environmental factors • how we respond has genetic underpinnings Behavioral genetics considers nervous system function and variation - Including mood and mind

  3. The Human Brain The human brain weighs about 3 pounds - Consists of neurons and supportive and nurturing cells called neuroglia Neurons communication: Synapses neurotransmitters Genes control the production and distribution of these chemical signals

  4. Neurotransmission Genes controlan la produccion y distri-bución de NT Sinapsis Neurotransmisores Canales Bombas MielinaEnzimas Figure 8.1

  5. Behavioral Genetics Uses empirical risk, twin studies, and adoption studies Association studies with SNPs and analysis of specific mutations that are present in individuals with the behavior Genetic studies of behavioral disorders are challenging traditional psychiatric classification - These disorders may lie on a continuum with many genes having input

  6. Porque es difícil analizar comportamientos: • Sintomas de diferentes síndromes se solapan • Participantes pueden dar información biased o sea prejuiciada • Se puede imitar comportamientos (hermanas con anorexia)

  7. Eating Disorders In the US, 5-10 million people have eating disorders - About 10% are male, both affected Twin studies reveal a heritability ranging from 0.5-0.8 Genes whose products control appetite or regulate certain neurotransmitters may predispose to eating disorders

  8. Eating Disorders Anorexia nervosa – Psychological perception of obesity and intentional starvation -Heredability 0.5-0.8 Bulimia – Psychological perception of obesity and intentional vomiting Muscle dysmorphia – Psychological perception of being too small

  9. Eating Disorders were always associated with females, risk estimates exclude males twin studies reveal a considerable genetic component: heredability 0.5-0.8 If they recurs in siblings, are difficult to interpret: its genetic or is imitation? Genes that encode proteins that control apetite , serotonin, dopamine (table 7.7) Four chromosomal regions with genes that are active in the part of the brain that regulates eating behavior

  10. Leptin and Associated Proteins Leptin is a protein hormone produced by fat cells - Acts on the brain to decrease appetite Ghrelin is a peptide hormone produced in the stomach - Responds to hunger by increasing appetite These and other hormones are important for general weight regulation

  11. Leptin and Associated Proteins Table 7.8

  12. Sleep Without sleep animals die Twin studies indicate 4 of the 5 stages of sleep have a hereditary component - The fifth stage, REM sleep, is associated with dreaming and so reflects input of experience more than genes

  13. Narcolepsy with Cataplexy Daytime sleepiness with tendency to rapidly fall asleep (narcolepsy) and periods of muscle weakness (cataplexy) • The genetic basis was first identified in dogs, then humans • Polygenic, requiring and environmental trigger • More common in certain families, suggest a genetic component • Hypocretin/orexin Figure 8.3

  14. Familial Advanced Sleep Phase Syndrome A disorder characterized by a very unusual sleep-wake cycle Affected members of a large family enabled researchers to identify the first “clock”gene in humans - circadian pacemaker: two clusters of neurons, express clock genes in response to light or dark stimuli - Theperiodgene enables a person to respond to day and night environmental cues

  15. Familial Advanced SleepPhase Syndrome A pedigree of the autosomal dominant form of the disease • 7:30pm fall asleep • 4:30 am awaken suddenly • period mutated in chromo 2 • Prevent a phosphorilation event Figure 8.4 Figure 8.4

  16. Intelligence A complex and variable trait subject to multiple genes, environmental influences, and intense subjectivity Refers to the ability to reason, learn, remember, synthesize, deduce, and create The IQ (intelligence quotient) test was first developed in France in 1904 - To predict academic success of developmentally disabled children

  17. The IQ Test Was later modified at Stanford University to assess white, middle-class Americans IQ is normally distributed around a mean of 100 ▪ Below 50 = Severe mental retardation ▪ 50-70 = Mild mental retardation ▪ 85-115 = Average intelligence ▪ Above 115 = Above average intelligence

  18. IQ has been a fairly accurate predictor of success in school and work • 100 is average • 66% of people 85-115 • 3% with intellectual disability • Low IQ predicts fairly well success in school and work • Low IQ also relates to poverty, divorce rate, failure to complete high school, incarceration, child out of wedlock • Opportunity = intelectual development Figure 8.5

  19. IQ tests verbal fluency, mathematical reasoning, memory, and spatial visualization ability The “g”value measures a general intelligence factor that represents the inherited portion of IQ The environment has less of an influence on IQ as a person ages High heritability Several chromosome disorders affect “intelligence”

  20. Drug Addiction Compulsively seeking and taking a drug despite knowing its adverse effects Characteristics: - Tolerance = The need to take more of a drug to achieve the same effect - Dependence = The onset of withdrawal symptoms with cessation of drug Evidences is mounting that genes play a role in making some individuals prone to addiction

  21. Drug Addiction Heritability is 0.4-0.6 - Twin and adoption studies support role of genes in drug addiction Drug addiction produces long-lasting changes in the brain Brain changes that contribute to addiction are in the limbic system

  22. The Events of Addiction Figure 8.6

  23. Proteins Involved in Drug Addiction Enzymes involved in biosynthetic pathways of neurotransmitters Neurotransmitter-reuptake transporters Cell-surface receptors Members of signal transduction pathways in postsynaptic neuron

  24. Drugs of Abuse Abused drugs are often derived from plants - Cocaine, opium, and tetrahydrocannabinol (THC), the main ingredient in marijuana - These chemicals bind receptors in human neurons Endorphins and enkephalins are the human equivalents of opiates - Are pain relievers

  25. Candidate Genes for Drug Addiction Nicotine binds a receptor that normally binds acetylcholine, causing dopamine release and pleasure Candidate genes for addiction include those that encode: - The dopamine D(2) receptor A1 alele: overrepresented in alcoholism and others - The nicotine receptor parts Variants of two parts: desire to smoking after first cigarrette - The protein neurexin-1, which ferries nicotinic receptors to neuron’s surface

  26. Mood Disorders Mood disorders represent the extremes of normal behavior The two most prevalent are: - Major depressive disorder = Marked by unexplained lethargy, sadness, and chronic depression - Bipolar affective disorder = Marked by depression interspersed with mania

  27. Major Depressive Disorder Affects 6% of the US population, more women than men A likely cause is a deficiency of the neurotransmitter serotonin,which affects mood, emotion, appetite, and sleep Many antidepressant drugs are selective serotonin reuptake inhibitors (SSRIs)

  28. Major Depressive Disorder:SSRIs: seletive serotonin re-uptake inhibitors Figure 8.7

  29. Bipolar Disorder Also called manic-depression Affects 1% of the population Weeks or months of depression alternate with periods of mania (out of character behaviour) Associated with several chromosome sites Its genetic roots are difficult to isolate

  30. Schizophrenia Loss of ability to organize thoughts and perceptions – withdrawal from reality Worldwide – 1% affected Typically early adult onset Progression - Difficulty paying attention, memory and learning difficulties, psychosis (delusions and hallucinations)

  31. Schizophrenia A heritability of 0.8 and empiric risk values indicate a strong genetic component for schizophrenia

  32. Schizophrenia Dozens of genes may interact with environmental influences to cause this disease One powerful candidate is infection during pregnancy - Prenatal exposure to the influenza or herpes viruses

  33. Autism Autism is a spectrum of disorders - Characterized by loss of language, communication, and social skills, beginning in early childhood - Seizures and mental retardation may occur Autism affects 3-6 children out of every 1,000 - It strikes four times as many boys as girls

  34. Autism More than 30 genes so far have been associated with autism Two genes in particular may finally explain how autism develops - They encode the cell adhesion proteins neurexins and neuroligins - These proteins strengthen synaptic connections in neurons associated with learning and memory

  35. Understanding Autism Autism may arise from failure of synapses to form that enable a child to integrate experiences Figure 8.9

  36. Figure 8.10

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