biological level (exam 2)

Modern view of nature vs. nurture

The debate no longer exists as either/or; behavior reflects multiple contributors (genes, environment) and their interactions (GxE)

Cell hierarchy

Cells → tissues → organs → systems (e.g., neuron → nervous tissue → brain → nervous system)

DNA

Deoxyribonucleic acid; double-stranded genetic material in the nucleus made of sugar, phosphate, and bases (A, C, G, T); ~3 billion base pairs

Chromosomes

23 pairs of tightly coiled DNA; one of each pair comes from each parent

Gene

Functional segment of DNA that codes for a protein (or RNA); humans have ~20,000

Central dogma

DNA → mRNA → protein

Transcription

DNA is copied into mRNA (in the nucleus)

Translation

Ribosomes read mRNA and build a protein (chain of amino acids)

Uracil

RNA base that replaces thymine from DNA

DNA vs. RNA structure

DNA is double-stranded; RNA is single-stranded

Human DNA similarity

Humans share >99.5% of their DNA sequence

Allele

A different form of a gene (e.g., short vs. long 5-HTTLPR)

Genotype

The combination of alleles inherited from both parents (e.g., AA, AG, GG)

Genetic polymorphism

Common genetic variation found in at least 1% of the population; may affect amount, efficiency, or stability of mRNA and proteins → physiology, cognition, emotion, behavior, personality

Mutation

A much rarer, novel change in DNA sequence (differs from polymorphism by frequency)

SNP

Single Nucleotide Polymorphism; a one-base variation (e.g., A/G SNP → AA, AG, GG genotypes)

Behavior genetics

Field that estimates how much variance in behavior/personality is explained by genes vs. environment using twin and adoption studies; looks at overall genome, not individual genes

MZ twins

Monozygotic (identical) twins; share ~100% of DNA

DZ twins

Dizygotic (fraternal) twins; share ~50% of DNA

Twin correlations (MZ vs. DZ)

MZ correlations are higher on every trait area: general ability .86 vs .62; personality scales .50 vs .28

Twins reared apart

Comparison used to separate genes from environment; MZ twins reared apart still correlate (extraversion .38, neuroticism .38) and show similar mannerisms, attitudes, interests

Shared environment

Environmental influences that make family members more similar (e.g., same home)

Non-shared environment

Environmental influences unique to each person (plus measurement error); explains a large share of Big Five variance

Big Five heritability

Genetic factors explain roughly 30-60% of variance in Big Five traits; evidence of genetic influence for extraversion, neuroticism, agreeableness, conscientiousness

Temperament

Traits visible in early childhood, influenced by genetic and early environmental factors (emotionality, sociability, activity, inhibition)

Emotionality

Tendency to become easily physiologically aroused and experience frequent, intense negative emotions (anger, fear, distress); maternal ratings MZ vs DZ: boys .63 vs 0, girls .73 vs .20

Gene-environment interaction (GxE)

A gene's effect depends on the environment (e.g., 5-HTTLPR × stress → depression)

Candidate gene approach

GxE research investigating specific hypothesized gene (G) and environment (E) factors

Endophenotype

Intermediate measurable trait between a gene and a disorder (gene → endophenotype → disorder)

Gene-environment correlation (rGE)

Genes shape which environments a person experiences (e.g., seeking out stimulating settings)

Epigenetic mechanisms

Environment changes gene expression, NOT the DNA sequence

Serotonin (5-HT)

5-hydroxytryptamine; neurotransmitter associated with social behavior, mood, and depression

Serotonin transporter (5-HTT)

Reuptakes excess serotonin from the synaptic cleft; target of SSRI antidepressants (e.g., Prozac)

5-HTTLPR

5-HTT linked polymorphic region; short (s) allele = less expression, long (l) allele = more expression; genotypes SS, SL, LL; associated with neuroticism

Caspi et al. (2003)

GxE study (Dunedin cohort, birth to 26); s-allele carriers had higher depression probability with more childhood maltreatment/stressful life events; l/l stayed flat; gene alone not associated with depression

Dunedin study

Caspi & Moffitt's longitudinal study following ~1,000 New Zealanders for decades

RDoC approach

Uses intermediate phenotypes of disorders rather than broad diagnostic categories

Common environmental factors studied

Life experiences/stress/trauma; social factors (support, isolation); SES (income, education, occupation); lifestyle (diet, exercise, substances, mindfulness, meaning, purpose)

Glucocorticoids (GCs)

Stress hormones such as cortisol; sustained high levels have negative health effects and can impair the hippocampus

Hippocampus

Brain structure crucial for learning and memory (especially spatial memory)

Stress and the hippocampus

Depression and PTSD are linked to reduced hippocampal volume; longer depression duration → smaller left hippocampus

Maguire et al. (2000)

London taxi drivers had a larger posterior hippocampus than controls (learning city layout → spatial memory)

Level of arousal (LOA)

Brain arousal level; differs between extraverts and introverts

ARAS

Ascending reticular activation system (brainstem); regulates attention, arousal, vigilance, sleep-wake cycles

ARAS in introverts

Small amounts of stimulation overstimulate the ARAS → distress and withdrawal

ARAS in extraverts

Large amounts of stimulation needed to activate the ARAS → seek engaging activities

Optimal level of arousal (OLA)

Hebb; arousal level most appropriate for doing a task effectively; too much or too little undermines performance (Yerkes-Dodson inverted U)

Geen's findings

Introverts preferred lower stimulation and performed worse than extraverts under high stimulation

Behavioral Inhibition System (BIS)

Causes withdrawal from undesirable stimuli; punishment-avoiding; right frontal activity; linked to introversion and anxiety; magnifies reactions to negative events

Behavioral Activation System (BAS)

Directs toward desirable goals/incentives; reward-seeking; left frontal activity; linked to extraversion (NEO-PI-R); magnifies reactions to positive events

BIS/BAS independence

BIS and BAS are functionally independent systems

BIS/BAS Scale

Carver & White (1994); BAS subscales: reward responsiveness, drive, fun seeking

Gable's BIS/BAS findings

BAS sensitivity magnified reactions to positive events and correlated with higher positive affect; BIS sensitivity magnified reactions to negative events

Sensation Seeking Scale (SSS)

4 aspects: thrill and adventure seeking, experience seeking, disinhibition, boredom susceptibility

Sensation seekers

Restless/upset with lack of stimulation; correlated with high optimal level of arousal; low SSS people get stressed when closely confined with another person

High sensation seeker traits

Risk-taking (sex, drugs, driving, sports); prefer complexity, tolerate ambiguity, more creative; liberal/nonconforming; high-stimulation jobs; may view love as a game

Neurotransmitters

Chemicals in nerve cells that transmit impulses across synapses

Monoamine oxidase (MAO)

Enzyme that breaks down serotonin, dopamine, norepinephrine, epinephrine after use; high sensation seekers tend to have LOW MAO → higher NT levels (picture is more complex)

Endocrine glands

Secrete hormones into the bloodstream to maintain homeostasis; slower, widespread, longer-term effects than the nervous system

Purely endocrine organs

Pituitary, pineal, thyroid, parathyroid, adrenal glands (cortex and medulla)

Organs with endocrine cells

Pancreas, thymus, gonads, hypothalamus

Pituitary gland

"Master gland"; releases hormones that signal other glands

Steroid hormones

Lipid-soluble hormones produced from cholesterol (estrogen, progesterone, testosterone, cortisol); ONLY hormones that cross the cell membrane, binding receptors inside the cell → affect transcription

Water-soluble hormones

Amino acid-based hormones; bind receptors on the cell surface

Cortisol

Glucocorticoid released from the adrenal glands; key in the stress response

HPA axis

Hypothalamus (CRH) → pituitary (ACTH) → adrenal gland (cortisol); hypothalamus responds to cortisol level (feedback)

Testosterone and antisocial behavior

High testosterone correlated with assault, going AWOL, drug abuse, multiple sex partners; correlational, complex, interacts with social factors

fMRI

Functional magnetic resonance imaging; traces relations between brain activity (blood flow) and what a person is doing, thinking, feeling

PET

Positron emission tomography; records radioactivity after a nontoxic radioactively-labeled glucose tracer to measure metabolic activity

Amygdala

Almond-shaped forebrain region under the prefrontal cortex; reacts instantly to danger (behavioral, autonomic, endocrine responses); also involved in appetitive responses; fear learning, threat detection

Kagan and the amygdala

Amygdala overactivity linked to temperamental inhibition and shyness

Schwartz et al. (2003)

Infants classified inhibited vs. uninhibited at age 2; at age 22 fMRI, formerly inhibited adults showed greater amygdala activation to novel vs. familiar faces

Reif et al. (2011) NOS1 study

Estonian youth; NOS1 promoter polymorphism × adverse environment (maternal rejection, stressful life events, family relationships) on impulsivity; s/s with more rejection showed highest impulsivity

NOS1

Nitric oxide synthase gene; deletion associated with impulsivity in animals; influences the serotonergic system

BIS-11

Barratt Impulsiveness Scale (outcome measure in NOS1 study; NOT the Behavioral Inhibition System)

AMIS

Adaptive-Maladaptive Impulsivity Scale (outcome in NOS1 study)

Chang et al. OXTR study

OXTR rs53576 A/G polymorphism, oxytocin, dopamine, neuroticism in healthy adults (SPECT, n=82); AA had higher striatal DAT than G-carriers; in G-carriers higher DAT linked to lower oxytocin; DAT correlated with neuroticism only in AA with lower oxytocin

DAT

Dopamine transporter; striatal DAT availability measured by SPECT

OXTR

Oxytocin receptor gene; rs53576 A/G polymorphism (G-carriers vs. AA)

Maudsley Personality Inventory

Neuroticism measure used in the OXTR study

Donaldson & Young study

Oxytocin, vasopressin, and the neurogenetics of sociality; vasopressin receptor levels in reward regions (ventral pallidum) linked to social bonding

Oxytocin and vasopressin

Hypothalamic hormones released from the pituitary; involved in social behavior; have homologs across species

Prairie vs. meadow voles

Prairie voles are monogamous with more vasopressin receptors in VP; meadow voles are polygamous; meadow voles given extra V1a receptors via AAV showed partner preference

avpr1a / AVPR1A microsatellite

Length variation upstream of vasopressin receptor gene; in humans, long alleles → more V1a mRNA and greater amygdala activation to faces; linked to relationship quality and autism

Poole, Jetha & Schmidt study

Retrospective childhood behavioral inhibition (social vs. non-social), adult shyness, salivary cortisol; social inhibition correlated with adult shyness; in females, high cortisol + high social inhibition → highest shyness; no significant results in males

Chein et al. (Steinberg) study

Peers increase adolescent risk taking via reward circuitry; stoplight driving task under fMRI; adolescents made more risky decisions and crashes with peers watching; greater VS and OFC activity with peers in adolescents

LPFC

Lateral prefrontal cortex; activity increased with age (main effect of age); cognitive control

VS and OFC

Ventral striatum and orbitofrontal cortex; reward regions showing age × social context interaction (adolescents most active with peers)