Exam 2 biological level

Experience-dependent brain change

Environmental features can change the hardwiring of the brain (neuronal structures), producing stable changes within the person

Epigenetic mechanisms

Environment changes gene expression, NOT the DNA sequence

Reciprocal gene-environment relationship

Genes affect responses to environments; environments change gene expression, brain structure, and physiology, which change behavior

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

Chronic stress → high cortisol → reduced hippocampal volume (impairs learning and new memory formation)

• seen in depression and PTSD

• DNA sequence is NOT changed

Depression duration and the hippocampus

Longer time spent depressed is associated with smaller left hippocampal volume

Maguire et al. (2000)

London taxi drivers had a larger posterior hippocampus than controls; learning the city's layout → spatial memory formation and retrieval

Stress vs. learning effects on the hippocampus

Sustained stress hormones shrink it; repeated active use and learning grow it

Level of arousal (LOA)

Physiological arousal level in the brain; differs between extraverts and introverts

ARAS

Ascending reticular activation system in the brainstem

regulates attention, arousal, vigilance, and sleep-wake cycles

ARAS in introverts vs extraverts

Introverts: even small amounts of stimulation overstimulate the ARAS → distress and withdrawal

Extraverts: large amounts of stimulation are needed to activate the ARAS → seek more engaging activities

Optimal level of arousal (OLA)

arousal level most appropriate for doing a task effectively

too much or too little undermines performance

Yerkes-Dodson law

Inverted-U relation between arousal and performance:

low arousal → boredom/inattention

moderate → optimal

high → anxiety impairs performance

Introvert vs Extravert OLA

Introvert: lower optimal level of arousal → perform better in less stimulating environments

Extravert: higher optimal level of arousal → bored easily, seek stimulation

Geen's findings

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

Behavioral Inhibition System (BIS)

Causes withdrawal from undesirable stimuli

• avoidance and hypervigilance

• punishment-avoiding

• right frontal activity

• linked to introversion and anxiety

• magnifies reactions to negative events

Behavioral Activation System (BAS)

Directs approach toward desirable goals/incentives

• reward-seeking

• left frontal activity

• greater activity in extraverts (NEO-PI-R)

• magnifies reactions to positive events

BIS/BAS independence

BIS and BAS are functionally independent neurological systems

BIS/BAS Scale

measures BIS plus three BAS subscales: reward responsiveness, drive, fun seeking

Carver & White (1994)

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)

tedb

4 aspects

1. thrill and adventure seeking

2. experience seeking

3. disinhibition

4. boredom susceptibility

Sensation seekers

• Restless and upset when stimulation is lacking

• correlated with a high optimal level of arousal

• low scorers get stressed when closely confined with another person

High sensation seeker traits

• Risk-taking (sex, drugs, driving, sports)

• prefer complexity, tolerate ambiguity, more original and creative

• liberal/nonconforming

• prefer high-stimulation jobs

• may view love as a game

Neurotransmitters

Chemicals in nerve cells that transmit impulses from cell to cell across synapses

Monoamine oxidase (MAO)

Enzyme that breaks down serotonin, dopamine, norepinephrine, and epinephrine after use

• high sensation seekers tend to have LOW MAO → higher NT levels

• MAO is NOT the sole cause

No one-to-one mapping

A single physiological pathway rarely maps onto a single personality trait; neural correlates of thoughts, feelings, and behaviors are complex

Endocrine glands

Secrete hormones into the bloodstream to maintain homeostasis

Hormones vs. neurotransmitters

Hormones travel through the blood and act slower, more widespread, and longer-term; neurotransmitters act quickly across synapses (nervous system)

Purely endocrine organs

Organs dedicated solely to hormone secretion: pituitary, pineal, thyroid, parathyroid, adrenal glands (cortex and medulla)

Organs with endocrine cells

Organs that also contain 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); the ONLY hormones that cross the cell membrane; bind receptors inside the cell and affect transcription

Water-soluble hormones

Amino acid-based hormones; cannot cross the cell membrane, so they bind receptors on the cell surface

Cortisol

Glucocorticoid (steroid hormone) released from the adrenal glands; key in the stress response

HPA axis

Hypothalamus releases CRH → pituitary releases ACTH → adrenal gland releases cortisol → short-term stress responses (fight, flight, freeze); hypothalamus responds to cortisol level (feedback)

Testosterone and antisocial behavior

High testosterone correlated with assault, going AWOL, substance abuse, multiple sex partners; correlational only; amplifies dominance-related behavior depending on environment; interacts with social factors such as education

fMRI

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

PET

Positron emission tomography; records radioactivity after a nontoxic radioactively-labeled glucose tracer is injected, measuring metabolic activity

Amygdala

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

Kagan and the amygdala

Amygdala overactivity is linked to temperamental inhibition (caution, fearfulness, withdrawal) and shyness

Schwartz et al. (2003)

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

Blood flow as proxy

In fMRI studies, greater blood flow to a structure is assumed to mean greater activation (a simplification)

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 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

OXTR

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

DAT

Dopamine transporter; striatal DAT availability measured by SPECT

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 (VP) 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 receptors via AAV showed partner preference

avpr1a / AVPR1A microsatellite

Length variation upstream of the vasopressin receptor gene; in humans, long alleles → more 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

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 an age × social context interaction (adolescents most active with peers)