Psychology & Behavior - Complete Interactive Lesson
Part 1: Sensation & Perception
Psychology & Behavior for the MCAT
Part 1 of 7 — Sensation & Perception
Sensation vs. Perception
- Sensation: Detection of stimuli by sensory receptors (bottom-up)
- Perception: Brain's interpretation of sensory information (top-down)
Sensory Thresholds
| Concept | Definition |
|---|---|
| Absolute threshold | Minimum stimulus detectable 50% of the time |
| Difference threshold (JND) | Minimum change in stimulus detectable 50% of the time |
| Weber's Law | (JND is proportional to stimulus intensity) |
| Signal detection theory | Detection depends on signal strength AND decision criteria (hits, misses, false alarms, correct rejections) |
Sensory Adaptation
- Decreased sensitivity to constant stimuli over time
- Example: You stop noticing the smell of your own house
- Does NOT apply to pain (for survival reasons)
Gestalt Principles of Perception
| Principle | Description |
|---|---|
| Proximity | Near objects grouped together |
| Similarity | Similar objects grouped together |
| Closure | Brain fills in gaps to complete shapes |
| Continuity | Prefer smooth, continuous patterns |
| Figure-ground | Distinguish object from background |
Signal Detection Theory (SDT) — The 2×2 Outcome Matrix
SDT separates sensitivity (how well you discriminate signal from noise, ) from response bias (your willingness to say "yes," criterion β).
| Signal present | Signal absent | |
|---|---|---|
| Said "yes" | Hit | False alarm |
| Said "no" | Miss | Correct rejection |
- A conservative criterion (only respond when very sure) → fewer false alarms but more misses.
- A liberal criterion → more hits but more false alarms.
- Changing payoffs/expectations shifts the criterion WITHOUT changing true sensitivity — this is why SDT data, not raw hit rate, reveals perceptual ability.
Sensory Transduction Pathways (Know the Receptor → Brain Map)
| Modality | Receptor | Primary cortical target |
|---|---|---|
| Vision | Rods/cones → retina | Occipital lobe (V1) |
| Hearing | Hair cells (cochlea, organ of Corti) | Temporal lobe (A1) |
| Touch/pain | Mechanoreceptors / nociceptors | Parietal lobe (somatosensory) |
| Smell | Olfactory receptors | Olfactory bulb → cortex (bypasses thalamus) |
| Taste | Taste buds | Gustatory cortex |
- Place theory (high-frequency pitch coded by WHERE on basilar membrane) vs. frequency/temporal theory (low-frequency pitch coded by rate of firing). High yield for hearing.
- Vision: trichromatic theory (3 cone types) explains the receptor level; opponent-process theory (red–green, blue–yellow, black–white) explains afterimages and downstream processing. Both are correct at different stages.
Bottom-Up vs. Top-Down and Perceptual Constancies
- Bottom-up: data-driven, builds percept from raw features.
- Top-down: concept/expectation-driven (context, priming, schemas).
- Constancies (size, shape, color) keep objects stable despite changing retinal images — a top-down contribution and the source of many size-illusion questions.
Sensation & Perception 🎯
Worked Examples — Sensation & Perception
<details> <summary><b>Example 1: Apply Weber's Law to a new modality</b></summary>Question: A wine taster can just detect a difference when sugar rises from 200 mg/L to 210 mg/L. What is the smallest detectable change at a baseline of 500 mg/L?
Solution:
Key idea: The JND is a constant FRACTION (5%) of the baseline, not a constant absolute amount. At higher intensities you need a larger absolute change to notice it.
</details> <details> <summary><b>Example 2: Interpret a signal-detection data table</b></summary>Question: Over 100 trials with a signal present and 100 with it absent, an observer scores 80 hits and 30 false alarms. Another observer scores 60 hits and 5 false alarms. Who is more sensitive, and who has the more conservative criterion?
Solution:
- Observer A: hit rate 0.80, false-alarm rate 0.30. Observer B: hit rate 0.60, false-alarm rate 0.05.
- Sensitivity () reflects the SEPARATION between hit and false-alarm rates. A: 0.80 − 0.30 = 0.50 gap; B: 0.60 − 0.05 = 0.55 gap → B is slightly more sensitive. ✓
- Criterion: B says "yes" far less often (low false alarms) → B is the more conservative responder; A is more liberal. ✓
MCAT lesson: You cannot judge ability from hit rate alone — a high hit rate paired with a high false-alarm rate just means a liberal criterion.
</details> <details> <summary><b>Example 3: Bottom-up vs. top-down in an experiment</b></summary>Question: Subjects shown a degraded image of an animal identify it faster if they were first told "you'll see a farm animal." Naming this effect and the process involved.
Solution:
- The verbal cue creates an expectation/schema that guides interpretation → top-down processing (specifically, priming). ✓
- The raw degraded pixels alone would be bottom-up; the cue supplies context that fills the gaps.
Connection: This is the same mechanism behind perceptual set and the word-superiority effect — expectation shapes what we perceive, not just what hits the retina.
</details>Key Takeaways — Part 1
- Sensation = detection (bottom-up). Perception = interpretation (top-down).
- Weber's Law: JND is proportional to stimulus intensity ()
- Signal detection theory: both signal AND decision criteria matter
- Gestalt principles: proximity, similarity, closure, continuity, figure-ground
Part 2: Learning & Memory
Psychology & Behavior for the MCAT
Part 2 of 7 — Learning & Memory
Classical Conditioning (Pavlov)
| Term | Definition | Example |
|---|---|---|
| UCS (unconditioned stimulus) | Naturally triggers response | Food |
| UCR (unconditioned response) | Natural response | Salivation |
| CS (conditioned stimulus) | Learned trigger | Bell |
| CR (conditioned response) | Learned response | Salivation to bell |
Key phenomena: Acquisition, extinction, spontaneous recovery, generalization, discrimination
Operant Conditioning (Skinner)
| Type | Effect on Behavior | Example |
|---|---|---|
| Positive reinforcement | Increase (add pleasant) | Treat for good grades |
| Negative reinforcement | Increase (remove unpleasant) | Seatbelt silences alarm |
| Positive punishment | Decrease (add unpleasant) | Speeding ticket |
| Negative punishment | Decrease (remove pleasant) | Phone taken away |
Memory Types
| Type | Duration | Capacity | Example |
|---|---|---|---|
| Sensory | <1 second (iconic) to ~3-4s (echoic) | Large | Flash of image |
| Short-term/Working | ~30 seconds | 72 items | Phone number |
| Long-term | Unlimited duration | Unlimited capacity | Life events |
Reinforcement Schedules (ULTRA HIGH YIELD)
| Schedule | Rule | Response pattern | Real-world example |
|---|---|---|---|
| Fixed ratio (FR) | Reward after set # responses | High rate, brief post-reward pause | Piecework pay (per 10 units) |
| Variable ratio (VR) | Reward after unpredictable # responses | Highest, most resistant to extinction | Slot machines, gambling |
| Fixed interval (FI) | Reward after set time | Scalloped — responding ramps before deadline | Studying right before a weekly quiz |
| Variable interval (VI) | Reward after unpredictable time | Steady, moderate | Checking for a text reply |
Key rule: Ratio schedules (based on # of responses) produce faster responding than interval schedules; variable schedules resist extinction better than fixed. VR is the gold standard for persistence.
Long-Term Memory Subtypes & Encoding
- Encoding effects: spacing effect (distributed > massed practice), serial position (primacy from LTM rehearsal + recency from STM), depth of processing (semantic > acoustic > visual), and state/context-dependent retrieval.
- Memory failures: proactive interference (old disrupts new) vs. retroactive interference (new disrupts old); source monitoring errors; misinformation effect (Loftus).
Biological Basis: Long-Term Potentiation (LTP)
LTP — the cellular model of learning — is strengthening of synaptic transmission via the NMDA receptor, which requires both presynaptic glutamate release AND postsynaptic depolarization to expel its block, allowing influx. The hippocampus is essential for forming new explicit memories (cf. patient H.M., who lost his hippocampi and could form no new declarative memories but could still learn motor skills).
Learning & Memory 🎯
Worked Examples — Learning & Memory
<details> <summary><b>Example 1: Distinguish negative reinforcement from punishment in data</b></summary>Question: A rat presses a lever; this turns off a loud noise. Over sessions, lever-pressing increases in frequency. A second rat presses a lever and receives a shock; pressing decreases. Classify each.
Solution:
- Rat 1: an aversive stimulus (noise) is removed after the behavior, and the behavior increases → negative reinforcement (escape/avoidance learning). ✓
- Rat 2: an aversive stimulus (shock) is added and behavior decreases → positive punishment. ✓
MCAT trap: "Negative" describes removal, not "bad." Whether something is reinforcement or punishment is judged ONLY by whether the behavior goes up (reinforcement) or down (punishment).
</details> <details> <summary><b>Example 2: Interpret a serial-position curve</b></summary>Question: Subjects recall a 20-word list immediately. A U-shaped recall curve appears (best for first and last items). A second group recalls after a 30-second distractor task. What changes, and why?
Solution:
- The immediate curve shows primacy (early items rehearsed into long-term memory) and recency (last items still in short-term/working memory).
- The 30-second distractor task fills working memory and prevents rehearsal → the recency effect disappears while primacy remains. ✓
Why it matters: This double dissociation is classic evidence for SEPARATE short-term and long-term memory stores — a favorite experimental-reasoning question.
</details> <details> <summary><b>Example 3: Apply classical-conditioning terminology to a novel scenario</b></summary>Question: A chemotherapy patient feels nauseated (response) after infusions. Soon, merely entering the clinic waiting room triggers nausea. Identify the UCS, UCR, CS, and CR.
Solution:
- UCS = the chemotherapy drug (naturally causes nausea)
- UCR = nausea caused by the drug
- CS = the waiting room (a previously neutral stimulus paired with the drug)
- CR = nausea triggered by the waiting room alone ✓
Extension: This "conditioned taste/place aversion" can occur after a SINGLE pairing and over long delays — an exception to the usual rule that conditioning needs many closely-timed pairings (biological preparedness).
</details>Key Takeaways — Part 2
- Classical conditioning: association between stimuli (involuntary responses)
- Operant conditioning: consequences shape behavior (voluntary responses)
- Reinforcement increases behavior; punishment decreases behavior
- Memory: sensory → short-term (72 items) → long-term
Part 3: Cognition & Language
Psychology & Behavior for the MCAT
Part 3 of 7 — Motivation, Emotion & Stress
Theories of Motivation
| Theory | Key Idea | AAMC angle |
|---|---|---|
| Instinct | Innate, fixed behavioral patterns | Limited explanatory power for complex behavior |
| Drive reduction | A physiological need creates a drive (tension) that behavior reduces to restore homeostasis | Explains primary drives (hunger, thirst); weak for novelty-seeking |
| Arousal (optimal-arousal) | Organisms seek an optimal level of arousal (Yerkes–Dodson) | Inverted-U; not just need reduction |
| Incentive | External rewards pull behavior (vs. drives that push) | Explains eating dessert when already full |
| Maslow's hierarchy | Physiological → Safety → Love/belonging → Esteem → Self-actualization | Lower needs generally precede higher |
| Self-determination theory (SDT) | Intrinsic motivation from autonomy, competence, relatedness | Distinguishes intrinsic vs. extrinsic |
Yerkes–Dodson Law (Arousal vs. Performance)
- Performance is best at moderate arousal → inverted-U.
- Simple/well-learned tasks: optimal arousal is HIGHER.
- Complex/novel tasks: optimal arousal is LOWER (high arousal disrupts them).
Intrinsic vs. Extrinsic Motivation & the Overjustification Effect
- Intrinsic: doing something for its inherent satisfaction. Extrinsic: for an external reward/avoiding punishment.
- Overjustification effect: giving an extrinsic reward for an already-intrinsically-enjoyed activity can REDUCE intrinsic motivation (the person re-attributes their behavior to the reward).
Theories of Emotion (Know the Sequence)
| Theory | Sequence | One-line distinction |
|---|---|---|
| James–Lange | Stimulus → physiological/bodily response → emotion | "I'm afraid BECAUSE I tremble"; bodily state comes first |
| Cannon–Bard | Stimulus → arousal AND emotion simultaneously | Thalamus relays both at once |
| Schachter–Singer (two-factor) | Stimulus → arousal → cognitive label → emotion | Same arousal + different label = different emotion |
| Lazarus (cognitive-appraisal) | Stimulus → appraisal → arousal + emotion | Appraisal can precede/define the emotion |
- The three components of emotion: physiological, behavioral (expression), and cognitive (subjective experience/appraisal).
Neurobiology of Emotion
- Amygdala: rapid detection of threat/fear; "low road" (thalamus → amygdala) is fast and crude; "high road" (thalamus → cortex → amygdala) is slower and accurate.
- Limbic system (amygdala, hippocampus, hypothalamus) + prefrontal cortex (regulation, especially left/right valence).
- Autonomic signature: sympathetic "fight-or-flight" → ↑HR, ↑BP, pupil dilation, ↓digestion (epinephrine from adrenal medulla).
Stress — Appraisal and Response
- Primary appraisal (is this a threat/challenge/harm?) → secondary appraisal (can I cope?). Stress arises when demands exceed perceived resources.
- Stressors: cataclysmic events, personal life changes, daily hassles.
General Adaptation Syndrome (Selye) & the HPA Axis
- Alarm: acute fight-or-flight (sympathetic + adrenal medulla → epinephrine).
- Resistance: sustained coping via the HPA axis — hypothalamus (CRH) → pituitary (ACTH) → adrenal cortex (cortisol).
- Exhaustion: prolonged cortisol depletes resources → immunosuppression, illness, burnout.
Motivation, Emotion & Stress 🎯
Worked Examples — Motivation, Emotion & Stress
<details> <summary><b>Example 1: Distinguish the emotion theories on one scenario</b></summary>Question: A hiker sees a snake, her heart pounds, and she feels fear. State what each major theory claims about the ORDER of these events.
Solution:
- James–Lange: snake → bodily response (pounding heart) → THEN fear. The emotion is the perception of the bodily state. ✓
- Cannon–Bard: snake → pounding heart AND fear arise simultaneously and independently (thalamic relay). ✓
- Schachter–Singer: snake → arousal → she labels the arousal as "fear" using context (a snake!) → fear. Same arousal labeled differently in another context could be excitement. ✓
- Lazarus: snake → cognitive appraisal ("danger!") → arousal + fear; appraisal can come first.
MCAT note: The discriminating question is always: does the bodily response, the cognition, or both-at-once come first?
</details> <details> <summary><b>Example 2: Apply Yerkes–Dodson to task difficulty</b></summary>Question: Two students take exams under high pressure (high arousal): one faces a simple multiplication drill, the other a novel proof-based problem set. Predict who performs better and why.
Solution:
- Yerkes–Dodson: performance vs. arousal is an inverted-U, and the optimal arousal level DEPENDS on task complexity. ✓
- Simple/well-learned task (multiplication): optimal arousal is HIGH, so high pressure helps or is neutral → that student does fine.
- Complex/novel task (proofs): optimal arousal is LOW, so high pressure pushes past the peak → performance DROPS. ✓
- Conclusion: the multiplication student is least harmed by the high arousal.
Key idea: "Moderate arousal is best" is shorthand — the true peak shifts with task difficulty.
</details> <details> <summary><b>Example 3: Map a stress response onto GAS and physiology</b></summary>Question: A medical resident works grueling shifts for months, then develops frequent infections and exhaustion. Trace the General Adaptation Syndrome stages and the dominant hormone in each.
Solution:
- Alarm (first shifts): acute sympathetic + adrenal-medulla activation → epinephrine/norepinephrine → ↑HR, ↑BP, mobilized glucose. ✓
- Resistance (weeks of sustained demand): the HPA axis dominates → cortisol sustains glucose and suppresses inflammation while the body keeps coping. ✓
- Exhaustion (months): chronic cortisol depletes resources and suppresses immunity → frequent infections, fatigue, burnout. ✓
Connection: Acute stress = epinephrine (fast); chronic stress = cortisol via the HPA axis (slow). Prolonged cortisol explains the immunosuppression and illness.
</details>Key Takeaways — Part 3
- Emotion theories differ on ORDER: James–Lange (body first), Cannon–Bard (simultaneous), Schachter–Singer (arousal + cognitive label), Lazarus (appraisal first).
- Yerkes–Dodson: moderate arousal is best, but the optimum is HIGHER for simple and LOWER for complex tasks.
- Overjustification effect: extrinsic rewards can undermine intrinsic motivation.
- GAS: Alarm (epinephrine, sympathetic) → Resistance (cortisol, HPA axis) → Exhaustion (immunosuppression, illness).
- Amygdala drives rapid fear detection; cortisol is the chronic-stress hormone.
Part 4: Motivation & Emotion
Psychology & Behavior for the MCAT
Part 4 of 7 — Cognition & Consciousness
Cognitive Development (Piaget)
| Stage | Age | Key Feature |
|---|---|---|
| Sensorimotor | 0-2 | Object permanence |
| Preoperational | 2-7 | Egocentrism, lack of conservation |
| Concrete operational | 7-11 | Conservation, logical thinking (concrete) |
| Formal operational | 12+ | Abstract/hypothetical reasoning |
Language Development
| Stage | Age | Example |
|---|---|---|
| Babbling | 6-9 months | "ba-ba-ba" |
| One-word (holophrastic) | 12 months | "mama" |
| Two-word (telegraphic) | 18-24 months | "want cookie" |
| Grammar explosion | 2-5 years | Complex sentences |
Consciousness & Sleep
Sleep Stages:
| Stage | Features | Brain Waves |
|---|---|---|
| NREM 1 | Light sleep, hypnagogic hallucinations | Theta |
| NREM 2 | Sleep spindles, K-complexes | Theta |
| NREM 3 | Deep/slow-wave sleep, hard to wake | Delta |
| REM | Dreams, muscle atonia, rapid eye movement | Beta (like awake!) |
Problem Solving
- Algorithm: Step-by-step guaranteed solution
- Heuristic: Mental shortcut (faster but error-prone)
- Confirmation bias: Seeking evidence that confirms existing beliefs
- Functional fixedness: Can't see new uses for familiar objects
Piaget — Assimilation vs. Accommodation (High Yield)
Piaget argued that children build schemas (mental frameworks) and update them by two complementary processes:
| Process | Definition | Example |
|---|---|---|
| Assimilation | Fitting NEW information into an EXISTING schema | A child who knows "dog" calls a cat a "dog" |
| Accommodation | MODIFYING the schema to fit new information | The child creates a new "cat" schema |
| Equilibration | The drive to balance assimilation and accommodation that propels stage transitions | Resolving the dog/cat conflict |
Trap: Assimilation does NOT change the schema; accommodation does. Vygotsky offers a contrasting sociocultural view — the zone of proximal development (ZPD) and scaffolding emphasize that cognition is built through guided social interaction, not solitary stage-by-stage maturation.
Heuristics & Biases (Tversky & Kahneman)
| Heuristic / Bias | Description | Classic finding |
|---|---|---|
| Availability heuristic | Judge frequency by how easily examples come to mind | People overestimate plane-crash deaths after media coverage |
| Representativeness heuristic | Judge probability by similarity to a prototype | The "Linda problem" — conjunction fallacy (bank teller + feminist judged more likely than bank teller) |
| Anchoring | Over-rely on the first piece of information | Estimates pulled toward an arbitrary starting number |
| Belief perseverance | Clinging to beliefs after they are discredited | Distinct from confirmation bias (which is about evidence search) |
Consciousness-Altering Substances & Theories of Dreaming
- Depressants (alcohol, benzodiazepines, barbiturates): enhance GABA, reduce arousal.
- Stimulants (cocaine, amphetamines, caffeine): increase dopamine/norepinephrine activity.
- Activation-synthesis hypothesis (Hobson & McCarley): dreams are the cortex's attempt to make sense of random pontine (brainstem) signals during REM — contrast with Freud's wish-fulfillment view. The continual-activation / information-processing model holds that REM consolidates memories.
Cognition 🎯
Worked Examples — Cognition & Consciousness
<details> <summary><b>Example 1: Apply a Piagetian stage to a behavior</b></summary>Question: A 9-year-old can correctly reason that if all the water in two identical glasses is equal, pouring one into a taller glass does not change the amount. However, the child struggles to reason about a purely hypothetical scenario ("If you could be invisible, what would you do?") in abstract terms. Which stage is the child in?
Solution:
- Mastery of conservation rules out preoperational; the child has the logical operations of the concrete operational stage (ages 7–11). ✓
- Difficulty with purely abstract/hypothetical reasoning rules out formal operational (12+), which is exactly where such reasoning emerges.
- Conclusion: concrete operational. The child reasons logically about concrete, present objects but not yet about abstractions.
Key idea: Conservation = concrete operational; abstract/hypothetical reasoning = formal operational. The presence of one and absence of the other pins the stage.
</details> <details> <summary><b>Example 2: Identify the sleep stage from EEG data</b></summary>Question: A sleep-lab EEG shows low-amplitude, high-frequency activity resembling the awake state, the EMG shows near-complete loss of skeletal muscle tone, and the participant's eyes are darting under closed lids. When woken, they report a vivid narrative dream. What stage is this?
Solution:
- EEG "like awake" (beta-like, desynchronized) + muscle atonia + rapid eye movements + vivid dreaming = REM sleep ("paradoxical sleep"). ✓
- Contrast: NREM 2 would show sleep spindles and K-complexes; NREM 3 would show high-amplitude delta waves and is the hardest stage to wake from.
MCAT lesson: REM is "paradoxical" because the brain looks awake while the body is paralyzed — the atonia prevents acting out dreams.
</details> <details> <summary><b>Example 3: Classify a reasoning error</b></summary>Question: An investor refuses to sell a failing stock and instead seeks out only news articles predicting the stock will rebound, ignoring analyst downgrades. Classify the dominant cognitive bias and contrast it with a related one.
Solution:
- Selectively SEEKING evidence that supports a pre-existing belief = confirmation bias. ✓
- Contrast with belief perseverance — that would describe clinging to the belief even AFTER the supporting evidence is directly refuted. Here the investor is actively filtering incoming information, so confirmation bias is the better fit.
Connection: Both protect existing beliefs, but confirmation bias is about biased search/interpretation of evidence, whereas belief perseverance is about resistance to disconfirmation.
</details>Key Takeaways — Part 4
- Piaget: sensorimotor → preoperational → concrete → formal operational
- REM sleep: dreams, muscle atonia, beta waves (paradoxical sleep)
- NREM 3 (slow-wave): deep restorative sleep, delta waves
- Heuristics: fast but error-prone. Confirmation bias: seeking confirming evidence.
Part 5: Developmental Psychology
Psychology & Behavior for the MCAT
Part 5 of 7 — Personality & Psychological Disorders
Personality Theories
| Theory | Key Idea |
|---|---|
| Psychoanalytic (Freud) | Id (pleasure), Ego (reality), Superego (morality); unconscious drives |
| Humanistic (Rogers, Maslow) | Self-actualization, unconditional positive regard |
| Trait (Big Five) | Openness, Conscientiousness, Extraversion, Agreeableness, Neuroticism (OCEAN) |
| Social-cognitive (Bandura) | Reciprocal determinism (behavior ↔ cognition ↔ environment) |
| Biological | Temperament, genetics, brain structure |
Freud's Defense Mechanisms
| Defense | Description | Example |
|---|---|---|
| Repression | Pushing threatening thoughts unconscious | Forgetting traumatic event |
| Projection | Attributing own unacceptable feelings to others | Cheater accuses partner of cheating |
| Displacement | Redirecting emotion to safer target | Angry at boss → kicks dog |
| Rationalization | Logical excuse for unacceptable behavior | "I deserved to cheat — the test was unfair" |
| Reaction formation | Acting opposite to true feelings | Being overly kind to someone you hate |
| Sublimation | Channeling unacceptable impulses into acceptable ones | Aggression → contact sports |
Psychological Disorders
| Disorder | Key Features |
|---|---|
| Major Depressive Disorder | Persistent sadness, anhedonia, sleep/appetite changes |
| Bipolar Disorder | Manic and depressive episodes |
| Schizophrenia | Positive symptoms (hallucinations, delusions) + negative (flat affect, social withdrawal) |
| Anxiety Disorders | GAD, panic, phobias, OCD, PTSD |
DSM-5 Categories & Biological Correlates (High Yield)
| Disorder | Distinguishing features | Biological correlate |
|---|---|---|
| Major depressive disorder | weeks of depressed mood OR anhedonia + somatic symptoms | Low serotonin/norepinephrine; targeted by SSRIs |
| Bipolar I | At least one full manic episode (grandiosity, decreased need for sleep, flight of ideas) | Treated with lithium and mood stabilizers |
| Schizophrenia | Positive symptoms (added: hallucinations, delusions) + negative (removed: avolition, flat affect, alogia) for months | Dopamine hypothesis — excess dopamine activity in mesolimbic pathway |
| OCD | Obsessions (intrusive thoughts) + compulsions (ritualized acts that reduce anxiety) | Now classed separately from anxiety disorders in DSM-5 |
| PTSD | Re-experiencing, avoidance, hyperarousal after trauma | Hyperactive amygdala, hippocampal changes |
Positive vs. negative symptoms trap: "Positive" means a behavior is ADDED (hallucination), NOT that it is desirable; "negative" means a normal function is LOST (flat affect). Positive symptoms respond better to typical antipsychotics (D2 blockers).
Personality Theories — Deeper Contrasts
- Freud (psychoanalytic): behavior driven by unconscious conflict among id, ego, superego; psychosexual stages; defense mechanisms reduce anxiety.
- Trait theorists & the Big Five (OCEAN): describe personality on continuous dimensions; the person-situation controversy (Mischel) questioned whether traits predict behavior consistently across situations.
- Social-cognitive (Bandura): reciprocal determinism — behavior, personal/cognitive factors, and environment all influence one another. Locus of control (internal vs. external) and self-efficacy are key constructs.
- Humanistic (Maslow, Rogers): people strive toward self-actualization; Rogers stressed unconditional positive regard and congruence between the real and ideal self.
Personality & Disorders 🎯
Worked Examples — Personality & Disorders
<details> <summary><b>Example 1: Identify the defense mechanism</b></summary>Question: A man who is deeply attracted to a coworker but considers the feeling unacceptable becomes convinced, without evidence, that the coworker is constantly flirting with HIM. Which Freudian defense mechanism is this, and how does it differ from displacement?
Solution:
- The man takes his OWN unacceptable impulse (attraction) and attributes it to another person → projection. ✓
- Displacement would instead redirect the emotion onto a safer target (e.g., snapping at a subordinate), not reassign the impulse's ownership to someone else.
Key idea: Projection = "the feeling is yours, not mine." Displacement = "I'll aim my feeling at a safer target."
</details> <details> <summary><b>Example 2: Distinguish two mood disorders from a vignette</b></summary>Question: A patient reports a one-week period of needing only 3 hours of sleep, racing thoughts, grandiose plans to start five companies, and reckless spending — followed by weeks of depressed mood and anhedonia. What is the most likely DSM-5 diagnosis?
Solution:
- The decreased need for sleep, grandiosity, flight of ideas, and impulsive spending define a manic episode. ✓
- A single full manic episode is sufficient for bipolar I disorder, even with intervening depressive episodes.
- Major depressive disorder is ruled out precisely because mania has occurred — the presence of a manic episode is the deciding criterion.
MCAT lesson: One manic episode = bipolar I. Don't be distracted by the depressive phase; mania is the diagnostic key.
</details> <details> <summary><b>Example 3: Match a personality construct to its theorist</b></summary>Question: A therapist offers a client acceptance and warmth regardless of what the client discloses, aiming to close the gap between the client's real self and ideal self. Name the construct and the theorist.
Solution:
- Acceptance "regardless of what is disclosed" = unconditional positive regard. ✓
- The real-self/ideal-self congruence framework and unconditional positive regard belong to Carl Rogers, a humanistic theorist.
Connection: Contrast with Freud (unconscious conflict) and trait theory (OCEAN dimensions) — humanism is uniquely growth- and self-concept-oriented.
</details>Key Takeaways — Part 5
- Big Five (OCEAN): Openness, Conscientiousness, Extraversion, Agreeableness, Neuroticism
- Freud: Id (pleasure), Ego (reality), Superego (morality) + defense mechanisms
- Schizophrenia: positive symptoms (additions) + negative symptoms (deficits)
- Bandura: reciprocal determinism (person ↔ behavior ↔ environment)
Part 6: Personality & Disorders
Psychology & Behavior for the MCAT
Part 6 of 7 — Neuroscience & Biological Bases of Behavior
Brain Regions
| Region | Functions |
|---|---|
| Frontal lobe | Executive function, planning, personality, motor cortex, Broca's area (speech production) |
| Parietal lobe | Somatosensory cortex, spatial processing |
| Temporal lobe | Auditory processing, Wernicke's area (language comprehension), memory |
| Occipital lobe | Visual processing |
| Cerebellum | Motor coordination, balance |
| Brainstem | Vital functions (breathing, heart rate, sleep) |
Limbic System
| Structure | Function |
|---|---|
| Hippocampus | Memory formation (declarative/explicit) |
| Amygdala | Emotion (especially fear) |
| Hypothalamus | Homeostasis, hormones, 4 F's (fighting, fleeing, feeding, mating) |
| Thalamus | Relay station for ALL senses EXCEPT smell |
Neurotransmitters & Behavior
| NT | Effect | Clinical Connection |
|---|---|---|
| Dopamine | Reward, motivation, movement | Low: Parkinson's. High: Schizophrenia |
| Serotonin | Mood, sleep, appetite | Low: Depression. Targeted by SSRIs |
| Norepinephrine | Arousal, alertness | Fight-or-flight |
| GABA | Inhibition | Low: Anxiety. Targeted by benzodiazepines |
| Acetylcholine | Memory, muscle contraction | Low: Alzheimer's |
Methods for Studying the Brain (Know What Each Measures)
| Technique | What it measures | Strength |
|---|---|---|
| EEG | Electrical activity from scalp electrodes | Excellent temporal resolution; used for sleep stages |
| fMRI | Blood-oxygen-level-dependent (BOLD) signal → indirect neural activity | Good spatial resolution; localizes function |
| PET | Radioactive tracer uptake (e.g., glucose) | Maps metabolic activity, neurotransmitter receptors |
| Lesion / case study | Behavior after damage (e.g., Phineas Gage, H.M.) | Establishes a region's NECESSITY for a function |
Trap: EEG wins on timing (millisecond resolution) but is poor at pinpointing location; fMRI is the reverse. Match the question stem's emphasis to the right tool.
Nervous System Organization & the Autonomic Divisions
- Sympathetic activation: pupils dilate, heart rate up, bronchi dilate, digestion inhibited — driven largely by norepinephrine/epinephrine (adrenal medulla).
- Parasympathetic (vagus-dominated): pupils constrict, heart rate down, digestion stimulated — uses acetylcholine.
Resting Potential & Action Potential (Quantitative Anchor)
The neuron's resting membrane potential is about , maintained by the ATPase (pumps 3 out for every 2 in). Reaching the threshold (~) triggers an all-or-none action potential: influx (depolarization) then efflux (repolarization). The absolute refractory period ensures the impulse travels one direction only.
Neuroscience 🎯
Worked Examples — Neuroscience
<details> <summary><b>Example 1: Localize a deficit to a brain region</b></summary>Question: After a stroke, a patient cannot form any new long-term declarative memories but retains older memories and can still learn new motor skills. Which structure is most likely damaged, and which is spared?
Solution:
- Loss of NEW declarative (explicit) memory formation localizes to the hippocampus (cf. patient H.M.). ✓
- Preserved motor-skill (procedural) learning indicates the cerebellum/basal ganglia are intact — these mediate implicit memory.
Key idea: The hippocampus consolidates new explicit memories; it is not where old memories are permanently stored, which is why remote memories survive.
</details> <details> <summary><b>Example 2: Reason from a neurotransmitter to a disorder/treatment</b></summary>Question: A drug that blocks postsynaptic D2 dopamine receptors reduces a patient's hallucinations and delusions but, over time, produces tremor and rigidity. Explain both effects mechanistically.
Solution:
- Blocking dopamine in the mesolimbic pathway reduces the POSITIVE symptoms of schizophrenia — consistent with the dopamine hypothesis (excess dopamine). ✓
- The same blockade in the nigrostriatal motor pathway lowers dopamine there, mimicking Parkinsonism (tremor, rigidity) — too little dopamine in a motor circuit.
MCAT lesson: The direction of a neurotransmitter's effect depends on the pathway; one drug can fix one circuit while disrupting another.
</details> <details> <summary><b>Example 3: Pick the right imaging method for a study design</b></summary>Question: Investigators want to identify WHICH cortical region activates when subjects view fearful faces versus neutral faces. Which method best fits, and what is its limitation?
Solution:
- The goal is precise spatial localization of activity → fMRI (BOLD signal) is ideal. ✓
- Limitation: fMRI has poor temporal resolution (BOLD lags neural activity by seconds) and measures blood flow indirectly, not neural firing itself.
Connection: If instead they needed millisecond timing of the response, EEG/ERP would be chosen, trading spatial precision for temporal precision.
</details>Key Takeaways — Part 6
- Broca's = speech production (frontal). Wernicke's = comprehension (temporal).
- Hippocampus = memory. Amygdala = fear/emotion. Thalamus = sensory relay (not smell).
- Dopamine: reward + movement. Serotonin: mood. GABA: inhibition.
- Low dopamine → Parkinson's. High dopamine → Schizophrenia.
Part 7: Review & MCAT Practice
Psychology & Behavior for the MCAT
Part 7 of 7 — Development & Identity
Erikson's Psychosocial Stages
| Stage | Age | Crisis |
|---|---|---|
| Trust vs. Mistrust | 0-1 | Infant depends on caregiver reliability |
| Autonomy vs. Shame | 1-3 | Toddler develops independence |
| Initiative vs. Guilt | 3-6 | Child explores and leads |
| Industry vs. Inferiority | 6-12 | Competence in school and social |
| Identity vs. Role Confusion | 12-18 | Adolescent finds self |
| Intimacy vs. Isolation | 18-40 | Young adult forms close relationships |
| Generativity vs. Stagnation | 40-65 | Contributing to society |
| Integrity vs. Despair | 65+ | Reflecting on life's meaning |
Kohlberg's Moral Development
| Level | Reasoning | Example |
|---|---|---|
| Pre-conventional | Self-interest (punishment/reward) | "I'll get in trouble" |
| Conventional | Social norms, law and order | "It's the rule" |
| Post-conventional | Universal ethical principles | "It's the right thing even if illegal" |
Attachment Types (Ainsworth)
| Type | Description |
|---|---|
| Secure | Distressed when parent leaves, happy on return |
| Avoidant | Little distress, ignores parent's return |
| Anxious-ambivalent | Very distressed, ambivalent on return (angry + clingy) |
| Disorganized | No consistent pattern, often from abuse |
The Strange Situation (Ainsworth's Classic Study)
Ainsworth's Strange Situation is a structured observation in which a 12–18-month-old experiences a series of separations from and reunions with the caregiver, plus the presence of a stranger. Reunion behavior, NOT separation distress alone, is the key marker:
- Secure (~60–65% of infants): uses parent as a secure base to explore; upset at departure; readily comforted on reunion.
- Avoidant: explores indifferently; minimal reaction to departure OR reunion.
- Anxious-ambivalent (resistant): little exploration; intense distress; on reunion seeks contact yet resists comfort (clingy + angry).
- Harlow's monkey studies (cloth vs. wire "mothers") earlier established that contact comfort, not feeding, drives attachment — undermining the behaviorist "cupboard love" view.
Comparing the Stage Theorists (Don't Confuse Them)
| Theorist | Domain | Engine of change |
|---|---|---|
| Piaget | Cognitive development | Assimilation/accommodation through 4 stages |
| Erikson | Psychosocial development | Resolving a crisis at each of 8 stages across the lifespan |
| Kohlberg | Moral reasoning | Pre-/conventional/post-conventional levels |
| Vygotsky | Sociocultural cognition | Social interaction; zone of proximal development |
Trap: Erikson stages are psychosocial CRISES (e.g., identity vs. role confusion); Kohlberg's are about the reasoning behind moral choices, NOT the choice itself. A person can reach the same decision at any Kohlberg level — what matters is the justification.
Theories of Identity & Aging
- Marcia's identity statuses (built on Erikson): foreclosure, moratorium, identity achievement, and diffusion — defined by the presence/absence of crisis (exploration) and commitment.
- Activity theory vs. disengagement theory of aging: activity theory holds that maintaining social engagement promotes well-being in older adults; disengagement theory (largely discredited) claimed mutual withdrawal is natural.
Development 🎯
Worked Examples — Development & Identity
<details> <summary><b>Example 1: Match a life situation to an Erikson stage</b></summary>Question: A 50-year-old reports deriving deep satisfaction from mentoring younger colleagues and volunteering, feeling she is "leaving something behind for the next generation." Which psychosocial crisis is she resolving, and in which direction?
Solution:
- Mentoring and contributing to the next generation maps to Generativity vs. Stagnation (middle adulthood, ~40–65). ✓
- She is resolving it toward generativity (productive contribution) rather than stagnation (self-absorption).
Key idea: Generativity is specifically about investing in the NEXT generation and society — distinguish it from Integrity vs. Despair, which is end-of-life reflection on whether one's life had meaning.
</details> <details> <summary><b>Example 2: Classify a study design / observation</b></summary>Question: A researcher subjects 12-month-olds to a sequence of caregiver departures, stranger encounters, and reunions, coding behavior at each reunion. What classic paradigm is this, and what is the primary dependent variable?
Solution:
- The departure-stranger-reunion sequence is Ainsworth's Strange Situation, a structured-observation paradigm. ✓
- The primary measure is reunion behavior (how the infant responds when the caregiver returns), which classifies attachment style — NOT merely how distressed the infant is during separation.
MCAT lesson: Many students wrongly think separation distress is the key variable; it is the reunion response that distinguishes secure from insecure styles.
</details> <details> <summary><b>Example 3: Apply Kohlberg's levels to reasoning</b></summary>Question: A businessman argues he should return a lost wallet "because if word got out that I kept it, my reputation and standing in the community would suffer." Which Kohlberg level is this?
Solution:
- The reasoning centers on social approval, reputation, and meeting others' expectations → the conventional level (specifically the "good boy/good girl" orientation). ✓
- It is NOT pre-conventional (that would cite direct punishment or personal reward) and NOT post-conventional (that would invoke abstract universal principles like honesty as a moral duty).
Connection: Always classify by the JUSTIFICATION, not the action — returning the wallet is "moral," but the reasoning here is conventional, not principled.
</details>Psychology & Behavior — Complete! ✅
The Psych/Soc section tests your understanding of how psychological, social, and biological factors influence behavior and health. Master the major theories (Piaget, Erikson, Kohlberg, Freud), neurotransmitters, brain regions, and learning principles.