AP Psychology Biological Bases of Behavior — Worked Answer Explanations

Unit 1 · 23 questions explained

Below is a complete answer key for our AP Psychology Biological Bases of Behavior practice questions. For each question you'll find the correct choice, a full written explanation of how to get there, and — for every wrong answer — a short note on exactly why it's tempting and where it goes wrong. Reading these straight through is one of the fastest ways to find the gaps in a unit before exam day.

Prefer to test yourself first? Take the timed Biological Bases of Behavior practice test and come back here to review, or head back to the Biological Bases of Behavior unit overview.

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Question 1 · Easy
Which part of the neuron receives incoming signals from other neurons and carries them toward the cell body?
- A
  Axon
  Why not A: The axon carries signals away from the cell body to other neurons or muscles, not toward it.
- B
  Myelin sheath
  Why not B: The myelin sheath insulates the axon to speed up transmission; it does not receive signals.
- C
  DendritesCorrect
- D
  Terminal buttons
  Why not D: Terminal buttons release neurotransmitters into the synapse; they are the sending end, not the receiving end.
Explanation
Dendrites are the branching extensions of a neuron that receive incoming signals from neighboring neurons and pass them toward the soma (cell body). In contrast, the axon conducts signals away from the soma. Understanding the directional flow — dendrites in, axon out — is foundational to all neural communication.

Key takeaway
Dendrites receive incoming neural signals; axons transmit signals outward.
Question 2 · Easy
A neurotransmitter that generally inhibits neural firing and is linked to anxiety disorders when levels are low is:
- A
  Dopamine
  Why not A: Dopamine is associated with reward, movement, and motivation, not primarily with anxiety inhibition.
- B
  Serotonin
  Why not B: Serotonin influences mood and sleep, and low levels are linked to depression more than to the specific inhibitory role described.
- C
  Acetylcholine
  Why not C: Acetylcholine is involved in muscle activation and memory, not the primary inhibitory neurotransmitter.
- D
  GABACorrect
Explanation
GABA (gamma-aminobutyric acid) is the brain's primary inhibitory neurotransmitter. It reduces neural excitability by binding to receptors and hyperpolarizing neurons. Low GABA activity is associated with heightened anxiety, and many anti-anxiety drugs (benzodiazepines) work by enhancing GABA's inhibitory effects.

Key takeaway
GABA is the main inhibitory neurotransmitter; low GABA activity is linked to anxiety.
Question 3 · Easy
Which brain structure, part of the limbic system, plays a central role in processing fear and emotional memories?
- A
  Hippocampus
  Why not A: The hippocampus is critical for forming new explicit (declarative) memories, not specifically for emotional fear responses.
- B
  AmygdalaCorrect
- C
  Thalamus
  Why not C: The thalamus relays sensory information to the cortex; it is not the primary site of fear processing.
- D
  Cerebellum
  Why not D: The cerebellum coordinates movement and balance; it is not part of the limbic system's emotional circuitry.
Explanation
The amygdala is an almond-shaped limbic structure that evaluates the emotional significance of stimuli and is especially critical for fear conditioning. Damage to the amygdala can impair a person's ability to recognize fearful facial expressions and to form conditioned fear responses, as shown in famous patient cases like S.M.

Key takeaway
The amygdala processes fear and emotional memory within the limbic system.
Question 4 · Easy
Which structure of a neuron is primarily responsible for RECEIVING signals from other neurons?
- A
  Axon
  Why not A: The axon is the long projecting fiber that carries the action potential AWAY from the cell body toward other neurons — it sends signals, not receives.
- B
  DendritesCorrect
- C
  Myelin sheath
  Why not C: The myelin sheath is a fatty insulating layer wrapped around the axon to speed conduction; it doesn't receive signals.
- D
  Terminal buttons
  Why not D: Terminal buttons (axon terminals) are at the END of the axon and release neurotransmitters into the synapse — they send signals to the next neuron.
Explanation
Information flow through a neuron: dendrites RECEIVE signals → soma (cell body) integrates them → axon CARRIES the action potential away → terminal buttons RELEASE neurotransmitters into the synapse → next neuron's dendrites RECEIVE. The myelin sheath wraps the axon and speeds conduction; gaps in myelin (nodes of Ranvier) allow saltatory conduction. Multiple sclerosis is a demyelinating disease that disrupts this conduction.

Key takeaway
Dendrites receive incoming signals; axons send outgoing signals via terminal buttons.
Question 5 · Easy
When a person sees a snake on a hiking trail, their heart rate accelerates, pupils dilate, and breathing quickens. Which division of the nervous system is PRIMARILY responsible for these responses?
- A
  Parasympathetic nervous system
  Why not A: The parasympathetic system does the OPPOSITE: it slows the heart, constricts pupils, and conserves energy ("rest and digest").
- B
  Somatic nervous system
  Why not B: The somatic system controls VOLUNTARY skeletal muscle (e.g., raising your arm). Pupil dilation and heart rate changes are involuntary autonomic responses.
- C
  Sympathetic nervous systemCorrect
- D
  Central nervous system
  Why not D: The CNS (brain + spinal cord) coordinates the response, but the PERIPHERAL output that produces accelerated heart rate, dilated pupils, etc. is specifically the sympathetic branch of the autonomic system.
Explanation
The sympathetic nervous system, part of the autonomic nervous system, mobilizes the body for "fight or flight" — accelerated heart, dilated pupils (more light intake), bronchodilation (more oxygen), suppressed digestion, glucose release. The parasympathetic system is its counterpart for "rest and digest." Both run automatically (autonomic = self-governing). The somatic system, in contrast, handles voluntary movement.

Key takeaway
Sympathetic nervous system mobilizes "fight or flight" responses; parasympathetic enables "rest and digest."
Question 6 · Easy
The endocrine gland known as the 'master gland' because it regulates other endocrine glands is the:
- A
  Thyroid gland
  Why not A: The thyroid regulates metabolism but does not control other endocrine glands.
- B
  Adrenal gland
  Why not B: The adrenal glands release cortisol and adrenaline but are regulated by the pituitary, not the other way around.
- C
  Hypothalamus
  Why not C: The hypothalamus controls the pituitary gland and is sometimes called the 'master of the master gland,' but it is a brain structure, not the master endocrine gland itself.
- D
  Pituitary glandCorrect
Explanation
The pituitary gland, located at the base of the brain and regulated by the hypothalamus, secretes hormones that trigger other endocrine glands (thyroid, adrenal glands, gonads) to produce their own hormones. This hierarchical control earns the pituitary its title as the 'master gland.'

Key takeaway
The pituitary gland is the 'master gland,' directing other endocrine glands via its hormone signals.
Question 7 · Easy
Which neurotransmitter is most directly implicated in Parkinson's disease due to the degeneration of neurons in the substantia nigra that produce it?
- A
  Serotonin
  Why not A: Serotonin depletion is linked to depression and mood disorders, not to the motor tremors of Parkinson's disease.
- B
  Norepinephrine
  Why not B: Norepinephrine is involved in alertness and the fight-or-flight response; its loss is not the primary cause of Parkinson's motor symptoms.
- C
  Acetylcholine
  Why not C: Acetylcholine depletion in the hippocampus and cortex is associated with Alzheimer's disease, not Parkinson's disease.
- D
  DopamineCorrect
Explanation
Parkinson's disease results from the progressive death of dopamine-producing neurons in the substantia nigra, a midbrain structure. Without sufficient dopamine, the basal ganglia cannot properly coordinate movement, resulting in the characteristic tremors, rigidity, and bradykinesia (slowness of movement). Treatment often involves L-DOPA, a dopamine precursor. This contrasts with schizophrenia, which is associated with excess dopamine activity.

Key takeaway
Parkinson's disease: dopamine loss in the substantia nigra disrupts motor coordination.
Question 8 · Easy
The hypothalamus plays a major role in regulating which set of behaviors?
- A
  Voluntary movement and motor planning
  Why not A: Voluntary movement is governed by the motor cortex (frontal lobe) and cerebellum, not the hypothalamus.
- B
  Hunger, thirst, body temperature, and sexual arousal (the "four Fs")Correct
- C
  Long-term episodic memory formation
  Why not C: Long-term episodic memory consolidation is the role of the hippocampus, not the hypothalamus.
- D
  Visual processing
  Why not D: Visual processing happens primarily in the occipital lobe (with input via thalamus relay). The hypothalamus doesn't process vision.
Explanation
The hypothalamus is a small structure beneath the thalamus that regulates homeostatic and motivational behaviors — often summarized as the "four Fs": feeding (hunger), fighting (aggression/temperature), fleeing (fear/arousal), and mating (sex). It controls the pituitary gland (master endocrine gland), regulates circadian rhythms via the suprachiasmatic nucleus, and links the nervous and endocrine systems. Damage produces dramatic changes in eating, drinking, temperature regulation, or sexual behavior.

Key takeaway
The hypothalamus regulates homeostatic drives — hunger, thirst, temperature, sex — and controls the endocrine system via the pituitary.
Question 9 · Easy
REM sleep is characterized by:
- A
  Slow brain waves similar to those during deep sleep, with relaxed muscles
  Why not A: This describes Stage 3 (slow-wave / deep) NREM sleep, characterized by large slow delta waves. REM has FAST, active brain waves.
- B
  Rapid eye movements, active brain waves, and skeletal muscle paralysisCorrect
- C
  The deepest stage of sleep, when sleepwalking and night terrors usually occur
  Why not C: Sleepwalking and night terrors occur during deep NREM sleep (Stage 3), not REM. REM features muscle paralysis precisely to PREVENT acting out dreams.
- D
  A brief transitional phase between waking and falling asleep
  Why not D: This describes Stage 1 NREM sleep, the lightest stage. REM occurs later in the cycle and increases in duration through the night.
Explanation
REM (Rapid Eye Movement) sleep has paradoxical features: brain activity resembling wakefulness (low-amplitude, fast waves), vivid dreaming, rapid eye movements under closed lids, AND atonia (paralysis of skeletal muscle except eye muscles and diaphragm). The paralysis prevents acting out dreams — when it fails (REM behavior disorder), people physically enact their dreams. REM cycles every 90 min through the night, with REM episodes growing longer toward morning.

Key takeaway
REM sleep: active brain waves, vivid dreams, rapid eye movements, and skeletal muscle paralysis (atonia).
Question 10 · Medium
During a sleep study, a participant shows high-amplitude, slow delta waves on an EEG recording. This pattern is most characteristic of which sleep stage?
- A
  REM sleep
  Why not A: REM sleep shows low-amplitude, fast brain waves similar to the awake state, not slow delta waves.
- B
  Stage 1 (N1) NREM sleep
  Why not B: Stage 1 shows theta waves, not the high-amplitude delta waves that characterize the deepest sleep.
- C
  Stage 2 (N2) NREM sleep
  Why not C: Stage 2 features sleep spindles and K-complexes, not predominantly delta waves.
- D
  Stage 3 (N3) NREM sleep — slow-wave sleepCorrect
Explanation
Stage 3 NREM (also called slow-wave sleep or deep sleep) is defined by the dominance of delta waves — large, slow, high-amplitude brain waves. This is the most restorative stage of sleep, during which growth hormone is released and tissue repair occurs. Sleepwalking and night terrors arise from this stage, not from REM.

Key takeaway
Delta waves on an EEG indicate Stage 3 NREM (slow-wave) sleep, the deepest, most restorative sleep stage.
Question 11 · Medium
A researcher lesions the lateral hypothalamus of a rat. Which behavioral change is most likely to result?
- A
  The rat will overeat and become obese.
  Why not A: Overeating and obesity result from lesions to the ventromedial hypothalamus, the 'satiety center,' not the lateral hypothalamus.
- B
  The rat will stop eating and may starve.Correct
- C
  The rat will display heightened aggression.
  Why not C: Heightened aggression is associated with amygdala activity, not lateral hypothalamus lesions.
- D
  The rat will lose the ability to form new memories.
  Why not D: Memory formation depends on the hippocampus, not the hypothalamus.
Explanation
The lateral hypothalamus (LH) functions as the brain's 'hunger center' — it signals that it is time to eat. Destroying the LH results in aphagia (refusal to eat) because the hunger signal is eliminated. Conversely, electrical stimulation of the LH causes eating even in satiated animals. This contrasts with the ventromedial hypothalamus, whose destruction leads to overeating.

Key takeaway
Lateral hypothalamus = hunger center; its destruction causes aphagia (cessation of eating).
Question 12 · Medium
Researchers study identical twins raised apart to investigate the relative contributions of heredity and environment to personality. This research design is best described as a:
- A
  Double-blind experiment
  Why not A: A double-blind experiment requires random assignment to conditions and control of an independent variable, which is not possible with twins.
- B
  Case study
  Why not B: A case study focuses on one individual in depth, not on comparing groups of twins.
- C
  Twin study (natural experiment)Correct
- D
  Cross-sectional study
  Why not D: A cross-sectional study compares different age groups at one point in time, not genetic similarity across environments.
Explanation
Twin studies — especially those comparing identical (monozygotic) twins raised apart — are powerful natural experiments for separating genetic from environmental influences. Because identical twins share 100% of their DNA, similarities despite different upbringings are attributed to heredity, while differences suggest environmental influence. Bouchard's Minnesota Twin Study is the landmark example.

Key takeaway
Twin studies with identical twins raised apart separate genetic from environmental influences on behavior.
Question 13 · Medium
Maria suffered a stroke affecting Broca's area. Which symptom is she most likely to exhibit?
- A
  Inability to understand spoken language
  Why not A: Difficulty understanding spoken language results from damage to Wernicke's area, not Broca's area.
- B
  Loss of visual processing in the left visual field
  Why not B: Visual field deficits result from damage to the occipital lobe or visual cortex, not Broca's area.
- C
  Difficulty producing fluent speechCorrect
- D
  Paralysis of the right hand
  Why not D: Motor paralysis of the right hand would result from damage to the left motor cortex, not specifically Broca's area.
Explanation
Broca's area, located in the left frontal lobe, controls speech production. Damage produces Broca's aphasia — halting, effortful, non-fluent speech with relatively preserved comprehension. Patients often speak in telegraphic phrases ('want milk') and are frustrated by their inability to express themselves. This contrasts with Wernicke's aphasia, where speech is fluent but meaningless.

Key takeaway
Broca's area damage causes non-fluent speech production (Broca's aphasia); Wernicke's area damage causes comprehension problems.
Question 14 · Medium
When a stimulus reaches sufficient strength, a neuron fires an action potential. If the stimulus becomes EVEN STRONGER, what happens to that single neuron's action potential?
- A
  The action potential becomes larger in amplitude.
  Why not A: Action potential AMPLITUDE is fixed (all-or-nothing). Stronger stimuli don't produce bigger action potentials in a single neuron.
- B
  The action potential is unchanged — it is all-or-none — but the neuron may fire MORE FREQUENTLY.Correct
- C
  The action potential travels faster down the axon.
  Why not C: Conduction speed depends on axon properties (diameter, myelination), not stimulus strength. Stronger stimuli don't speed up individual action potentials.
- D
  The action potential reverses direction, traveling backward toward the dendrites.
  Why not D: Action potentials propagate one direction along the axon due to a refractory period that prevents backward travel. Stimulus strength doesn't reverse this.
Explanation
The all-or-none principle: once threshold is reached, a neuron fires an action potential of fixed amplitude — increasing stimulus strength beyond threshold doesn't produce a bigger single action potential. Instead, stronger stimuli encode their intensity through (a) the FREQUENCY of firing (more action potentials per second) and (b) the NUMBER of neurons recruited. This explains how the nervous system can represent a wide range of stimulus intensities with binary firing.

Key takeaway
All-or-none principle: action potentials are fixed-amplitude. Stimulus intensity is encoded through firing frequency, not action potential size.
Question 15 · Medium
Activities like winning a game, eating delicious food, and using addictive drugs all increase activity in brain pathways that release which neurotransmitter — central to the brain's reward system?
- A
  Acetylcholine
  Why not A: Acetylcholine is the neurotransmitter at the neuromuscular junction and in memory/attention systems (depleted in Alzheimer's). Not the primary reward neurotransmitter.
- B
  GABA
  Why not B: GABA is the major inhibitory neurotransmitter, calming neural activity. Reward processing is primarily dopaminergic, not GABAergic.
- C
  DopamineCorrect
- D
  Glutamate
  Why not D: Glutamate is the major excitatory neurotransmitter — broadly involved in learning and signaling — but the SPECIFIC reward/motivation circuit uses dopamine.
Explanation
Dopamine is the primary neurotransmitter in the mesolimbic reward pathway (ventral tegmental area → nucleus accumbens). Activities that the brain treats as rewarding — eating, sex, social validation, exercise, drug use — all release dopamine in this circuit, reinforcing the behavior. Addictive drugs (cocaine, amphetamines, opioids, nicotine) hijack this system, producing far larger dopamine surges than natural rewards. Parkinson's disease involves degeneration of dopamine neurons in a different pathway (substantia nigra → striatum), causing movement difficulties.

Key takeaway
Dopamine is the central reward/motivation neurotransmitter; addictive drugs and natural rewards both act on dopaminergic pathways.
Question 16 · Medium
In split-brain patients (whose corpus callosum has been severed), an image is flashed briefly to the LEFT visual field. The patient is then asked to identify what they saw. What is the typical result?
- A
  The patient can verbally name the object easily.
  Why not A: Verbal naming requires the LEFT hemisphere (where Broca's and Wernicke's areas typically reside). Left visual field projects to the RIGHT hemisphere, which can't transfer the information across the severed corpus callosum to produce speech.
- B
  The patient cannot verbally name the object but can point to it or draw it with the LEFT hand.Correct
- C
  The patient denies seeing anything at all.
  Why not C: The right hemisphere DID process the image. The patient can demonstrate awareness through non-verbal channels (left-hand drawing/pointing). Pure denial would suggest the image wasn't processed.
- D
  The patient can name it with the right hand instead of speaking.
  Why not D: The right HAND is controlled by the left hemisphere, which didn't receive the visual information. The LEFT hand (controlled by the right hemisphere, which did see) is the one that can respond.
Explanation
Sperry and Gazzaniga's split-brain research demonstrated hemispheric specialization. Visual information from the left visual field crosses to the RIGHT hemisphere. In intact brains, the corpus callosum shares this information with the left (language) hemisphere for verbal report. After callosal sectioning (done historically to control severe epilepsy), the right hemisphere has the visual information but cannot transmit it to language areas — so verbal naming fails. The right hemisphere CAN, however, control the left hand to draw or point to what was seen, revealing that the information was processed.

Key takeaway
Split-brain studies reveal hemispheric specialization: language is left-lateralized; each hemisphere processes the opposite visual field and controls the opposite hand.
Question 17 · Medium
Identical (monozygotic) twins reared apart still show striking similarities in personality, intelligence, and certain mental health conditions. These findings provide evidence supporting:
- A
  A heritable (genetic) contribution to these traitsCorrect
- B
  The dominance of nurture over nature
  Why not B: Twins reared APART share genes but NOT environment. Their similarities are therefore evidence FOR genetic contribution, not nurture's dominance.
- C
  That environment plays no role in personality
  Why not C: Heritability estimates are virtually never 100%. Twin similarities support a genetic contribution but don't rule out environmental influence — non-shared environment still matters.
- D
  That epigenetic effects override genetic differences
  Why not D: Epigenetic effects modify gene expression based on environment — they're an ADDITIONAL layer of nature-nurture interaction. The twin-reared-apart similarity is foundational evidence for genetics; epigenetics is a finer-grained mechanism.
Explanation
The classic Minnesota Study of Twins Reared Apart (Bouchard) found that monozygotic twins separated in infancy and raised in different homes still show correlations of ~0.7 for intelligence and notable similarities in personality, interests, and even quirks. Since they share 100% of their genes but ~0% of childhood environment, the similarity must come from genetic factors. Heritability estimates from twin studies typically range from 40-70% for traits like IQ and major personality dimensions — meaningful but not deterministic; environment still accounts for substantial variation.

Key takeaway
Twins reared apart sharing traits demonstrate genetic (heritable) contribution; heritability is meaningful but not deterministic.
Question 18 · Medium
The suprachiasmatic nucleus (SCN) of the hypothalamus plays a KEY role in:
- A
  Regulating the body's circadian rhythm by responding to light cuesCorrect
- B
  Consolidating short-term memories into long-term storage
  Why not B: Memory consolidation is primarily the hippocampus's role, not the SCN's. The SCN regulates timing of biological processes, not memory transfer.
- C
  Balancing fluid intake and thirst
  Why not C: Thirst regulation is a hypothalamic function but is governed by osmoreceptors in other hypothalamic nuclei, not specifically the SCN.
- D
  Regulating breathing rate and reflexes
  Why not D: Breathing is controlled by the medulla (hindbrain), not the SCN.
Explanation
The suprachiasmatic nucleus (SCN) sits in the hypothalamus directly above the optic chiasm, where it receives light-intensity information from the retina (via the retinohypothalamic tract). It uses this input to synchronize the body's master 24-hour clock with the external day-night cycle. The SCN signals the pineal gland to release melatonin in low light, promoting sleep; light suppresses melatonin. Damage to the SCN disrupts circadian rhythms — sleep, hormone release, body temperature, and alertness lose their daily pattern.

Key takeaway
The SCN is the brain's master circadian clock, synchronizing biological rhythms to daylight via retinal input.
Question 19 · Hard
Action potentials follow the all-or-none principle. A researcher increases the intensity of a stimulus applied to a neuron well above threshold. Compared to a threshold-level stimulus, the action potential will:
- A
  Fire with a larger peak voltage to signal stronger stimulation.
  Why not A: The all-or-none principle means the peak voltage of a single action potential is fixed regardless of stimulus intensity.
- B
  Fire with the same peak voltage but a longer duration.
  Why not B: Duration of each action potential is also fixed; intensity is encoded by firing rate, not by individual spike shape.
- C
  Not fire at all, because suprathreshold stimuli are dampened by refractory periods.
  Why not C: Suprathreshold stimuli do trigger action potentials; the refractory period only limits the maximum firing frequency.
- D
  Fire with the same peak voltage and duration, but neurons fire more frequently.Correct
Explanation
The all-or-none principle states that an individual action potential is always the same size and shape once threshold is reached. Stimulus intensity is encoded not by changing the action potential itself, but by increasing the frequency (rate) of firing across the neuron and by recruiting more neurons. This frequency coding is how the nervous system distinguishes a light touch from a painful blow.

Key takeaway
All-or-none principle: action potential magnitude is fixed; stimulus intensity is encoded by firing frequency, not spike size.
Question 20 · Hard
The Weber-Fechner law describes the relationship between physical stimulus intensity and the resulting psychological perception. Which statement best captures this principle?
- A
  The absolute threshold for detecting a stimulus decreases linearly as background noise increases.
  Why not A: This describes signal detection theory's noise floor concept, not Weber's law.
- B
  The just noticeable difference (JND) between two stimuli is a constant proportion of the original stimulus intensity.Correct
- C
  Repeated exposure to a constant stimulus causes the perceived intensity to grow over time.
  Why not C: Repeated exposure causes sensory adaptation — a decrease in perceived intensity — the opposite of growth.
- D
  Perceptual thresholds are identical across all sensory modalities for a given stimulus intensity.
  Why not D: Thresholds differ across modalities; Weber's constant (k) varies by modality (e.g., vision vs. taste).
Explanation
Weber's law states that the just noticeable difference (JND) is a constant fraction (Weber's constant, k) of the original stimulus. For example, you need to add about 2% of weight to notice a difference when lifting objects. This means detecting change in a heavy weight requires adding more grams than detecting change in a light weight — perception scales logarithmically, not linearly. Fechner extended this to a mathematical law: perceived sensation = k × log(stimulus intensity).

Key takeaway
Weber's law: the JND is a constant proportion of the original stimulus; perception scales logarithmically with physical intensity.
Question 21 · Hard
Selective Serotonin Reuptake Inhibitors (SSRIs), commonly prescribed for depression, work by:
- A
  Blocking the reabsorption of serotonin by the presynaptic neuron, increasing its availability in the synapseCorrect
- B
  Causing the presynaptic neuron to release more serotonin per action potential
  Why not B: SSRIs don't increase RELEASE; they block reabsorption (reuptake). The net effect is more serotonin in the synapse, but the mechanism is on the receiving side of the cycle, not the release side.
- C
  Mimicking serotonin at the postsynaptic receptor (acting as serotonin agonists)
  Why not C: Direct receptor agonists (mimicking serotonin) are a different mechanism — used in some drugs like LSD or some migraine medications. SSRIs prolong the action of the body's OWN serotonin.
- D
  Breaking down serotonin enzymes so serotonin lasts longer
  Why not D: Drugs that block the enzyme breaking down monoamines are MAO inhibitors (MAOIs), a different antidepressant class. SSRIs specifically target reuptake, not enzymatic breakdown.
Explanation
After serotonin is released into the synapse and acts on postsynaptic receptors, the presynaptic neuron normally reabsorbs (reuptakes) leftover serotonin via a transporter protein. SSRIs (fluoxetine, sertraline, etc.) block this transporter, leaving serotonin in the synapse longer to keep acting on the postsynaptic receptors. The net effect is enhanced serotonergic signaling. Clinical benefit takes weeks, suggesting downstream adaptations (receptor sensitivity changes, neurogenesis) matter — not just acute serotonin levels.

Key takeaway
SSRIs block serotonin reuptake by the presynaptic neuron, prolonging its synaptic action.
Question 22 · Hard
A split-brain patient has the word 'APPLE' flashed to the left visual field only. When asked to say what was seen, the patient says 'nothing,' but when asked to point with the left hand to the object seen, correctly points to an apple. This finding best demonstrates:
- A
  The role of the hippocampus in consolidating visual memories
  Why not A: The hippocampus is involved in memory consolidation, not the hemisphere specialization demonstrated in split-brain research.
- B
  That the right hemisphere cannot process any visual information
  Why not B: The right hemisphere processes visual information from the left visual field perfectly well; it simply cannot produce spoken language.
- C
  Hemispheric specialization: the left hemisphere controls language; the right hemisphere controls the left handCorrect
- D
  That visual perception requires input from both visual fields simultaneously
  Why not D: Perception can occur with unilateral input; the split-brain results show disconnected processing, not the need for bilateral input.
Explanation
In Sperry and Gazzaniga's split-brain experiments, severing the corpus callosum prevents communication between hemispheres. Information sent to the right hemisphere (left visual field) cannot be verbalized — because language is typically left-hemisphere dominant — so the patient denies seeing anything. However, the right hemisphere can guide the left hand (contralateral control) to identify the object. This reveals that each hemisphere has separate, specialized functions and that consciousness itself can be divided.

Key takeaway
Split-brain research reveals hemispheric specialization: left hemisphere dominates language; right hemisphere controls the left hand via contralateral wiring.
Question 23 · Hard
A patient suffers a stroke and afterward can understand spoken language and read normally, but their own speech is slow, effortful, and limited to short ungrammatical phrases like "want... water... now." This pattern is consistent with damage to which area, and is known as which type of aphasia?
- A
  Wernicke's area; Wernicke's aphasia
  Why not A: Wernicke's aphasia produces FLUENT but meaningless speech and POOR comprehension. This patient's preserved comprehension but halting production points to the opposite pattern.
- B
  Broca's area (left frontal lobe); Broca's (expressive) aphasiaCorrect
- C
  The angular gyrus; alexia
  Why not C: Angular gyrus damage typically affects reading (alexia) or writing (agraphia). This patient reads normally; only speech PRODUCTION is impaired.
- D
  The cerebellum; ataxic dysarthria
  Why not D: Cerebellar damage produces slurred speech (dysarthria) from motor coordination problems, but doesn't typically produce telegraphic, ungrammatical speech with preserved comprehension.
Explanation
Broca's aphasia results from damage to Broca's area in the left frontal lobe (typically the inferior frontal gyrus). Patients show: (1) effortful, slow, telegraphic speech, (2) intact COMPREHENSION (they understand what others say), (3) awareness that they're struggling. Wernicke's aphasia, from posterior left temporal damage, is the opposite: fluent but nonsensical speech ("word salad"), poor comprehension, and lack of awareness of the deficit. Mnemonic: BROCA = Broken speech, Comprehension Adequate; Wernicke = Wordy but Wrong.

Key takeaway
Broca's aphasia: halting/telegraphic production, intact comprehension (left frontal lobe). Wernicke's aphasia: fluent but meaningless speech, poor comprehension (left temporal lobe).