19.4 Learning & Memory

19.4 Learning & Memory

Quick Answer: Learning is a relatively permanent change in behavior from experience; memory is the retention and retrieval of that experience. PA-CAT Behavioral Sciences items test conditioning paradigms, reinforcement schedules, and memory systems.

Classical Conditioning

Ivan Pavlov showed that pairing a neutral stimulus with an unconditioned stimulus (US) that evokes an unconditioned response (UR) converts the neutral into a conditioned stimulus (CS) evoking a conditioned response (CR). In the classic experiment, a bell (CS) paired with food (US) eventually salivated dogs (CR). Acquisition depends on contingency and contiguity. Extinction occurs when the CS is presented without the US; the CR fades but is not erased — spontaneous recovery can reappear. Generalization extends the CR to similar stimuli; discrimination narrows it. Higher-order conditioning pairs a second neutral stimulus with an established CS.

Clinical examples: fear conditioning (amygdala-dependent) underlies phobias; systematic desensitization applies extinction to treat them. Taste aversion (Garcia effect) shows biological preparedness — one-trial learning pairing a flavor with nausea, even with hours-long delay, because evolution prioritizes avoiding poisoned food.

Operant Conditioning

B.F. Skinner showed behavior is shaped by consequences. Reinforcement increases a behavior; punishment decreases it. Each can be positive (adding a stimulus) or negative (removing a stimulus).

A common error is confusing negative reinforcement with punishment. Negative reinforcement removes an aversive to strengthen behavior (e.g., taking aspirin removes a headache, reinforcing aspirin use); it is not punishment.

Schedules of reinforcement control response rate and resistance to extinction:

• Fixed ratio (FR): reward after n responses — high rate, post-reinforcement pause.
• Variable ratio (VR): reward after unpredictable n responses — highest rate, most resistant to extinction (gambling).
• Fixed interval (FI): reward for first response after time t — scalloped pattern.
• Variable interval (VI): reward for first response after unpredictable time — steady, moderate.

Shaping reinforces successive approximations. The Premack principle states a high-probability behavior can reinforce a low-probability one.

Habituation and Sensitization

Habituation is decreased response to a repeated benign stimulus; sensitization is increased response to a repeated or strong stimulus. In the sea slug Aplysia, Eric Kandel showed habituation reduces presynaptic neurotransmitter release at sensory-motor synapses, while sensitization (via serotonin) enhances release — a cellular model of learning. Short-term forms alter existing proteins; long-term forms require gene expression and new protein synthesis (CREB-mediated).

Memory Types

Consolidation stabilizes a memory trace over time; the hippocampus binds elements of an experience, but long-term storage is cortical. Reconsolidation can modify retrieved memories. Forgetting may reflect decay, interference (proactive: old interferes with new; retroactive: new interferes with old), retrieval failure, or motivated forgetting.

Serial Position and Study Strategies

The serial position effect describes superior recall for items at the beginning (primacy effect, transferred to long-term memory) and end (recency effect, still in short-term memory) of a list, with poorer recall of middle items. The spacing effect — distributed study beats massed practice (cramming) — and the testing effect — retrieval practice strengthens memory more than rereading — are the two most robust evidence-based study strategies. State-dependent memory refers to better recall when internal state at retrieval matches encoding (e.g., same mood or caffeine level); context-dependent memory extends this to external environment. The tip-of-the-tongue phenomenon illustrates retrieval failure with partial access — the feeling of knowing without full recall.

Episodic memory (personally experienced events, tied to time and place) and semantic memory (general knowledge, detached from context) are the two declarative subtypes. Autobiographical memory blends episodic and semantic elements. Flashbulb memories are vivid, emotionally charged memories of surprising public events, though their accuracy is often lower than their subjective confidence suggests.

Amnesia: Anterograde (cannot form new memories after insult — patient H.M., bilateral medial temporal resection); retrograde (cannot recall pre-insult events). Korsakoff syndrome (thiamine deficiency, mammillary body damage) features both with confabulation.

Neural Substrates

• Hippocampus — declarative memory consolidation.
• Amygdala — emotional memory, fear conditioning.
• Prefrontal cortex — working memory, retrieval.
• Cerebellum — procedural and motor learning; classical conditioning of motor responses.
• Striatum — habit learning.

Long-term potentiation (LTP) at hippocampal CA3→CA1 synapses (NMDA-receptor dependent) is a leading cellular model of memory; long-term depression (LTD) complements it. Both alter synaptic strength and are thought to underlie the physical trace of memory.