Biological bases of behavior (neuroscience, sensation, perception, motivation, emotion)
This domain tests how biology produces behavior: how neurons signal, how drugs alter those signals, how brain systems map onto functions, and how sensory input becomes perception. Expect questions that ask you to predict an outcome rather than recite labels.
Neural signaling
- Resting potential is about -70 mV, maintained by the Na+/K+ pump. An action potential begins with Na+ rushing in (depolarization), then K+ leaving (repolarization); the refractory period enforces one-way travel.
- Transmitters are cleared by reuptake, enzymatic breakdown, or diffusion. Agonists mimic or boost a transmitter; antagonists block it. The same drug can agonize one receptor subtype and antagonize another.
- Key transmitters: acetylcholine (muscle, memory), dopamine (reward, movement, psychosis), serotonin (mood, sleep), norepinephrine (arousal), GABA (main inhibitory), glutamate (main excitatory).
Brain and body systems
- Hindbrain: medulla (vital reflexes), pons, cerebellum (coordination, procedural learning). Limbic: hippocampus (consolidation of declarative memory), amygdala (fear learning), hypothalamus (homeostasis, endocrine control via the HPA axis), thalamus (sensory relay).
- Sympathetic division mobilizes (heart rate up, pupils dilate); parasympathetic restores. Cortisol follows a slower HPA-axis route than adrenaline.
Sensation, perception, motivation
- Absolute threshold = weakest detectable stimulus; difference threshold (JND) = smallest detectable change, proportional to original intensity (Weber's law).
- Signal detection theory separates sensitivity (d-prime) from response bias: a liberal criterion raises both hits and false alarms.
- Perception is top-down (expectations, schemas) as well as bottom-up; Gestalt principles (proximity, similarity, closure) describe grouping.
- Emotion theories: James-Lange (body first), Cannon-Bard (simultaneous), Schachter-Singer two-factor (arousal plus cognitive label), Lazarus (appraisal first).
Worked example
A drug blocks the transporter that clears serotonin from the synapse, and mood lifts only after several weeks. Reasoning: blocking reuptake leaves serotonin in the cleft longer, so this is agonist action at the system level, but the delayed response shows the therapeutic effect is not a simple immediate transmitter increase; downstream receptor adaptation is involved.
Traps
Mixing up James-Lange and Cannon-Bard; calling reuptake inhibition an antagonist effect; confusing absolute threshold with JND; placing declarative memory consolidation in the amygdala rather than the hippocampus.