Biological Bases of Behavior
Build the systems map
Questions here reward a hierarchy: neuron → neurotransmitter → circuit → lobe → behavior. Know that the resting potential is roughly −70 mV, that the action potential is all-or-none, and that postsynaptic potentials (EPSPs/IPSPs) are graded and summate. Match transmitters to functions: dopamine (reward, motor control, psychosis, Parkinson's), serotonin (mood, sleep, OCD), norepinephrine (arousal, anxiety), GABA (inhibitory; benzodiazepines increase its effect), glutamate (excitation, learning), acetylcholine (muscle contraction, memory; depleted in Alzheimer's).
Localization
Broca's area (left frontal) produces nonfluent, effortful speech with relatively preserved comprehension and preserved awareness of the deficit. Wernicke's (left posterior temporal) produces fluent but empty speech with poor comprehension, poor repetition, and often anosognosia. Conduction aphasia (arcuate fasciculus damage) spares fluency and comprehension but wrecks repetition. Split-brain patients can retrieve an object placed in the left hand (right hemisphere) but cannot name it, because naming is lateralized to the left hemisphere in most people.
Traps
- CT and MRI are both structural; CT is fast and shows bone and acute hemorrhage, MRI has better soft-tissue resolution. fMRI (BOLD signal) and PET (metabolism) are functional-do not label them structural.
- Sympathetic = fight-or-flight (pupil dilation, increased heart rate, dry mouth); parasympathetic = restoration and digestion.
- Antipsychotics: extrapyramidal symptoms early, tardive dyskinesia late.
Rule of thumb
When a stem describes the quality of speech and comprehension, classify the aphasia before anything else: fluent + unaware = Wernicke; halting + aware = Broca.