A patient has bilateral amygdala lesions. Which outcome is most consistent with research findings?
AInability to form any new long-term memories
BDifficulty learning fear responses and reduced recognition of threatening stimuli
CLoss of hunger, thirst, and body temperature regulation
DImpaired spatial navigation and route-learning
The amygdala is central to fear conditioning and tagging stimuli with emotional salience. Bilateral amygdala damage (as studied in patient S.M.) impairs fear learning and recognition of fearful expressions while leaving other memory and cognition largely intact. Memory formation requires the hippocampus; hunger and temperature regulation involve the hypothalamus; spatial navigation is hippocampal and entorhinal.
Question 2 True / False
The limbic system exclusively processes negative emotions like fear and anxiety, with little involvement in positive emotional states or reward.
TTrue
FFalse
Answer: False
The amygdala responds to all emotionally salient stimuli — including positive surprises, rewards, and intense positive experiences — not only threats. 'Emotional salience' (significance and arousal) is the better characterization of amygdalar function than 'negative emotion.' The limbic system also interfaces with dopaminergic reward circuitry, which is central to pleasure and motivation.
Question 3 Short Answer
Patient H.M. had his hippocampus surgically removed and afterward could no longer form new declarative memories — yet he could still learn new motor skills like mirror tracing. What does this double dissociation reveal about memory systems in the brain?
Think about your answer, then reveal below.
Model answer: It reveals that the brain has multiple, anatomically distinct memory systems. Declarative (explicit) memory for facts and events depends critically on the hippocampus. Procedural (implicit) memory for skills and habits is stored in the basal ganglia and cerebellum, which were intact in H.M. Damage to one system leaves the other functional.
A double dissociation — where damage to structure A impairs ability X but not Y, while damage to structure B impairs Y but not X — is powerful evidence for distinct systems. H.M. could improve at mirror tracing across sessions but had no memory of having done it before. This cleanly separates 'knowing how' (procedural) from 'knowing that' (declarative) at the neural level.