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Chapter 13 Study Questions Key 1. Describe the memory modulation framework. What is the role of the amygdala, the hippocampus, and the adrenal gland? It suggests that a behavioral experience can have two independent effects. 1) It can activate specific sets of neurons that represent and store the content of the experience; 2) it can activate hormonal and neural systems that can influence the mechanisms that store the memory. The amygdala modulates other regions in the brain; the hippocampus is a key structure for storing information; and the adrenal gland (consisting of the medulla and the cortex) releases hormones that can enhance the strength of the memory. 2. What are memory modulators? Hormonal and other neural systems that are not part of the storage system but can influence the synapses that store the memory. 3. What is the function of epinephrine in the body? Where is it secreted? How is it different from norepinephrine? Epinephrine is secreted from the adrenal medulla when an arousing event occurs. It binds to receptors in the liver, causing the release of glucose into the blood to support the flight-or-flight response, but in the brain the glucose helps to maintain transcription and translation processes that strengthen memory. Norepinephrine is also secreted by the adrenal medulla, but unlike epinephrine, it is also released in the brain as a neurotransmitter. 4. Given that the hormone epinephrine does not cross the blood–brain barrier, how can it influence amygdala function? It does so indirectly by its actions on the vagus nerve. Epinephrine binds to receptors on the vagus nerve, which projects to the brain where it synapses on and activates neurons in the solitary tract nucleus (NTS). These neurons project to the locus coeruleus, which send noradrenergic (norepinephrine) projections to the amygdala. Thus, norepinephrine release in the amygdala is stimulated by peripheral epinephrine acting on the vagus nerve. Epinephrine -> Vagus nerve -> NTS -> LC -> amygdala 5. Describe an experiment that supports the hypothesis that the hormone epinephrine modulates memory storage processes. Injecting rats with epinephrine shortly after training increased inhibitory avoidance when a very low-intensity shock was used. In humans, injections of epinephrine after viewing visual scenes enhanced the memory for the scenes when testing occurred a week later. 6. Which memory tasks can be learned and remembered even with the amygdala removed? Why is that important? Both the place-learning and visible-platform versions of the Morris water-escape task can be learned and remembered even when the amygdala is significantly damaged. This suggests that the amygdala is not an important storage site for the memory trace. 7. What is propranolol, and how is it used in memory modulation experiments? It is a beta-adrenergic receptor antagonist, which blocks the receptors that norepinephrine bind to. If injected into the amygdala after training, it reduces retention of a memory. 8. Several sources of evidence indicate that the basolateral amygdala modulates memory storage. What are they? An injection of lidocaine (a drug that inactivates neurons) into the basolateral amygdala (BLA) following avoidance training impaired the retention of the inhibitory avoidance response. Lidocaine had no effect when it was injected into the central nucleus (CE) of the amygdala. In contrast, injecting clenbuterol (an adrenergic agonist) into the BLA enhanced inhibitory avoidance. 9. What evidence suggests that the amygdala modulates memory strength by regulating the translation of Arc? Lidocaine injected into the amygdala reduces inhibitory avoidance learning and reduces levels of Arc protein in the hippocampus. Conversely, clenbuterol is injected into the amygdala, learning and hippocampal Arc expression are enhanced. 10. What is the evidence for the neuro-hormonal circuit? 1. When epinephrine is administered to anesthetized rats, it activates the vagal nerve, but this outcome is prevented when a beta-adrenergic receptor antagonist is applied. 2. Stimulating the vagus nerve increases glutamate in the NTS. 3. Stimulating the vagus nerve causes burst firing in the locus coeruleus. 11. How is glucose connected to epinephrine and to memory modulation? Epinephrine can bind to receptors in the liver where it can increase the secretion of glucose. Glucose may enhance memory by increasing the phosphorylation of CREB, which acts as a transcription factor. 12. How does glucose release change with age? Does it have effects on memory? Glucose release is dramatically reduced in aged animals, and this is related to increased forgetting associated with aging. 13. What are glucocorticoids? Are they effective memory modulators? Glucocorticoids such as corticosterone are hormones secreted by the adrenal cortex. They can modulate memory, but they do this primarily by enhancing the action of norepinephrine.