Download Chapter 19 study Questions key

Study Questions for Chapter 19
1. What is the purpose of the fear system?
It allows us to escape harmful events and to avoid them in the future.
2. What are some defensive behaviors in rodents and humans?
Freezing, fleeing, and fighting.
3. Describe the predatory imminence gradient.
If a predator is observed at a distance, rats will freeze, but as it gets closer the rat
will flee or fight. Humans react similarly to danger.
4. What brain regions support the fear system?
The prefrontal and perirhinal cortex, thalamus, hippocampus, amygdala, lateral
hypothalamus, and periaqueductal gray.
5. What are the important nuclei in the amygdala that contribute to innate and learned
fears?
The lateral, basal, and central nuclei all contribute to both innate (hard-wired) and
learned fear. The intercalated cells contribute to the extinction of fear.
6. What are the subcortical and cortical pathways?
These are pathways to the amygdala. The subcortical pathway comes directly from
the sensory thalamus, which is thought to provide a somewhat impoverished
representation of the sensory experience. The cortical pathway carries information
from the sensory thalamus to the neocortical regions of the brain including the
perirhinal cortex and hippocampus, which also project to the lateral nucleus and
provide a richer, more detailed representation.
7. Where are clusters of intercalated cells (ITCs) located?
Between the basolateral complex and the central amygdala.
8. What are the two pathways described by Joseph LeDoux that bring the content of an
experience to the lateral nucleus?
The subcortical and the cortical pathways (see question 6).
9. What is extinction? What three observations support the belief that extinction produces
new learning?
If the CS is then presented alone, over time it will lose the ability to evoke the CR.
The three observations are: Spontaneous recovery, the renewal effect, and the
reinstatement effect
10. Define spontaneous recovery, the reinstatement effect, and the renewal effect.
In all 3 cases, recovery of a fear response after extinction occurs even though the CS
and US are never re-paired. Spontaneous recovery can occur when there is a long
retention interval between extinction and the test. Reinstatement occurs if the US is
re-presented without the CS. Renewal can occur when the context where extinction
trials occur is different from the context in which training occurs, and the test
occurs in the training context.
11. What is the relationship between the prefrontal cortex and the amygdala in fear
response modulation?
The PL subregion amplifies the activation of fear neurons in the amygdala, and the
IL region inhibits the fear response by activating intercalated cells. Thus the two
subregions have opposite effects on fear response modulation.
12. Compare and contrast the associative loss hypothesis and the competing memory
theory of extinction.
The associative loss hypothesis assumes that extinction is due to a CS-alone
presentation eliminating the original CS–US association. The competing memory
hypothesis assumes that extinction produces a new association called a CS–noUS
association. The original CS–US association that produced the CR remains intact. If
the CS–noUS association occurs, it inhibits (–) the expression of the conditioned
response.
13. What is the evidence that context specificity of extinction depends on the
hippocampal system?
In experiment done by Maren and colleagues, rats are conditioned to the CS in one
context (context A) but extinguished in a different context (context B). Normal rats
display renewed fear of the CS if they are tested in context A, but display no fear if
tested in context B. In contrast, rats with damage to the hippocampus do not display
renewed fear to the CS when tested in context A.
14. What is the role of NMDA receptors in fear extinction? What is the experimental
evidence?
Because fear extinction is the result of new learning (a CS-noUS association), it is
dependent on NMDA receptor activation. Evidence includes the findings that
NMDA receptor antagonists interfere with extinction, and NMDA agonists facilitate
extinction.
15. What is exposure therapy?
In this therapy, patients with anxiety disorders or post-traumatic stress disorder are
forced to experience the fear-inducing stimulus. This results in extinction of the fear
response.
16. What is the evidence that NMDA receptors might be important in the elimination of
fear when exposure therapy is used?
D-cycloserine, an NMDA receptor agonist that acts on the glycine binding site,
combined with exposure therapy produced a decrease in autonomic arousal and
greater willingness to expose themselves to the fear-inducing stimulus.
17. What are perineuronal nets?
Perineuronal nets are part of the extracellular matrix that surround neurons
(especially inhibitory neurons) and have been discovered to be key developmental
regulators of plasticity. These nets are not present during the period early in
development when extinction training erases the fear memory, but are present later
in development when extinction produces new learning.