Emotion: The Amygdala, Fear, and Anxiety

What are the 3 symptom clusters of PTSD?

1. Re-experiencing trauma through intrusive thoughts, nightmares, flashbacks. 2. Avoidance of social situations and emotional detachment 3. Exaggerated startle, hypervigilance in response to trauma related stimuli

What are the structures involved in fear?

Basolateral amygdala, central nucleus of the amygdala, and the hypothalamus.

A fear inducing stimulus activates the stress hormones:

CRF, ACTH (adrenocorticotropic hormone), and cortisol

What is "learned helplessness" behavioral depression in rat models caused by?

Caused by chronic unpredictable exposure to aversive events. There is an elevation in circulating CRF, which is going to desensitize serotonin receptors in the basolateral amygdala and the medial PFC.

What does fear conditioning do?

Conditioning increases the amplitude of the amygdala's response to the conditioned stimulus and this is in response to the thalamic input

Describe what occurs in Kluver-Bucy Syndrome

Damage to temporal lobe. Decreased fear and aggression, decreased vocalizations and facial expressions and this is most likely due to the destruction of the amygdala.

Describe the projections the hippocampus has that are involved in the context dependent expression of fear?

First, the hippocampus has projections to the basolateral amygdala that can signal to the central nucleus of the amygdala. Second, the hippocampus has projections to the prelimbic cortex in the PFC, which has projections to the basolateral amygdala, which can then signal to the central nucleus of the amygdala.

A fear inducing stimulus activates the release of which neurotransmitters?

Glutamate, norepinephrine, acetylcholine, and dopamine.

What is taking place in fear conditioning?

Glutamatergic mediated enhancement of postsynaptic responding to the thalamic input after conditioning.

Which brain structure is responsible for mediating context dependent extinction?

Hippocampus

Describe the projections the hippocampus has that are involved in the suppression of fear responses following extinction.

Hippocampus to infralimbic cortex located within the PFC, which signals to the intercalated cells, which sends an inhibitory signal to the central nucleus of the amygdala.

In the circuit of Papez, what mediates the physiological manifestations of emotional states?

Hypothalamus

Lesions to the hippocampal formation have no effect on emotional responding to shock. Do lesions at the hippocampal formation impair contextual or cue elicited fear?

Impairs contextual fear.

Where are stimulus-fear associations established?

In the lateral basolateral amygdala

In fear conditioning, we are strengthening connections directly to the output nuclei of the medial portion of the central nucleus AND what is being inhibited?

Inhibiting GABAergic interneurons which would normally act to prevent the medial central nucleus from firing.

The sound of a door being shut causes intense fear in a victim of child abuse. You would expect that this sound produces both rapid onset and high activation of the?

Lateral amygdala

The amygdala receives sensory input from several sources and projects to regions that mediate physiological and behavioral responses. Why is this beneficial?

Learning to produce a certain response under certain conditions is important for us to survive and to stay safe. The amygdala is an area for info to be integrated to induce or produce a changed response.

PTSD is associated with reduced activity of which brain region when exposed to emotional cues?

PFC

These lateral basolateral amygdala neurons are responsive to what?

Painful stimuli, but they also receive auditory and visual inputs.

What would be the consequence of blocking LTP mechanisms in the lateral basolateral amygdala?

Prevents fear conditioning

The basolateral nuclei of the amygdala is important for the _______ experience of fear and important for creating associations between environmental stimuli and actual threatening events.

Psychological

Based on the circuitry of the amygdala, drugs that increase GABAergic function should?

Reduce activity of the medial central nucleus of the amygdala output neurons and decrease the expression of fear

How is the hypothalamus involved in fear?

Releases regulatory hormones that mediates emotional expression of the individual

Lesions of the septum results in?

Septal "Sham" rage - results in extremes of emotion, including explosive violence; disinhibits the hypothalamus

Which portions of the basolateral amygdala receive projections from the CA1 and the subiculum of the hippocampal formation?

The basal and accessory basal

The basolateral complex of the amygdala is composed of?

The basolateral complex consists of the lateral, basal, and the accessory-basal nuclei of the amygdala.

In the circuit of Papez, what mediates the psychological manifestations of emotional states?

The cingulate cortex

The central nucleus of the amygdala is the interface with motor systems and damage to the central nucleus of the amygdala interferes with?

The expression of conditioned fear responses.

What is the role of the hippocampus in context mediated fear conditioning?

The hippocampus is important for understanding what context you should be afraid of a stimulus in. It is important in determining if a certain context is safe or dangerous.

Describe how the hippocampus is involved in the suppressing of fear responses following extinction?

The hippocampus signals to the PFC, more specifically the infralimbic cortex, which then signal to the intercalated cells, which are going to send an inhibitory signal to the central nucleus of the amygdala, which orchestrates the expression of our fear responses.

Which region in the basolateral complex of the amygdala is critical in fear conditioning?

The lateral basolateral amygdala

During fear conditioning, describe the properties of the lateral basolateral amygdala neurons

The lateral basolateral neurons fire sooner and they fire more frequently.

The central nucleus of the amygdala receives inputs from which portions of the basolateral amygdala?

The lateral, basal, and accessory basal amygdala.

What portion of the central nucleus of the amygdala is important for the expression of fear?

The medial portion of the central nucleus

The activity changes in the lateral basolateral amygdala neurons during fear conditioning are in response to input from?

The thalamus, NOT the sensory cortex!

In fear extinction, instead of stimulation of the GABAergic interneurons, what is there?

There is activation and strengthening of connections in the lateral central nucleus that inhibit the GABAergic neuron firing in the medial central nucleus which decreases our response to fear.

How are stress hormones and neurotransmitter release helpful?

These neuromodulators can facilitate learning - they strengthen.

What are benzodiazepines going to do?

They are going to increase the ability of the CNS to inhibit the output neuron in the medial central nucleus. Increasing the ability of the nervous system to inhibit fear expression or fear responding.

What occurs when the basolateral amygdala is removed in terms of a fear response?

They do not show a fear response.

Individuals suffering from PTSD exhibit difficulty using contexts

limit fear responses.