Fear and the Amygdala Flashcards
1
Q
Where is the amygdala located? What is its function?
A
- Mass of grey matter buried in the anterior medial portions of the temporal lobe, rostral to the hippocampus
- Enables experience and expression of fear. There are many other brain regions implicated in fear and the amygdala is involved in many other emotional processes.
2
Q
Explain Kluver and Bucy’s experiment on monkeys. What effects did it produce?
A
- performed bilateral temporal lobectomy on rhesus monkeys
- Dramatic effects on animals’ aggressive tendencies: animals didn’t display aggression and displayed bizarre behaviours
- visual agnosia, increased oral tendency, decreased emotional reaction, hypersexuality, hypermetamorphosis
- put toy snakes and real snakes in cage but did not show any vocalizations or fearful expressions. Instead, they wanted to play with them.
- Behaviours are replicable in humans with temporal lobe lesions, especially to the amygdala
3
Q
What are the 5 symptoms of Kluver-Bucy Syndrome?
A
- Good visual perception but poor visual recognition
- Increased interest in sex
- Dramatic decrease in fear and aggression (experience of fear)
- Decrease in vocalizations and facial expressions associated with fear (expression of fear)
- Overall flattened emotions
4
Q
What are the 3 nuclei of the amygdala?
A
- Basolateral nuclei: very large in humans; connections with cerebral cortex (orbital and medial PFC)
- Corticomedial nuclei: Connections with olfactory bulb and olfactory cortex
- Central nucleus: Connections with the hypothalamus and brainstem. Also connected to the nucleus of the solitary tract and the parabrachial nucleus (sense what is going on in visceral structures / reaction to physiological response)
5
Q
What are the 3 afferent projections to the amygdala?
A
- Neocortex (all lobes)
- Hippocampal and cingulate gyri
- All sensory systems: All have different patterns to amygdala nuclei and interconnections within the amygdala to integrate different sensory modalities
- Unlike thalamus, most information received by the amygdala is more processed after you are aware what is going on in the environment
6
Q
Explain the role of the cortex in its connections with the amygdala.
A
- Amygdala links cortical regions that process sensory information with hypothalamic and brainstem effector systems
- Cortical input provides highly processed information about visual, somatosensory, visceral, and auditory worlds while the hypothalamus receives relatively raw sensory input
- Amygdala neurons respond to highly complex stimuli, such as faces. However, amygdala also receives bits and pieces of information directly from the thalamus, olfactory bulb, and viscera.
- Amygdala connected to neocortical circuits and hypothalamus in order to integrate emotional significance of sensory information and to influence the expression of complex emotional behaviour.
7
Q
What are the 2 major pathways that connect the amygdala to the hypothalamus?
A
- Ventral amygdalofugal pathway: Projects from basolateral and central nuclei and targets the hypothalamus, basal forebrain, brain stem, and nucleus accumbens. Communicates a required shift in homeostasis.
- Stria terminalis: Band of fibres running along lateral margin of the ventricular surface of the thalamus that is a major output of the amygdala. Runs from the corticomedian nuclei to the ventromedial nucleus of the hypothalamus (which initiates a visceromotor / somatic motor response)
8
Q
What is the commissure that connects the amygdala to the hypothalamus?
A
- Anterior commissure (connects temporal lobes)
9
Q
What are the 2 major tracts from the hypothalamus to the brainstem to control autonomic function?
A
- Medial forebrain bundle: Axons run from the lateral hypothalamus to the ventral segmental area. Stimulation of LH / VTA can elicit predatory aggression while lesions to the VTA can abolish predatory aggression. Stimulation of the hypothalamus will not produce aggressive behaviour is medial forebrain bundle is cut.
- Dorsal longitudinal fasciculus: Axons from medial hypothalamus project to periaqueductal gray matter of the midbrain. Stimulation of PAG elicits affective aggression and lesions to PAG disrupt this behaviour. Requires input from the amygdala.
10
Q
Explain the role of the neocortex’s connections with the amygdala.
A
- Amygdala has connections with several areas in the orbital and medial aspects of the frontal lobes
- Prefrontal cortical fields associate information from every sensory modality on a moment to moment basis
- Amygdala projects to the mediodorsal nucleus of the thalamus, which projects directly to cortical areas
- Amygdala projects to the ventral basal ganglia, which receives projections from the prefrontal cortex involved in emotional processing. Ventral BG is involved in the selection and initiation of behaviours aimed at obtaining rewards and avoiding punishments.
- Amygdala appears to be a nodal point in a network that links cortical and subcortical brain regions involved in emotional processing
11
Q
What is the neural circuitry for the association between stimulus and fear?
A
- All auditory information that reaches the forebrain passes through the medial geniculate complex of the dorsal thalamus
- Response persists if connections between the MGC and auditory cortex is severed
- Response abolished if part of MGC that projects to the amygdala is destroyed
- Projections from the central nucleus to the midbrain reticular formation are critical for freezing behaviours while projections to the hypothalamus are critical for increases in heart rate
- Thus, amygdala is in a position to associate diverse sensory inputs, leading to a new behavioural and autonomic response to stimuli that were previously devoid of emotional content
12
Q
How is the amygdala the site of learning about fearful stimuli?
A
- Amygdala processes both neutral and aversive stimuli
- Establishes connections between neutral sensory stimuli (e.g., tone) and reinforcing stimuli (e.g., foot shock, taste of food)
- Associative learning in the amygdala strengthens connections relaying the information about the neutral stimulus. This requires temporal proximity in the activation of post-synaptic neurons in the amygdala (LTP).
- LTP occurs in the amygdala: NMDA antagonists can abolish condition place aversion
13
Q
What is the neural circuit for learned fear?
A
- The basolateral nucleus is the location of synaptic changes associated with learned fear
- Painful / emotional stimuli lead to changes in synaptic strength that enhance the amygdala’s response to a cue
- Sensory information is sent to the basolateral nucleus and eventually activates the central nucleus
- Central nucleus then projects to
1. Hypothalamus (ANS function)
2. PAG (Behavioural response via somatic motor system)
3. Cerebral cortex (emotional experience)
14
Q
Explain the study that showed that recollection is better for emotional memories.
A
- Showed series of pictures to test subjects: appealing, aversive, or neutral
- Both the appealing and aversive images elicited physiological responses and activity of the amygdala that was greater than that of neutral images
- in second phase of experiment, subject were brought back into PET and asked to use their memories to recall and identify pictures they had seen previously. Subjects recalled emotional pictures better than neutral ones and their ability to recall images was directly proportional to activation of the amygdala in the first phase.
15
Q
What effects have been found when you remove or electrically stimulate the amygdala?
A
- Removal: Reduced fear and aggression; inability to recognize facial expressions (fear, anger, sadness, disgust most common)
- Electrical stimulation: Produces fear and aggression in cats; Increases fear, anxiety, alertness, and vigilance in humans
