NEUR 3207 L8 - Fear & the Amygdala

Emotions and the Amygdala

• Critical for emotions

• Gray matter, in medial temporal lobe.

• Experience and expression of fear, as well as other emotional processing.

Kluver-Bucy Syndrome

• Caused by temporal lobe (amygdala lesions)

• Decreased fear and aggression, flattened emotions.

• Associated with different pathologies; TBI, Stroke, Neuro disease, etc.

Anatomy of the Amygdala

• Basolateral Nuclei

• Corticomedial Nuclei

• Central Nucleus.

• Has many afferent projections.

Basolateral Nuclei

• Subdivided into three main nuclei; Lateral, Basal, and Auxiliary.

• Contains Pyramidal (80/90%) and Non-pyramidal neurons.

• Pyramidal neurons use glutamate and are main projection of BNC.

• Non-pyramidal use GABA and are interneurons.

Corticomedial Nuclei

• Contains PAC which processes olfactory information and sends to Lateral nucleus and hippocampus.

• ACo also for olfaction.

Centromedial Nuclei

• Subdivided into three nuclei; Central, Medial, BNST

• Main output region for amygdala

• Receives and integrates sensory information

• Primarily GABA projections.

Medial Nucleus

• Produces emotional response to chemosignals.

• Receiveds OB inputs and send to Hypothalamus.

• GABA and Glutimate

BNST

• Relay center for Limbic system, Forebrain, Hypothalamus and Brain stem.

• Heterogeneous inputs.

Cortex

• Amygdala linked sensory information from cortex to hypothalamic and brainstem effector regions.

Hypothalamus

• Ventral Amygdalofugal pathway; Basolateral and Central nuclei to hypothalamus, basal forebrain, brain stem and NAc

• Stria Terminalis; Output of amygdala, band of fibers, runs from corticomedial nuclei to ventromedial nucleus of hypothalamus.

• Anterior commissure; connects two temporal lobes.

Midbrain

• Control autonomic function.

• Medial forebrain bundle; runs from LH to VTA, predatory aggression

• Dorsal longitudinal fasciculus; MH to PAG, affective aggression

Neocortex

• Amygdala connects to Orbital and Medial aspects of frontal lobe.

• Amygdala projects to mediodorsal nucleus of hypothalamus which projects to cortical areas.

• Amygdala also projects to BG which receives from cortex.

• Amygdala is nodal point for Cortical and Subcortical regions involved in emotional processing.

Associative Fear

• Conditioned place aversion; mice are in a box with dark and light end, they receive a shock when in dark end, they learn to stay out.

• MGC is necessary (auditory information).

• Central nucleus needed to freeze behaviours.

• Amygdala associates sensory input and leads to behavioural response.

• Amygdala is the site of learning about fearful stimuli.

Learned Fear

• Emotional memories are vivid and long-lasting.

• Basolateral nucleus important for this.

• Painful and emotional stimuli change amygdala’s response to stimuli.

• Emotional activation occurred for both pleasant and unpleasant images.

• Ability to recall images proportional to amygdala activation.

Fear and the Amygdala

• electrical stimulation of amygdala can increase fear, anxiety and aggression.

LTP in Amygdala

• LTP is needed for associative fear responses.

• NMDA antagonists can impair expression of some learned fear responses.

• AMPA antagonists reduce expression of conditional fear

• AMPA agonists enhance fear conditioning.

SM case Study

• Had damaged amygdala

• Very friendly and trusting

• Unable to recognize fear as an emotion

Amygdala and Social Appraisal

• Amygdala used to judge trustworthiness of a person.

• Amygdala activity increases when person deemed untrustworthy.

• Amygdala may make social appraisals before conscious perception.

Anger and aggression

• Male sex hormones drive aggression.

• Predatory aggression; few vocalizations, target head and neck, low ANS activity.

• Affective aggression; Vocalizations, defensive stance, lots of sympathetic activity.

• Amygdalectomie reduced aggression in some patients.

Lateralization of Emotions

• Affective aspects of speech (right hemisphere)

• Left hemisphere (positive emotions) Right hemisphere (negative emotions)

• Individuals are more expressive with left side facial muscles.

• Right hemisphere seems to be more intimately concerned with perception and expression of emotions.

Addiction, Emotions & the Amygdala

• Addiction sometimes viewed as learning in the limbic system

• Limbic loop allows inputs from amygdala and orbital medial PFC to convey emotional reinforcement in NAc

• Three stages; Binge, Withdrawal, Anticipation. Amygdala important in withdrawal and negative affect stage.