15.4 Fear and The Amygdala

Kluver-Bucy Syndrome (cat)

shows amygdala in temporal lobe important for emotion

when animal gets whole temporal lobe removed (1940s) constellation of behavioral changes: after animals are placid not scared or aggressive, less facial expressions, oral fixations, hypersexual, other parts of temporal lobe: vision

anatomy of amygdala, what does it do

two amygdala (amygdalai) name resembles almond
group of nuclei in temporal lobe

responds to threats, fear

also learning with positive associations: linking emotion and memory

Lateral amygdala

gets the perception of stimulus and associates it with smth (ex. smth important, aversive)

Central nucleus (amygdala)

gets association info from lateral amygdala and reacts with fear response

signals to periaqueductal grey (pain area) to prepare defensive behavior

and basial amygdala signals to lateral hypothalamus to autonomic (bodily responses)

bed nucleus of stria terminals → hormones

fear conditioning

neutral stimulis is associated with scary/aversive stimulus (happens together)

(sound comes with electric shock) so just hearing the sound elicits fear response

how does fear conditioning work in the amygdala

the two stimuli (neutral and harmful) get converged in the amygdala

and amygdala sends outputs for behavioral, autonomic, and hormonal responses

what happens when amygdala is lesioned (general)

loss of conditioned fear responses, and fear learning

what is the human evidence for amygdala based fear? (masked images)

masked: person is not consciously aware of scary image (flashing lights) but in response to image, amygdala is active, autonomic response activated (no activation in other areas: prefrontal)

unmasked: also activation in prefrontal cortex etc.

feel fear, react when conscious and unconscious of scary image

damaged amygdala: not scared of external threats, but internal (epinephrine) can get scared

what is dysregulated amygdala indicate

dysregulation of circuits linked with PTSD, fear response is repeatedly activated

what happens when no amygdala (S.M)

rare condition where it gets destroyed
acts similarly to lesioned animals: little fear to threats

trouble recognizing fear in others expressions, but other emotions just fine

who is joseph ledoux

guy who came up with two roads of fear

Two roads of fear

low road (rapid response)

high road (evaluation first)

Low road

stimuli info directly goes from the thalamus to amygdala so its fat and we quickly respond to a threat

High road

info from thalamus goes to cortex and hippocampus first before reaching amygdala

allows for analysis of stimuli before response

what was learned from Synaptic plasticity and fear conditioning

less dendritic spines after fear conditioning

less synaptic spine (reorganized synaptic connection) stronger fear response

Fear extinction

repeated exposure to the stimulus without aversive outcome reduces fear response

(active process, fear will not just become extinct)

what happens to synapses during fear extinction

dendrite spines form in frontal cortex, auditory cortex dendrites are destroyed

(shows diff types of synaptic plasticity are used in fear extinction)

why is it difficult to extinguish a learned fear

its more adaptive we assume that shock/threat will still come

observational fear: what parts involved, and pros

fear of stimuli can come from seeing pain fear of others, rather than direct experience
prefrontal, cingulate cortex
adaptive pros: learning without danger from exposure