Amygdala Flashcards
origin of the name amygdala
From greek= almond, because of the almond shape of the structure
location of the amygdala
deep in the medial temporal lobe, rostral to the ventral reaches of the hippocampus (on top of the hippocampus)
Kühler- Bucy Syndrom
- Damage to the temporal lobe including the amygdala
- also called “psychic blindness”
- symptoms: lack of empathy, hypersexuality, lack of fear
the 2 pathways of projection to the amygdala
- thalamic pathway to the amygdala
- cortical pathway to the amygdala
sensory input goes to the thalamus–> thalamus projects to the sensory cortex and to the amygdala (pathway 1) –> sensory cortex projects also to the amygdala (pathway 2)
Cortical input to the amygdala (long path)
- sensory input from thalamus–>sensory cortex–> hippocampus + amygdala–> hippocampus also project to amygdala
- projection of processed sensory info
- precise, exact and experience dependent
- rather slow
Thalamic shortcut to the amygdala (short path)
thalamus–> amygdala
- projection of unprocessed sensory info
- Quick and dirty route
why it the thalamic pathway to the amygdala important?
preparedness for biologically meaningful stimuli (dangers)- fear conditioning is induced faster
which statement/s is/are correct
a. the thalamic input always controls the cortical input
b. the thalamic input is faster than the cortical one, but less precise since the sensory info is less processed
c. cortical input is faster than the thalamic one, since the cortical neurons are evolutionary younger and have faster propagation speed in APs
d. Thalamic and cortical inputs are equally fast, but the thalamic one is stronger
e. Thalamic and cortical inputs are equally fast, but the cortical one is stronger
B.
True/false:
Fight or flight responses are controlled by the basolateral complex of the amygdala, whereas passive responses like freezing are controlled by the central amygdala
false
True/false:
The basolateral complex receives most of the cortical and thalamic input. it is responsible for the acquisition of memory. Fear related behaviour is elicited by the central amygdala
true
True/false
cortical activity is important for the supression of amygdala
true, the cortical activity controls unnecessary amygdala activity. This means that fear memories never go away, but rather they are suppressed by the cortical pathways.
What are the hallmarks of fear? are they appropriate?
- freezing (always 1st reaction in all animals)
- Heartbeat + blood pressure increase
- sweating
- Defecation (important and easily measured in animal experiments)
- vocalisation
- hormonal effects- stress hormones (only in prolonged fear)
–> these are all physical measurements, and thus may not be appropriate readouts, since sometimes cognitive fear may still be present, and fear response not so much.
what is the fear centre model?
threat –> sensory system–> fear centre (induces fearful feeling)–> fear response
- assumes that fear feeling induces fear response
what is the 2 system mode of fear?
threat–> sensory input –> 2 pathways:
a. cognitive circuit –> induces fear feeling
b. defensive/survival input –> induces fear/defensive response (+ sending info to the cognitive circuit)
the pavlovian fear conditioning test
- A naive animal is presented with a harmful, unconditioned stimulus (US) that is paired with a harmless, conditioned cue (CS) –>naive animal develops a fear response
- After pairing US and CS, the presentation of only the tone (CS) should elicit a fear response
naive animal –> (conditioning: tone + shock)–> animal freezes–> (presenting only tone)–> animal freezes
The role of cortical suppression of amygdala activity in classical fear conditioning
After multiple repetitions of CS without US the animal learns that CS isn’t dangerous –> fear response decrease due to learning induced by cortical pathway)
the effect of age or cortical degeneration on the amygdala?
reappearance of fears
What is memory extinction?
After repetitive exposure to the conditioned stimulus (CS) without the unconditioned stimulus there is decrease in fear response (less time spent freezing).
- IT IS NOT THE SAME AS FORGETTING, but an active process of relearning.
- requires the presence of CS alone
- cue specific
- not permanent (spontaneous recovery, renewal/context dependent, reinstatement)
How can extinction be measured experimentally (is extinction an active process or forgetting)?
- 2 groups are tested for fear conditioning–> later, 1 group is left undisturbed, and the other group is presented only with CS repetitively–> if fear response decreases in the latter group but not in the first group –> extinction is an active process (requires the presence of CS alone)
How can we test if extinction is permanent?
- spontaneous recovery- measure the response at different time points (0, 2h, 24h..)
- renewal (presence of different contexts)
- reinstatement- unsigned US presentation should reinduce fear response
types of memory
- declarative memory (medial temporal lobe) -
a. facts; b. events - non-declarative memory-
a. procedural memory (striatum)
b. classical conditioning - skeletal (cerebellum); emotional (amygdala)
what are the nuclei of the amygdala? how are they organised?
- lateral amygdala (LA)
- basal amygdala (B)
- central amygdala (CE, lateral/medial)
–> basolateral complex is a cortical region, central complex is a ventral extension of the striatum)
How is information intregrated in the amygdala?
sensory stimuli go to the LA–> projection to other parts of the amygdala (basal, central)–> info from B also projects to CE–> emotional response
LA to CE- sparse connectivity
LA to B- processing of learned fear
CE- output- mainly inhibitory projections
Input connectivity in the amygdala
- Sensory input from thalamus & cortex –>LA
- Hippocampus & entorhinal cortex –> LA + B
- Polymodal, association cortex–> B
- Prefrontal cortex–> B, ITC, CE
- Viscero sensory cortex & sensory brainstem–> CE
- Olfactory bulb–> CeM
Output connectivity in the amygdala
B–> prefrontal cortex (regulation), polymodal, association cortex (cognition), ventral striatum (instant actions)
CE–> modualtory systems (arousal), periaqueductal gray (freezing), hypothalamus (sympathetic NS, hormones), dorsal Mot N. Vagus (parasympathetic NS)
intercalated cells of the amygdala (ITC)
- a group of GABAergic neurons situated between the basolateral and central nuclei of the amygdala that are important for inhibitory control over the amygdala
- controls the amygdala via a local feedforward inhibition –> input gating to the amygdala
- -> outcome of feedforward inhib.: inhibition is delayed- excitatory response occurs after input comes to LA –> inhibition by ITC
- ITC surpasses the output without removing LTP
role of BL and CE complexes in fear conditioning
- the basolateral complex is important for acquisition of memory (main input of the amygdala)
- the central complex is responsible for generation of fear behaviour (main output areal)
A possible mechanism for pavlovian fear conditioning
LTP (representing associative learning in the BL complex)
–> blocking synaptic plasticity should impair fear conditioning
