Amygdala

Question 1

origin of the name amygdala

Answer 1

From greek= almond, because of the almond shape of the structure

Question 2

location of the amygdala

Answer 2

deep in the medial temporal lobe, rostral to the ventral reaches of the hippocampus (on top of the hippocampus)

Question 3

Kühler- Bucy Syndrom

Answer 3

• Damage to the temporal lobe including the amygdala
• also called “psychic blindness”
• symptoms: lack of empathy, hypersexuality, lack of fear

Question 4

the 2 pathways of projection to the amygdala

Answer 4

1. thalamic pathway to the amygdala
2. 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)

Question 5

Cortical input to the amygdala (long path)

Answer 5

• 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

Question 6

Thalamic shortcut to the amygdala (short path)

Answer 6

thalamus–> amygdala

• projection of unprocessed sensory info
• Quick and dirty route

Question 7

why it the thalamic pathway to the amygdala important?

Answer 7

preparedness for biologically meaningful stimuli (dangers)- fear conditioning is induced faster

Question 8

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

Answer 8

B.

Question 9

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

Answer 9

false

Question 10

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

Answer 10

true

Question 11

True/false

cortical activity is important for the supression of amygdala

Answer 11

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.

Question 12

What are the hallmarks of fear? are they appropriate?

Answer 12

• 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.

Question 13

what is the fear centre model?

Answer 13

threat –> sensory system–> fear centre (induces fearful feeling)–> fear response

• assumes that fear feeling induces fear response

Question 14

what is the 2 system mode of fear?

Answer 14

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)

Question 15

the pavlovian fear conditioning test

Answer 15

• 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

Question 16

The role of cortical suppression of amygdala activity in classical fear conditioning

Answer 16

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)

Question 17

the effect of age or cortical degeneration on the amygdala?

Answer 17

reappearance of fears

Question 18

What is memory extinction?

Answer 18

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)

Question 19

How can extinction be measured experimentally (is extinction an active process or forgetting)?

Answer 19

1. 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)

Question 20

How can we test if extinction is permanent?

Answer 20

• 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

Question 21

types of memory

Answer 21

1. declarative memory (medial temporal lobe) -
   a. facts; b. events
2. non-declarative memory-
   a. procedural memory (striatum)
   b. classical conditioning - skeletal (cerebellum); emotional (amygdala)

Question 22

what are the nuclei of the amygdala? how are they organised?

Answer 22

• 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)

Question 23

How is information intregrated in the amygdala?

Answer 23

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

Question 24

Input connectivity in the amygdala

Answer 24

• 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

Question 25

Output connectivity in the amygdala

Answer 25

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)

Question 26

intercalated cells of the amygdala (ITC)

Answer 26

• 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

Question 27

role of BL and CE complexes in fear conditioning

Answer 27

• 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)

Question 28

A possible mechanism for pavlovian fear conditioning

Answer 28

LTP (representing associative learning in the BL complex)

–> blocking synaptic plasticity should impair fear conditioning