Wk3 - Fear Conditioning Flashcards
What brain structure is crucial for fear conditioning?
Amygdala
Define fear conditioning
Creating a fear of an object or situation which was previously neutral
What are some examples of stimuli that can be conditioned?
Tone
Smell / Odour
Light
Context
What are examples of conditioned fear responses?
Autonomic NS activity (HR, BP)
Freezing behaviour
Release of hormones (norepinephrine, epinephrine, stress hormone / ACTH, cortisol)
What differs between organisms in terms of fear conditioning?
Fear response differs between type of organism
Where does fear conditioning occur?
Amygdala
What are the 3 nuclei in the amygdala?
Central nucleus
Lateral nucleus
Basal nucleus
What amygdala nuclei are needed for fear conditioning?
Central nucleus
Lateral nucleus
How was it found out that the central and lateral nuclei of the amygdala are involved in fear conditioning?
Lesions were made in the nuclei of a rat’s amygdala
Looked at the amount of time the rat froze in response to a stimulus, both before and after conditioning.
Control group of unoperated rats. Showed normal fear conditioning (longer freezing time after conditioning)
Found a lack of conditioned response to stimuli when lesions were to the entire amygdala or to the central or lateral nuclei
If CE and LA nuclei were intact, there was a successful conditioned response, even if other nuclei were lesioned
What is the sham condition in the rat experiment and what is it useful for?
Sham condition = operated on but no lesion made.
Shows whether it is the operation that is making the changing in conditioning.
Operating did not have an effect - there was still successful conditioning
What happened to the length of freezing time when either the whole amygdala, the CE nucleus, or the LA nucleus were lesioned?
Little difference in freezing time before and after conditioning. Did not freeze much in response to the conditioned stimulus. Suggests that fear conditioning was unsuccessful.
What nuclei in the amygdala are needed to create a fear?
Central nucleus
Lateral nucleus
What is the role of the lateral nucleus in fear conditioning?
Receives information from the environment and communicates this with the central nucleus
What is the central nucleus’ role in fear conditioning?
Responsible for the fear response (e.g., freezing)
Where does information regarding the neutral stimulus and unconditioned stimulus meet?
Dorsal half of the lateral nucleus of the amygdala
What are the 2 types of cells within the dorsal lateral nucleus of the amygdala?
Trigger cells
Storage cells
How do trigger cells work?
Learn connections rapidly and then go back down to baseline
How do storage cells work?
Learn slowly but never forget. Even if the phobia goes, the pairing of the conditioned stimulus and unconditioned stimulus will be forever stored in the storage cells.
Why can phobias easily resurface under times of stress?
Because the fear-memory of the connection between the conditioned stimulus and unconditioned stimulus will remain in the storage cells of the dorsal lateral nucleus of the amygdala
How have we learnt exactly how fear conditioning in the amygdala works?
Researchers (Le Doux) have taken the amygdala out of the brain and studied it in a Petri dish.
They provided pre-synaptic input which mimics a neutral stimulus tone whilst at the same time providing a large input of injections of current to mimic an electric shock (UCS).
What does the electric shock do to the amygdala in the Petri dish?
Depolarises the cells and creates an action potential
How exactly does the UCS help create a fear response from the NS or CS?
When the cell is depolarised from an electric shock, an action potential occurs. The large influx of Ca2+ allows the weak input from the CS to strengthen.
The signal from the CS jumps on the back of the large action potential of the UCS.
The biochemical changes the strong UCS produces in the cell strengthens the input of the CS, allowing the CS to produce an action potential itself.
How have researchers created a fear response in rats through optogenetics?
Created action potentials in the lateral nucleus cells using optogenetic techniques.
They paired these action potentials with the neutral or conditioned stimuli (e.g., a tone).
Is creating a fear response through optogenetics as robust as the process that would naturally occur and why?
No, it is less robust than the normal type of learning that would occur.
Something was missing, that would normally occur during the pairings and the fear response.
What was the something that was missing?
A neuromodulator
What might a neuromodulator in the brain be needed for?
Needed to boost plasticity
What are examples of neuromodulators?
Brain-stem monoamines (adrenaline and noradrenaline)
What is released during normal shock-tone conditioning?
The shock would normally release brain-stem monoamines, such as adrenaline and noradrenaline
How does fear conditioning affect the brain?
Fear conditioning makes physical, structural changes to the brain (through neuroplasticity)
What role does noradrenaline play in fear conditioning?
Increases learning and increases the conditioned response
What did researcher’s find when they gave the rats a drug to block noradrenaline?
There was decreased learning and they could no longer see the conditioned fear response.
What 3 things are necessary for fear conditioning to occur?
Central nucleus of the amygdala
Lateral nucleus amygdala
Noradrenaline
Describe the mechanism by which fear conditioning works
The neutral stimulus (tone) and the UCS (electric shock) comes into the lateral nuclei of the amygdala
These are paired in the dorsal lateral nucleus
The UCS depolarises the cells in the lateral nucleus
The input from the CS strengthens as it is paired with the UCS
CS can produce an action potential on its own
The information then goes from the lateral nucleus to the central nucleus of the amygdala to produce the fear response.
