Neural Circuits Involved in Fear Conditioning

Neural Circuits Involved in Fear Conditioning

  • Key Structures Involved

    • PeriAqueductal Gray (PAG)

      • Involved in freezing response.

    • Hypothalamus

      • Coordinates autonomic and endocrine responses.

    • Locus Coeruleus

      • Plays a role in arousal and stress response.

    • Central Amygdala

      • Integrates sensory information and mediates emotional responses.

    • Lateral Amygdala

      • Responds to unconditioned aversive stimuli.

    • Thalamus

      • Involved in sensory processing.

  • Unconditioned Stimulus (US)

    • Example: Shock (US)

      • Definition: An unconditioned aversive stimulus that activates the neural circuitry involved in fear responses.

      • Pathway: Activated by shock → lateral amygdala → central amygdala → PAG → hypothalamus → locus coeruleus neuron.

  • Conditioned Stimulus (CS)

    • Example: Tone

      • Initially does not evoke a fear response in the subjects.

      • Raises the question of its activation in the same circuitry as the US.

Exploration of the Conditioned Response

  • Initial Reaction to Tone

    • The first time a rat hears the tone, it questions whether it gets scared.

    • Exploration of the following queries:

      • Does the tone activate the amygdala?

  • Neuronal Activity

    • Different scenarios of the tone and its interaction with lateral and central amygdala neurons.

    • No Amgydala Response:

      • In the first exposure to the tone (CS), there is no response in the amygdala.

      • Key Point: Neuron firing occurs, but without an amygdala activation.

Factors Influencing Amygdala Activation

  • Receptor Availability

    • The reason the tone does not initially activate the amygdala is due to insufficient glutamate receptors.

    • Importance of neurotransmitter glutamate:

      • The tone (CS) does not have enough receptor presence to activate a fear response.

  • Shock Activation

    • In contrast, when a shock (US) is applied:

      • Strong synapse presence with numerous receptors leads to immediate amygdala activation and fear response.

      • Reason: The synapse has lots of glutamate receptors and is inherently powerful due to direct pain association.

  • Fear Response Activation Sequence

    • Tone Followed by Shock:

      • What occurs if the tone (CS) is followed by the shock (US)?

      • Amgydala activation increases leading to conditioned fear learning.

  • Critical Observations

    • When assessing the connection of tone (CS) with future fear responses, the emergence of fear learning is notable.

Conclusion: Fear Learning Dynamics

  • The overall process entails how initial exposures to non-threatening stimuli can transform into conditioned fear due to associations with aversive outcomes (like shock).

  • The interplay of neurotransmitters (particularly glutamate) and receptor availability significantly influences the neural circuitry's response to both conditioned and unconditioned stimuli, culminating in learned fear behavior.