Simple Fear Conditioning: one
tone paired with shock.
Simple fear conditioning still occurs when auditory cortex is lesioned.
Simple fear conditioning does not occur when the part of the thalamus devoted to auditory stimuli is lesioned.
Differential Fear
Conditioning: two tones, only one paired with
shock.
When auditory cortex is lesioned, differential conditioning is not possible.
Note: In rats, an acoustic signal traveling via the thalamus can reach the amygdala in about 12 milliseconds. It takes twice as long via auditory cortex.
Anterograde tracers show four subcortical areas receiving inputs from auditory thalamus.
When the pathway to the amygdala is lesioned, no fear conditioning occurs. Lesioning the other pathways does not affect fear conditioning.
Looking at Specific Regions
Within the Amygdala.
Retrograde tracers show connections from lateral nucleus of the Amygdala to auditory thalamus.
Likewise, anterograde tracers aimed at the same area of the auditory thalamus show connections to lateral nucleus.
Stimulating the central nucleus of the amygdala can trigger freezing and other responses associated with fear.
Lesioning the central nucleus interferes with most fear responses.
Amygdala only structure found so far that is involved in fear conditioning independently of CS and response modalities.
Lesioning the hippocampus eliminates conditioning to context, but does not affect conditioning to a tone.
Extinction is delayed by damage to medial prefrontal cortex.
