<p>Persistent
and maladaptive fear in the absence of a threat can be disruptive because it
decreases an organism’s opportunity to seek life-sustaining substances. Learned safety signaling can suppress fear
and encourage reward-seeking behavior, thus freeing the organism from fear
induced immobilization. The infralimbic
(IL) region of the prefrontal cortex is important for recalling fear extinction
memories and for suppressing fear via learned safety signals. Neurons in the IL show an excitatory response
to an extinguished fear cue. We thus
hypothesized that neurons in the IL would encode safety by showing an
excitatory response during active fear suppression to a learned safety signal. </p>
<p>To
assess global changes in IL activity, we
monitored IL multi-unit activity to different cues while training animals in a
fear-reward-safety discrimination task (Sangha,
Chadick, & Janak, 2013). During the discrimination
task, male rats learned that the reward cue predicted liquid sucrose, the fear cue
predicted footshock and the joint presentation of both the fear and safety cues
resulted in no footshock. We also
counterbalanced the modality of fear and safety cues (auditory vs visual) with
two separate groups of animals to control for potential sensory modality
effects. Male rats showed high levels of
freezing to the fear cue, and significantly reduced levels of freezing to the
combined fear+safety cue. Male rats also
showed high levels of port activity to the reward cue. There was no significant
difference in the learning rate between the two counterbalanced
conditions. </p>
<p>Our
multi-unit-data showed an increase in IL neuronal firing to the fear+safety cue
across training sessions. This effect was
consistent between the two counterbalanced conditions. We also examined single-unit activity from
all animals that received light as the safety cue (n=8). This allowed us to
examine the population response profile with a subset of the total animals. Although not statistically significant, our
preliminary single-unit data demonstrated a decrease in the percentage of
neurons that showed an inhibitory response to the fear+safety cue, but no
change in the percentage of neurons that showed an excitatory response to the
fear+safety cue. There was also no
change in the magnitude of averaged firing rate in fear+safety excitatory or
inhibitory neurons across training.
Taken together, the decreased inhibition of single-unit activity in the
IL may drive the increased excitation in multi-unit activity in the IL during
behavioral fear suppression to a safety signal.
</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12223823 |
| Date | 30 April 2020 |
| Creators | Ka H Ng (8787026) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/Increased_Neural_Activity_in_the_Prefrontal_Cortex_During_Fear_Suppression_to_a_Safety_Signal/12223823 |
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