Department of Psychiatry, Indiana University School of Medicine
Stark Neuroscience Research Institute
projections necessary for LEARNING to suppress fear to fear+safety cue
Proposed fear suppression circuitry engaged during an explicit safety cue:
single unit recording from the basal amygdala (BA)
We developed a novel behavioral task in order to assess the flexibility and precision of fear and reward-seeking behaviors to discriminative environmental cues.
In this task a Reward Cue is paired with sucrose delivery, a Fear Cue is paired with a mild footshock and a compound Fear Cue+Safety Cue is paired with no footshock.
Both male and female rats show increased reward seeking during the Reward Cue, increased fear behavior during the Fear Cue, but only male rats show suppressed fear behavior during the compound Fear Cue+Safety Cue.
figure adapted from Greiner et al 2019
Behavioral processing of safety cues:
1.females show reduced safety conditioning, reduced fear extinction, and increased reward seeking compared to males (Greiner et al 2019 Behav Brain Res)
2. adolescent preconditioning affects rate of adult safety learning (Müller et al 2018 Sci Rep)
3. prior stress does not impair safety conditioning, but does impair fear extinction and reduces reward seeking (Woon et al 2020 Behav Brain Res)
4. prior stress and prior alcohol history results in generalized freezing to the reward cue which is positively correlated with home cage alcohol consumption (Hackleman et al 2022 Psychopharm)
Amygdala processing of safety cues:
1.neurons in the basal amygdala respond selectively to environmental cues explicitly paired with safety and not to fear or reward cues (Sangha et al, 2013 J Neurosci), a 'safety-specific' microcircuit.
2. a subpopulation of BA neurons show the same neuronal response to safety and reward-associated cues but are not responsive to fear cues (Sangha et al, 2013 J Neurosci), a 'safety+reward' microcircuit. This supports the hypothesis that safety cues engage neuronal circuits encoding reward.
3. safety cue responsive neurons in the basal amygdala switch to responding to the fear cue after fear extinction when fear behavior is reduced (Sangha, 2015 Front Beh Neuro)
4. altering D1 receptor activity in the BLA impairs fear suppression during a safety cue (Ng et al, 2018 Neurobiol Learn Mem)
PFC processing of safety cues:
1. dissociable roles of the prelimbic (PL) and infralimbic (IL) regions of the prefrontal cortex: PL is necessary for discriminatory reward seeking whereas the IL is required to discriminate between the safety and fear cues (Sangha et al, 2014 Neuropsychopharm).
2. neurons in the IL respond selectively to the co-presentation of the fear and safety cues which is positively correlated with safety behavior (Ng & Sangha, 2022 Cerebral Cortex)
In combination with this behavioral task, we use in vivo single unit electrophysiology,
pharmacology and chemogenetics to track biological changes in the brain as the animal is learning about environmental cues signifying safety, fear and reward.
IL neurons projecting specifically to BLA expressing inhibitory DREADD receptors
projection necessary for EXPRESSION of learned fear suppression to fear+safety cue
increased activity leads to LOSS of fear suppression to fear+safety cue