In our new paper we show the role of the infralimbic-to-ventral pallidum pathway in fear extinction learning and compare it to the more studied infralimbic-amygdala pathway.
We first show that IL projections to the ventral pallidum (VP) are denser than IL projections to the basolateral amygdala (BLA), especially from deeper layers.
We then show that neurons in the IL-ventral pallidum pathway become more active and excitable during extinction learning than retrieval.
We also show that inhibiting this pathway during extinction learning prevents the decrease in defensive freezing behavior (but inhibiting the PL-to-ventral pallidum pathway has no effect on extinction learning).
We propose a model of the IL acting as a switchboard operator when it communicates with downstream structures during fear extinction. During extinction learning, IL output to the ventral pallidum is more active, acting to constrain defensive freezing. Then, during extinction retrieval, IL output to the BLA is more active helping downregulate amygdala output (as shown in other work).
Congratulations to everyone whose work contributed to this finding. It is a bittersweet celebration, because we lost Carolina to health complications in August of 2024. We dedicate this work to her fiery spirit.
Thanks to members of the Friedman Lab for their help with the in-vitro recordings.