Differential effects of predictable vs. unpredictable aversive experience early in development on fear memory and learning in adulthood

We examined the enduring effects of predictable versus unpredictable fear conditioning early in life on memory and relearning in adulthood. At postnatal Day 17 or 25 (P17 or P25), rats either remained naïve, or were fear conditioned using paired (predictable) or unpaired (unpredictable) presentations of white noise and foot shocks. At 2 months of age (adulthood), each group was fear conditioned (or reconditioned) with either paired or unpaired training, and then was tested for fear extinction the next day. Initial findings replicate previous work from our lab and others, demonstrating a difference in adult memory retention based on age of acquisition. Specifically, rats that received paired conditioning at P25, but not P17, show increased freezing to the cue when tested in adulthood. We further show that paired as well as unpaired conditioning at P17 potentiates paired conditioning in adulthood; however, paired, but not unpaired, conditioning at P25 potentiates paired and unpaired conditioning in adulthood. These findings suggest that early predictable versus unpredictable aversive learning at P17 or P25 differentially modulate memory retention and future learning.