Research reportA sensory-enhanced context allows renewal of an extinguished fear response in the infant rat

- ABA-renewal is not observed in infant rats when using standard contexts (without explicit odors).
- The ABA-renewal procedure was effective in reinstating the extinguished CR when contexts (A and B) included an explicit odor.
- This is the first evidence of renewal of an extinguished fear conditioning response in the infant rat.

Studies of extinction in preweanling rats have failed to find ABA-renewal in a fear conditioning paradigm. This result supports the hypothesis postulating ontogenetic qualitative differences in experimental extinction. A similar result in adult rats led to the conclusion that ABA-renewal requires contexts A and B to differ in several types of features, including odor cues. Recently we reported experimental evidence of the renewal of an extinguished taste aversion response in infant rats employing contexts which differ in their odor content. The present study examines the possibility of renewing an extinguished fear response in infant rats when contexts A and B do not include (Experiment 1) or include (Experiment 2) an explicit odor. Results showed absence of renewal when using standard contexts (without explicit odors, Experiment 1). However, when contexts A and B varied also in their odor content, the ABA-renewal procedure was effective in reinstating the extinguished CR (Experiment 2). Thus, it can be concluded that the sensory content of the context determines the observation of renewal in the infant rat, a result that is coherent with previous observations in the adult rat. As a whole, these results challenge our understanding of extinction as a learning process that is qualitatively different in preweanling rats than in later stages of ontogeny.