Adolescent rats exhibit impaired extinction retention compared to pre-adolescent and adult rats. A single nonreinforced exposure to the conditioned stimulus (CS; a retrieval trial) given shortly before extinction has been shown in some circumstances to reduce the recovery of fear after extinction in adult animals. This study investigated whether a…

In this reprint of a seminal article, once considered quite controversial, the authors discuss their radical claim that rats laugh. Even more provocative, the authors found that this rat-joy sound, especially evident during play, could be amplified dramatically by what they formally call heterospecific (cross-species) handplay (tickling). The…