In all organisms, fear conditioning is a behavior that would be expected to be adaptive for anticipating dangerous stimuli. It therefore should have been selected for in the course of evolution. Although fear conditioning has been demonstrated in many different species, it had only been shown in one reptile group, lizards, prior to this study. We developed a paradigm to study fear conditioning in painted turtles (Chrysemys picta). In each of two experiments, there were three groups: an Experimental group in which a red light (the conditioned stimulus, or CS) was paired with a footshock (the unconditioned stimulus, or US), an Unpaired control group given unpaired presentations of the red light and footshock, and a CS Only control group presented with the red light only. The experiments differed in the number of days of training: In Experiment 1, the animals were trained for 9 days and were then run on extinction for 6 days. The results appeared to show that turtles in the Experimental group learned to stop moving when the red light came on, but this was not statistically significant. There were significant group differences during extinction, however. It appeared that the behavior was not asymptotic during acquisition, so we ran a second, longer experiment (Experiment 2) for 15 days of acquisition training and 8 or 9 days of extinction. In this experiment, the Experimental group learned to stop moving during the CS during acquisition and reversed that behavior in extinction. These results demonstrate that classical conditioning with footshock is a suitable method for studying fear learning in turtles. Further, they shed light on the evolution of fear behavior. Turtles are closely related to the stem amniotes that gave rise to both mammals and reptiles. Thus, the results demonstrate that fear conditioning is present in turtles and suggest that it was present in the stem amniote ancestors of mammals as well.
","language":"eng","license":{"name":"Creative Commons Attribution 4.0","short_name":"CC BY 4.0","text":"Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use.\r\n\r\nNo additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.","url":"https://creativecommons.org/licenses/by/4.0"},"keywords":[{"word":"reptile"},{"word":"fear learning"},{"word":"extinction"},{"word":"freezing"},{"word":"stem amiote"}],"section":"Research Article","is_remote":true,"remote_url":"https://escholarship.org/uc/item/4v21h4dc","frozenauthors":[{"first_name":"Christopher","middle_name":"","last_name":"Lau","name_suffix":"","institution":"Stony Brook University","department":"Psychology"},{"first_name":"Cassidy","middle_name":"","last_name":"Hu","name_suffix":"","institution":"Stony Brook University","department":"Psychology"},{"first_name":"Justin","middle_name":"","last_name":"Koprowski","name_suffix":"","institution":"Stony Brook University","department":"Psychology"},{"first_name":"Zachary","middle_name":"","last_name":"Lee","name_suffix":"","institution":"Stony Brook University","department":"Psychology"},{"first_name":"Aayush","middle_name":"","last_name":"Narula","name_suffix":"","institution":"Stony Brook University","department":"Psychology"},{"first_name":"Sanjana","middle_name":"","last_name":"Sankaran","name_suffix":"","institution":"Stony Brook University","department":"Psychology"},{"first_name":"Juliana","middle_name":"","last_name":"Welk","name_suffix":"","institution":"Stony Brook University","department":"Psychology"},{"first_name":"Alice","middle_name":"S.","last_name":"Powers","name_suffix":"","institution":"Stony Brook University","department":"Psychology"}],"date_submitted":"2024-11-08T21:01:45.463000Z","date_accepted":"2025-06-15T22:42:07.338000Z","date_published":"2025-07-23T14:33:00Z","render_galley":{"label":"Lau Proof 3","type":"pdf","path":"https://journalpub.escholarship.org/uclapsych_ijcp/article/39691/galley/37060/download/"},"galleys":[{"label":"Lau Proof 3","type":"pdf","path":"https://journalpub.escholarship.org/uclapsych_ijcp/article/39691/galley/37060/download/"}]}