Infant rats can acquire,but not retain contextual associations in object-in-context and contextual fear conditioning paradigms

Context learning in postnatal day (PD) 16–18 rats has been taken by Revillo, Cotella, Paglini, and Arias (2015, Physiology & Behavior, 148 , 6–21) to challenge the view that the ontogeny of contextual learning is related to the development of the hippocampal system (Rudy, 1993, Behavioral Neuroscience, 107 (5), 887–891; Schiffino, Murawski, Rosen, & Stanton, 2011 Neurobiology of Learning and Memory, 95 (2), 190–198). Whether context learning is “incidental” or “reinforcement-driven” may determine the ontogeny and neural systems involved (Rudy, 2009, Learning & Memory (Cold Spring Harbor, N.Y.), 16 , 573–585). However, we have shown differential ontogeny of two different forms of incidental context learning, the context pre-exposure facilitation effect (CPFE; Jablonski, Schiffino, & Stanton, 2012, Developmental Psychobiology, 54 (7), 714–722), which emerges between PD 17 and 21; and object-in-context recognition (OiC, Ramsaran, Westbrook, & Stanton, 2016, Developmental Psychobiology, 58 (7), 883–895; Ramsaran, Sanders, & Stanton, 2016, Behavioural Brain Research, 298 , 37–47), which is present on PD17. We investigated whether this task-dissociation reflects an encoding or a retention deficit, by varying the sample-to-testing intervals for both tasks. Experiment 1A found that PD17 rats were able to perform the OiC task after short (5 min) but not long (24 hr) sample-to-test intervals. Experiments 1B and 1C found that PD17 rats trained on the CPFE are able to acquire and express context-shock associations after short but not long retention intervals. These findings suggest that pre-weanling rats encode contexts but show poor consolidation or retrieval after longer retention intervals.