Work performed within this project so far have concentrated on aims 1 and 3 as specified above. As to aim 1, we succeeded in providing direct behavioral evidence that sleep favours the consolidation of abstracted, schema-like memory, using a spatial schema-learning task in rats. Notably, schema memory formation in animals sleeping after learning, was only observed with high information load during the learning phase, whereas with low information load episodic memory (for the spatial configurations of individual episodes) prevailed (Harkotte et al. 2022). In a second study regarding aim 1, contrasting sleep and wake-dependent consolidation processes, we showed that unlike wake consolidation, formation of schema memory during sleep originates from contextual hippocampal, i.e. episodic memory representations (Sawangjit et al. 2022). This study can be considered a breakthrough in the field because it demonstrated, for the first time, that in certain conditions consolidation processes during wakefulness are superior to those during sleep.
As to aim 3, we provided first evidence in rats that spatial schema-like memory can be formed already on postnatal day 16 which is distinctly earlier then it was found in other studies, with this preweaning time roughly corresponding to human infancy, < 1 yrs old. This early spatial memory formation is not only sleep-dependent but, essentially linked to activation of the medial prefrontal cortex (mPFC) areas, like the prelimbic region of the mPFC (Shan et al. 2022, Contreras et al. 2023a). We, moreover, provided first evidence suggesting that the mechanisms enabling sleep-dependent formation of abstracted schema-like memory in adults via a hippocampal-neocortical information transfer, show a rather slow, experience-driven maturation (Contreras et al. 2023b). Suggesting that an adult-like memory formation is effective not before childhood, these findings implicate that sleep-dependent memory formation during infancy is achieved through different mechanisms. This conclusion is also supported by findings from parallel studies in human children and infants (Kurz et al. 2023, Bastian et al. 2023).
