Temporal encoding strategies result in boosts to final free recall performance comparable to spatial ones

The method of loci is a highly effective mnemonic that recruits existing salient memory for spatial locations and uses the information as a scaffold for remembering a list of items (Yates, 1966). One possible account for the effectiveness of the spatial method of loci comes from the perspective that it utilizes evolutionarily preserved mechanisms for spatial navigation within the hippocampus (Maguire et al. in Proceedings of the National Academy of Sciences, 97(8), 4398–4403, 2000; O’Keefe & Nadel, 1978; Rodriguez et al. in Brain Research Bulletin, 57(3), 499–503, 2002). Recently, though, neurons representing temporal information have also been described within the hippocampus (Eichenbaum in Nature Reviews Neuroscience, 15(11), 732–744, 2014; Itskov, Curto, Pastalkova, & Buzsáki in The Journal of Neuroscience, 31(8), 2828–2834, 2011; MacDonald, Lepage, Eden, & Eichenbaum in Neuron, 71(4), 737–749, 2011; Mankin et al. in Proceedings of the National Academy of Sciences, 109(47), 19462–19467, 2012; Meck, Church, & Matell in Behavioral Neuroscience, 127(5), 642, 2013), challenging the primacy of spatial-based functions to hippocampal processing. Given the presence of both spatial and temporal coding mechanisms within the hippocampus, we predicted that primarily temporal encoding strategies might also enhance memory. In two different experiments, we asked participants to learn lists of unrelated nouns using the (spatial) method of loci (i.e., the layout of their home as the organizing feature) or using two novel temporal methods (i.e., autobiographical memories or using the steps to making a sandwich). Participants’ final free recall performance showed comparable boosts to the method of loci for both temporal encoding strategies, with all three scaffolding approaches demonstrating performance well above uninstructed free recall. Our findings suggest that primarily temporal representations can be used effectively to boost memory performance, comparable to spatial methods, with some caveats related to the relative ease with which participants appear to master the spatial versus temporal methods.