Human relational memory requires time and sleep

Abstract

Relational memory, the flexible ability to generalize across existing stores of information, is a fundamental property of human cognition. Little is known, however, about how and when this inferential knowledge emerges. Here, we test the hypothesis that human relational memory develops during offline time periods. Fifty-six participants initially learned five ''premise pairs'' (A>B, B>C, C>D, D>E, and E>F). Unknown to subjects, the pairs contained an embedded hierarchy (A>B>C>D>E>F). Following an offline delay of either 20 min, 12 hr (wake or sleep), or 24 hr, knowledge of the hierarchy was tested by examining inferential judgments for novel ''inference pairs'' (B>D, C>E, and B>E). Despite all groups achieving near-identical premise pair retention after the offline delay (all groups, >85%; the building blocks of the hierarchy), a striking dissociation was evident in the ability to make relational inference judgments: the 20-min group showed no evidence of inferential ability (52%), whereas the 12-and 24-hr groups displayed highly significant relational memory developments (inference ability of both groups, >75%; P < 0.001). Moreover, if the 12-hr period contained sleep, an additional boost to relational memory was seen for the most distant inferential judgment (the B>E pair; sleep ‫؍‬ 93%, wake ‫؍‬ 69%, P ‫؍‬ 0.03). Interestingly, despite this increase in performance, the sleep benefit was not associated with an increase in subjective confidence for these judgments. Together, these findings demonstrate that human relational memory develops during offline time delays. Furthermore, sleep appears to preferentially facilitate this process by enhancing hierarchical memory binding, thereby allowing superior performance for the more distant inferential judgments, a benefit that may operate below the level of conscious awareness.association ͉ inference ͉ learning ͉ offline

Overlapping memory replay during sleep builds cognitive schemata

“…It explains why newly learned material becomes increasingly easy to integrate and remember as a conceptual schema takes shape [18,19]. It also explains the observed postsleep enhancements in integration [6][7][8], abstraction [1][2][3][4][5], insight [9] and false memory formation [28].…”

“…In considering this issue we should note that the behavioural studies of integration [6][7][8], abstraction [1][2][3][4][5], insight [9] and false memory formation [28] discussed above all suggest that sleep facilitates the formation of connections between related items. Importantly, performance on these tasks typically improves across both wakefulness and sleep but improvement is greater across the latter.…”

“…Recent work has demonstrated a role for sleep in improved integration [6][7][8], insight [9], and false memory formation [28]. iOtA provides a common mechanism for all of these effects.…”

“…iOtA provides a common mechanism for all of these effects. In one integration paradigm [6], participants implicitly learned a hierarchy of abstract images with the structure A > B > C > D > E > F. During training with feedback they were shown adjacent images from this hierarchy (e.g. B/C and C/D) and they were asked to indicate which was higher (>).…”

“…Central shared concepts of this type can be thought of as the 'gist' (see Glossary), or essential features, of a set of memories, and taken together can form a cognitive framework of expectations or schema (Box 1). This article proposes a physiological mechanism by which memory replay during sleep could be responsible for the abstraction of gist information from newly encoded memories to form cognitive schemata.Recent research has shown that sleep facilitates abstraction of gist information [1][2][3][4][5] as well as integration across multiple memories [6][7][8], insight into hidden solutions [9], and even the ability to make creative connections between distantly related ideas and concepts [10]. These findings build upon a strong body of work demonstrating that sleep plays a crucial role in memory consolidation (for reviews [11][12][13]), as well as a highly influential model of how memories are re-organised and strengthened by replay during slow wave sleep (SWS) (see [11,12,[14][15][16][17] and Box 2).…”