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Unformatted text preview: Human relational memory requires time and sleep Jeffrey M. Ellenbogen* , Peter T. Hu*, Jessica D. Payne*, Debra Titone , and Matthew P. Walker* *Sleep and Neuroimaging Laboratory, Department of Psychiatry, Beth Israel Deaconess Medical Center, and Departments of Neurology and Medicine (Sleep Division), Brigham and Womens Hospital, Harvard Medical School, Boston, MA 02115; and Department of Psychology, McGill University, 1205 Doctor Penfield Avenue, Montreal, QC, Canada H3A 1B1 Edited by Edward E. Smith, Columbia University, New York, NY, and approved March 2, 2007 (received for review January 5, 2007) 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 rela- tional memory develops during offline time periods. Fifty-six partic- ipants 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 testedbyexamininginferentialjudgmentsfornovelinferencepairs (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 judg- ments. Together, these findings demonstrate that human relational memory develops during offline time delays. Furthermore, sleep appears to preferentially facilitate this process by enhancing hierar- chical 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 T he capacity to flexibly interrelate existing stores of knowledge isafundamentalpropertyofhigherlearningandonethatallows us to make innovative memory decisions in novel situations (1). For example, when studying the United States highway system for the first time, if you learn that you can travel south on route 95 from Boston to New York and that you can also travel south on route 95 fromNewYorktoWashington,DC,youcouldinterrelatethesetwo...
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