Faculty » Sara Mednick
A classic question in memory literature is: how does the human brain learn new information while not overwriting previously stored memories? Memory models solve this so-called stability plasticity dilemma by proposing a post-encoding period of reduced interference that allows the brain to consolidate recent experience into long-term storage. A growing body of research shows that for some types of memory, consolidation takes place during sleep. Recent studies show that rapid eye movement (REM) sleep enhances performance from baseline and promotes generalization in non-declarative memory tasks, whereas non-REM (NREM) sleep decreases forgetting from baseline on declarative memory tasks. These different performance profiles suggest that two different mechanisms exist for consolidating declarative and non-declarative memories. Declarative memory traces must be protected from interference from other memories, whereas non-declarative memories, almost by definition, form by association between different memory traces. In the case of declarative memory, association is synonymous with interference, and in the case of non-declarative memory, it is synonymous with plasticity. For example, NREM may help you remember the exact dates of the second Iraq War, a declarative memory trace that should not get confused with dates of other wars in history. In contrast, REM sleep may help you relate reasons for entering the Iraq war to other wars in history, which will shape your views about war in general. Thus, instead of reducing interference, the brain may need to control interference depending on whether memories are declarative or non-declarative. I propose that optimal conditions for reducing interference and protecting declarative memories occur during NREM, whereas optimal conditions for increasing interference and enhancing non-declarative memories occur during REM.
My research investigates underlying differences between declarative and non-declarative memories by studying REM-driven and NREM-driven consolidation processes. My approach is unique in using naps and pharmacology as tools. In contrast with nighttime sleep, nap studies: 1) eliminate circadian confounds; 2) have appropriate controls (wake or quiet rest); 3) allow titration of sleep stages by modulating the duration and time of day of the nap; and 4) have compelling translational applications, e.g. pilots, students, surgeons, soldiers. Importantly, my studies show that napping produces the same sleep-stage-specific enhancements as overnight sleep. I utilize electroencephalography (EEG), functional magnetic resonance imaging (fMRI), pharmacology, psychophysics, and sleep, in collaborations with researchers from a wide range of disciplines including, development, political science, memory, vision, sleep, computer modeling, and psychopharmacology.
- Mednick SC, Cai D, Anagnostaros S, Shuman T, Wixted J, An Opportunistic Theory of Cellular and Systems Consolidation. Trends in Neuroscience Jul 2011.
- Mednick SC, Christakis NA, Fowler JH The Spread of Sleep Loss Influences Drug Use in Adolescent Social Networks. PLoS ONE 5: e9775 (2010).
- Cai D, Mednick SA, Kanady J, Drummond SPA, Mednick SC, Priming Associative Networks: REM, Not Incubation, Improves Creativity. Proceedings from the National Academy of Sciences USA June (2009).
- Mednick SC, Kanady J, Cai D, Drummond SPA, Comparing the benefits of Caffeine, Naps and Placebo on Verbal, Motor, and Perceptual Memory. Behavioral Brain Research, 193 (2008) 79–86.
- Mednick SC, Arman AC, Boynton GM, “The time course and specificity of perceptual deterioration” Proceedings from the National Academy of Sciences USA 2005 Mar 8;102(10):3881-5. Epub 2005 Feb 24.
- Mednick SC., Nakayama K., Stickgold R. “Sleep-dependent Learning: A Nap is as Good as a Night,”Nature Neuroscience, July 2003.
- Mednick SC, Nakayama K, Cantero JL, Atienza M, Levin AA, Pathak N, Stickgold R, “The Restorative Benefit of Naps on Perceptual Deterioration,” Nature Neuroscience, July 2002.