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We reporta human electrophysiological brain state that predicts successful memory for events before they occur. Using magnetoencephalographic recordings of brain activity during episodic memory encoding, we show that amplitudes of theta oscillations shortly preceding the onsets of words were higher for laterrecalled than for later-forgotten words. Furthermore, single-trial analyses revealed that recall rate in all 24 participants tested increased asa function of increasing prestimulus theta amplitude. This positive correlation was independent of whether participants were preparing for semantic or phonemic stimulus processing, thus likely signifying a memory-related theta state rather than a preparatory task set. Source analysis Iocated this theta state to the medial temporal Iobe, a region known to be critical for encoding and recall. These findings provide insight into state-related aspects of memory formation in humans, and open a perspective for improving memory through theta-related brain states. hippocampus | magnetoencephalography | memory | oscillations| prestimulus

Byline: Andras Szentkuti (1), Sebastian Guderian (1), Kolja Schiltz (1), Jorn Kaufmann (1), Thomas F. Munte (2), Hans-Jochen Heinze (1), Emrah Duzel (1) Keywords: Hippocampus; aging; volumetry; MR-spectroscopy; voxel based morphometry; diffusion weighted imaging Abstract: Abstract The age-related structural changes of the human hippocampus are not entirely understood. The goal of the present investigation was to understand better the nature of age-related hippocampal changes by a comparative MR-analysis of four complementary aspects of hippocampal integrity: total volume, metabolite concentration, neuron to glial cell ratio and amount of extracellular diffusion space for water. To that end, we applied MR-based methods of manual and computerized (voxel-based morphometry) volumetry, diffusion-weighted imaging and 1.sup.H MR spectroscopy to characterize specific age-related hippocampal effects in a group of 22 healthy old adults in comparison with a group of 13 healthy younger adults. Age-related reductions of the hippocampal N-acetyl aspartate to creatine/choline ratio together with only marginal age-related reductions in hippocampal volumes and increases in diffusion parameters suggest that the process of aging affects mainly the metabolic status of the hippocampus with little equivalent age-related changes in hippocampal cell density. The metabolic changes are unspecific as they are not restricted to the hippocampus but equally occur in measures obtained from extrahippocampal temporal lobe regions. Author Affiliation: (1) Dept. of Neurology II, Otto-von-Guericke University, Leipziger Str. 44, 39120, Magdeburg, Germany (2) Dept. of Neuropsychology, Otto-von-Guericke University, Magdeburg, Germany Article History: Registration Date: 01/01/2004 Received Date: 15/12/2003 Accepted Date: 17/05/2004