title: Hippocampal Sharp-Wave Ripples Influence Selective Activation of the Default Mode Network.
abstract: The default mode network (DMN) is a commonly observed resting-state network (RSN) that includes medial temporal, parietal, and prefrontal regions involved in episodic memory [1-3]. The behavioral relevance of endogenous DMN activity remains elusive, despite an emerging literature correlating resting fMRI fluctuations with memory performance [4, 5]-particularly in DMN regions [6-8]. Mechanistic support for the DMN's role in memory consolidation might come from investigation of large deflections (sharp-waves) in the hippocampal local field potential that co-occur with high-frequency (>80 Hz) oscillations called ripples-both during sleep [9, 10] and awake deliberative periods [11-13]. Ripples are ideally suited for memory consolidation [14, 15], since the reactivation of hippocampal place cell ensembles occurs during ripples [16-19]. Moreover, the number of ripples after learning predicts subsequent memory performance in rodents [20-22] and humans [23], whereas electrical stimulation of the hippocampus after learning interferes with memory consolidation [24-26]. A recent study in macaques showed diffuse fMRI neocortical activation and subcortical deactivation specifically after ripples [27]. Yet it is unclear whether ripples and other hippocampal neural events influence endogenous fluctuations in specific RSNs-like the DMN-unitarily. Here, we examine fMRI datasets from anesthetized monkeys with simultaneous hippocampal electrophysiology recordings, where we observe a dramatic increase in the DMN fMRI signal following ripples, but not following other hippocampal electrophysiological events. Crucially, we find increases in ongoing DMN activity after ripples, but not in other RSNs. Our results relate endogenous DMN fluctuations to hippocampal ripples, thereby linking network-level resting fMRI fluctuations with behaviorally relevant circuit-level neural dynamics.
authors.affiliation: Wellcome Trust Centre for Neuroimaging, UCL Institute of Neurology, University College London, 12 Queen Square, London WC1N 3BG, UK; Center for Brain and Cognition, Departament de Tecnologies de la Informació I les Comunicacions, Universitat Pompeu Fabra, Roc Boronat 138, 08018 Barcelona, Spain. Electronic address: raphael.kaplan.09@ucl.ac.uk.
authors.forename: Raphael
authors.initials: R
authors.lastname: Kaplan
authors.affiliation: Center for Brain and Cognition, Departament de Tecnologies de la Informació I les Comunicacions, Universitat Pompeu Fabra, Roc Boronat 138, 08018 Barcelona, Spain.
authors.forename: Mohit H
authors.initials: MH
authors.lastname: Adhikari
authors.affiliation: Center for Brain and Cognition, Departament de Tecnologies de la Informació I les Comunicacions, Universitat Pompeu Fabra, Roc Boronat 138, 08018 Barcelona, Spain.
authors.forename: Rikkert
authors.initials: R
authors.lastname: Hindriks
authors.affiliation: Department of Health Sciences and Technology, ETH Zurich, 8057 Zurich, Switzerland; Movement Control and Neuroplasticity Research Group, KU Leuven, 3001 Leuven, Belgium.
authors.forename: Dante
authors.initials: D
authors.lastname: Mantini
authors.affiliation: Max Planck Institute for Biological Cybernetics, 72076 Tübingen, Germany.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Murayama
authors.affiliation: Max Planck Institute for Biological Cybernetics, 72076 Tübingen, Germany; Imaging Science and Biomedical Engineering, University of Manchester, Manchester M13 9PT, UK.
authors.forename: Nikos K
authors.initials: NK
authors.lastname: Logothetis
authors.affiliation: Center for Brain and Cognition, Departament de Tecnologies de la Informació I les Comunicacions, Universitat Pompeu Fabra, Roc Boronat 138, 08018 Barcelona, Spain; Institució Catalana de la Recerca i Estudis Avançats (ICREA), Universitat Pompeu Fabra, Passeig Lluís Companys 23, Barcelona 08010, Spain.
authors.forename: Gustavo
authors.initials: G
authors.lastname: Deco
mesh_terms: D000758:Anesthesia; D000818:Animals; D004558:Electric Stimulation; D006624:Hippocampus / Q000502:physiology*; D007858:Learning; D008253:Macaca mulatta / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D061212:Memory, Episodic