Hippocampal sharp wave-ripple: A cognitive biomarker for episodic memory and planning

György Buzsáki
2015 Hippocampus  
Sharp wave ripples (SPW-Rs) represent the most synchronous population pattern in the mammalian brain. Their excitatory output affects a wide area of the cortex and several subcortical nuclei. SPW-Rs occur during "off-line" states of the brain, associated with consummatory behaviors and non-REM sleep, and are influenced by numerous neurotransmitters and neuromodulators. They arise from the excitatory recurrent system of the CA3 region and the SPW-induced excitation brings about a fast network
more » ... illation (ripple) in CA1. The spike content of SPW-Rs is temporally and spatially coordinated by a consortium of interneurons to replay fragments of waking neuronal sequences in a compressed format. SPW-Rs assist in transferring this compressed hippocampal representation to distributed circuits to support memory consolidation; selective disruption of SPW-Rs interferes with memory. Recently acquired and pre-existing information are combined during SPW-R replay to influence decisions, plan actions and, potentially, allow for creative thoughts. In addition to the widely studied contribution to memory, SPW-Rs may also affect endocrine function via activation of hypothalamic circuits. Alteration of the physiological mechanisms supporting SPW-Rs leads to their pathological conversion, "p-ripples," which are a marker of epileptogenic tissue and can be observed in rodent models of schizophrenia and Alzheimer's Disease. Mechanisms for SPW-R genesis and function are discussed in this review. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. in Wiley Online Library (wileyonlinelibrary. com). Ripple events (or ripples) consist of a series of ripple waves (typical range 3-9) Ripple events are described by magnitude (expressed as amplitude or power mV 2 ), duration (ms), number of ripple waves per event, intra-ripple frequency (Hz), probability of occurrence (or incidence; number per second) and inter-ripple event intervals (ms) Ripple/SPW-R cluster or ripple burst refers to temporally close ripple/SPW-R events comments on various parts of the manuscript.
doi:10.1002/hipo.22488 pmid:26135716 pmcid:PMC4648295 fatcat:kmeessu4pbc27lungr5ynewbf4