F O C U S E D R E V I E W Edited by: Carmen Sandi, Ecole Polytechnique Fédérale de Lausanne, Switzerland Reviewed by: Bruno Poucet, CNRS and Université de Provence, France Alexander Dityatev, Italian Institute of Technology, Italy †Correspondence: Denise Manahan-Vaughan completed her doctoral degree at Trinity College Dublin and started her research career in Germany in the mid 90’s. She is Chair of the Department of Neurophysiology at the Medical Faculty of the RUB. Currently she is a member of the executive committee of the Federation of European Neuroscience Societies and chair of the Network of European Neuroscience Schools. Her research focusses especially on studies of the role of hippocampal synaptic plasticity in memory processes, using a combined in vivo electrophysiological, behavioural and molecular methodological approach. denise.manahan-vaughan@ rub.de Relationship of hippocampal theta and gamma oscillations to potentiation of synaptic transmission Arthur Bikbaev1 and Denise Manahan-Vaughan1,2,† 1 Department of Experimental Neurophysiology, Medical Faculty, Ruhr University Bochum, Bochum, Germany. 2 International Graduate School of Neuroscience, Ruhr University Bochum, Bochum, Germany. In the hippocampus in vivo, both synaptic plasticity and network activity are closely interdependent. We have found that immediately after an attempt to induce long-term potentiation (LTP), changes in theta (5–10 Hz) and gamma (30–100 Hz) activity correlate tightly with the occurrence of LTP, suggesting that tetanisation-driven activation of sensory inputs synchronises the activity of granule cells and interneurons, and thus, facilitates the encoding of acquired stimuli. This results in increase of theta and gamma power, and elevates the probability that afferent stimuli both coincide with the peak of theta cycle and reach their post-synaptic target within the gamma time-window (of 10–30 ms). Both these mechanisms can effectively shift the direction, of tetanisation-induced changes in synaptic weight, towards potentiation and induction of LTP. Here, we discuss our ﬁndings in the context of possible mechanisms that link theta and gamma oscillations with LTP induction, as well as their role in information processing and formation of memories. Keywords: LTP, theta, gamma, network activity, oscillations, synaptic plasticity, tetanisation, in vivo LONG-TERM POTENTIATION OF SYNAPTIC TRANSMISSION AS A MODEL OF SYNAPTIC PLASTICITY The ability to analyse and learn new information and, if necessary, modify ongoing behaviour, based on a combination of previous and recent memories, is an important factor for the survival of organisms in an ever-changing world. Creating and managing these memory traces, comprise core functions of the central nervous system, which rely on its ability to engage in synaptic plasticity. They can be monitored at different levels, ranging from the subcellular to the behavioural. Since its discovery in the late 1960s (Andersen and Lømo, 1967; Bliss and Lømo, 1973; see for review: Lømo, 2003), long-term potentiation (LTP) has been the subject of intense study, using a plethora of induction protocols, species, and various preparations both in vivo and in vitro. Nowadays, LTP, along with long-term depres- sion (LTD), is widely used as a model of synaptic information storage and are believed to represent the processes of learning and memory in neuronal networks (Abraham, 2003; Bear, 1996; Bliss and Collingridge, 1993; Kemp and Manahan-Vaughan, 2007; Lynch, 2004; Whitlock et al., 2006). Synaptic plasticity in the form of LTP, typically results in both functional and structural reorgani- sation of the synapse, that evolves over time and comprises different phases, namely LTP-induction (post-tetanic potentiation), short-term potentia- tion, LTP expression (early LTP) and maintenance (late LTP) (Abraham, 2003; Bliss and Collingridge, 1993; Frey et al., 1993; Huang et al., 1996; Nguyen et al., 1994). Furthermore, each of these phases is characterised by the different involvement of neuro- 56 | July 2008 | Volume 2 | Issue 1 www.frontiersin.org