gamma amplitude is highest, hence resulting in the strengthening of the activated synaptic pathway. The outcomes of studies of spike-timing depend- ent plasticity (see for review: Dan and Poo, 2004) demonstrate that such synchronisation of neuronal spiking, within a 10–30 ms window: which precisely matches to a single gamma cycle, can dramatically increase the probability of potentiation of activated synaptic connections. Moreover, in in vitro record- ings from the primary visual cortex, where theta activity is generally not so prominent as in the hip- pocampus, pairing the stimuli with either the peak or trough of oscillations in the beta and gamma fre- quency ranges has been found to effectively drive synaptic plasticity towards potentiation or depres- sion, respectively (Wespatat et al., 2004). In this context,one can conclude that the transient enhancement of theta and gamma oscillations in the post-tetanisation period reﬂects the engagement of the system in encoding of acquired information. This can result in a subsequent “reconﬁguration” of the network, coupled with the strengthening of currently activated connections, and the weakening of the others. Furthermore, facilitated theta activ- ity can support a tighter timing control of the ﬁring of principal cells and interneurons in the network, which serves to optimise information processing. Tetanisation-triggered enhancement of gamma oscillations is associated, on the other hand, with higher synchronisation and reﬂects the coordinated ensemble activity aimed to encode/retrieve relevant memories. Accordingly, the absence or inconsist- ency of such changes in network activity can be related to the lack, or insufﬁciency, of activation of required neurotransmitter systems, sub-optimal conditions for the processing of sensory informa- tion and, therefore, a lower probability for LTP. Hippocampal oscillations are linked to LTP is engaged in the acquisition and processing of sensory stimuli, which can lead in turn to experi- ence-based modiﬁcation of ongoing behaviour. Gamma oscillations were also proposed to play a role in various cognitive processes both in human and animals. At the neuronal level, the acquisition and formation of memory traces are believed to rely on activity-related changes in synaptic efﬁcacy, and LTP of synaptic transmission after patterned afferent stimulation is considered as an adequate experimental model of these processes. However, despite the existence of extensive experimental data showing the involvement of hippocampal theta and gamma oscillations in cognitive processes, a relationship between the coordinated enhance- ment of both theta and gamma power immediately after tetanisation and the consequences of induc- tion of synaptic plasticity in freely moving rats was not, to our knowledge, described earlier. We found that changes in theta and gamma oscillatory activ- ity precede electrically induced potentiation of synaptic transmission. Importantly, the correlated tetanisation-driven enhancement of both theta and gamma oscillations is associated with successful short- and LTP, but not with its failure. These ﬁnd- ings link LTP with the oscillatory activity of rather large assemblies of hippocampal principal cells and interneurons, and provide additional support for the role of hippocampal theta and gamma oscilla- tions in information processing and the formation of new memories. CONFLICT OF INTEREST STATEMENT The authors declare that the research was conducted in the absence of any commercial or ﬁnancial rela- tionships that could be construed as a potential conﬂict of interest. SUMMARY For several decades, theta rhythm was regarded in rodents as an electrographic hallmark of exploratory behaviour, that occurs when the hippocampus ACKNOWLEDGEMENT This work was supported by a Deutsche Forschungsgemeinschaft grant to D. Manahan- Vaughan (Ma1843). REFERENCES Abraham, W. C. (2003). How long will long-term potentiation last? Philos. Trans. R. Soc. Lond., B, Biol. Sci. 358, 735–744. Abraham, W. C., Dragunow, M., and Tate, W. P. (1991). The role of immediate early genes in the stabilisation of long-term potentiation. Mol. Neurobiol. 5, 297–314. Abraham, W. C., and Mason, S. E. (1988). Effects of the NMDA receptor/channel antagonists CPP and MK801 on hippocampal ﬁeld potentials and long-term potentiation in anesthetized rats. Brain Res. 462, 40–46. 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