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Abstract

Experimental work in animals and humans suggests that various oscillatory patterns, including single or multiple cycle short-lasting episodes, reflect state-changes in self-organizing largescale networks. For instance, patterns like K-complexes, spindles, hippocampal sharp wave ripples, and PGO waves, are thought to reflect state-changes in networks regulating cognitive capacities, such as learning, memory encoding and consolidation, and memory-guided decision making . Although studied in detail with neurophysiological methods, the global effects of the aforementioned events on the entire brain remained elusive. The use of multishankmultichannel (MS-MC) electrical recordings of activity in different structures per se permits both the detection and the contextual identification of structure-specific neural events, for that matter also of their interrelationships. Combining MS-MC recordings with spatiotemporally resolved fMRI evidently oଏers a unique opportunity to study the cooperative patterns of a large number of brain structures either leading or responding to recorded events. In an effort to do so, we developed so-called neural event triggered fMRI (NET-fMRI), and used it to study the dynamics of the networks related to ripples and PGO events. Initial recordings in hippocampus with ripple-triggered functional magnetic resonance imaging, showed that most of the cortex is selectively activated during the ripples, whereas most diencephalic, midbrain and brainstem regions are strongly inhibited [3]. Other regions, such as the parabrachial nucleus in pons were up or down-modulated and so were the low frequency field potentials in the peri-event intervals. Analysis of the temporal alignment between the SPW and ripple components revealed well-diଏerentiated SPW-R subtypes in the CA1 LFP . Well defined PGO-subtypes were also evident in pons, with phasic events often occurring together with ripples and brief oscillations occurring exclusively in REM periods characterized by high hippocampal theta activity. The co-occurrence of ripples and PGO waves is the first evidence for a sequential occurrence of synaptic tagging and local plasticity changes potentially induced by the cholinergic PGO activity, that is related to synaptic consolidation. In the talk I will present new results related to such event interactions, and the global NET-fMRI patterns associated with them.