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Local and global oscillations as a means for neocortico-hippocampal communication| old_uid | 5291 |
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| title | Local and global oscillations as a means for neocortico-hippocampal communication |
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| start_date | 2008/09/24 |
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| schedule | 14h |
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| online | no |
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| location_info | basement seminar room (B10) |
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| details | Special Seminar |
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| summary | Brain systems communicate by means of neuronal oscillations at multiple temporal and spatial scales. The exact mechanisms by which information is represented locally and transferred between different structures of the brain are of great importance. We use large-scale recordings of local field potentials (LFP) and multiple single units in behaving rats to explore the potential mechanisms of communication between hippocampus and neocortex during different states of vigilance. Exploratory behavior and REM sleep are associated with synchronous theta rhythm in hippocampal complex. We demonstrate, that firing of neurons in different neocortical areas, including the primary somatosensory areas, parietal cortex and the prefrontal cortex, as well as local transient spatially and frequency localized gamma oscillations, are phase-locked to hippocampal theta oscillations. Slow wave sleep is associated with synchronous oscillations in the neocortex characterized by transitions of network activity from silence to bursting (DOWN-UP) recurring with ~1 Hz periodicity. The onset of the UP state in the neocortex is associated with gamma and spindle oscillations that organize local activity in the neocortex which sequentially spreads to the hippocampus via the entorhinal cortex.
Analysis of the membrane potential, unit activity and local gamma/ripple oscillations in the hippocampal network shows that hippocampal circuits are driven by the neocortical DOWN/UP state cycle, with unexpected segregation of activity in "extrinsic" EC-CA1/DG and "intrinsic" CA3-CA1 circuits to UP and DOWN states, respectively. Based on these results we propose the following mechanism of information transfer between the two structures.
During learning, the transfer of neocortical information to the hippocampus is actively initiated by the hippocampus via theta-phase biasing of neocortical networks. Conversely, during memory consolidation, the transfer of hippocampal information to the neocortex during slow wave sleep is initiated by neocortical cell assemblies activated by the DOWN-UP transition of the slow oscillation, triggering the self-organized activity in the hippocampal network. |
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| responsibles | Lawrence |
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