Hippocampal sharp wave bursts coincide with neocortical "up-state" transitions.
The sleeping neocortex shows nested oscillatory activity in different frequency ranges, characterized by fluctuations between "up-states" and "down-states." High-density neuronal ensemble recordings in rats now reveal the interaction between synchronized activity in the hippocampus and neocortex: Electroencephalographic sharp waves in the hippocampus were more probable during down-states than during up-states, and tended to coincide with transitions from down-states to up-states. The form of cortical activity fluctuations and their interactions with sharp waves depend on sleep depth: In deeper sleep stages, characterized by strong neocortical oscillation in the delta range or slower (approximately 0.8-4 Hz), sharp-wave-triggered peri-event time histograms (PETH) are consistent with a longer duration for down-states than for up-states. In lighter sleep, the sharp-wave-triggered PETH suggested longer up-states than down-states. These results highlight the interplay in the hippocampal/neocortical loop: Decreased neocortical input during down-states may be a factor in generation of sharp waves. In turn, sharp waves may facilitate down-to-up transitions. This interplay may reflect joint memory trace reactivation in the hippocampus and in the neocortex, possibly contributing to consolidation of long-term memory: Off-line reactivation of recent neural activity patterns in the hippocampus occurs during 50-100-msec electroencephalographic sharp waves, corresponding to pyramidal-cell population bursts. The neocortical up-states starting in correspondence with sharp waves may be influenced by the reactivated information carried by the hippocampal sharp wave.
Battaglia
Francesco P
FP
Arizona Research Laboratories--Division of Neural Systems, Memory, and Aging, University of Arizona, Tucson, Arizona 85724, USA.
Sutherland
Gary R
GR
McNaughton
Bruce L
BL
D000818:Animals; D003344:Cortical Synchronization; D004569:Electroencephalography; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D019579:Neocortex / Q000166:cytology / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D051381:Rats; D012890:Sleep / Q000502:physiology*