Amazing stuff! Solving the mysteries of human memory.
"... The hippocampus is divided into three regions: CA1, CA2 and CA3. CA1 and CA3 are involved in encoding memories related to time and space and, are well-studied; less is known about CA2, which the current study found generates this silencing and resetting of the hippocampus during sleep. ..."
From the Perspective abstract:
"Sleep is not just a time for the body to rest but also for the mind to solidify memories. During the non-rapid eye movement (NREM) phase of sleep, neurons in the hippocampus display short bursts of firing activity called sharp-wave ripples (SWRs), which is essential for memory consolidation. How the brain rebalances its activity after these bursts remains unclear. ... Karaba et al. ... report a new type of neuron activity in the rodent hippocampus that is characterized by long episodes of neuronal firing called barrage of action potentials (BARR). BARRs counteract SWRs to suppress the increased activity of neurons involved in learning during NREM sleep. The findings demonstrate that BARRs are crucial for memory consolidation by modulating memory reactivation and help to reconcile different theories on the role of sleep for memory formation."
From the editor's summary and abstract:
"Editor’s summary
During sleep, there is an increase in the coordinated firing of neuronal ensembles that were previously active during behavior. These hippocampal sharp-wave ripples are necessary for sleep-dependent memory consolidation. However, how the hippocampus regulates such increases in ensemble reactivation and synchrony while keeping the overall homeostatic balance of the network is not known. Karaba et al. discovered a new type of network pattern, a barrage of activity, that originated in hippocampal area CA2 and involved pyramidal cells and a specific type of interneurons. This barrage had differential effects on the efferent CA1 neurons and was dependent on experience. Optogenetic manipulations of this activity indicated its role in different tasks. Unlike sharp-wave ripples, which increase hippocampal output, this barrage decreased the output, thereby rebalancing the network.
Abstract
Memory consolidation involves the synchronous reactivation of hippocampal cells active during recent experience in sleep sharp-wave ripples (SWRs). How this increase in firing rates and synchrony after learning is counterbalanced to preserve network stability is not understood. We discovered a network event generated by an intrahippocampal circuit formed by a subset of CA2 pyramidal cells to cholecystokinin-expressing (CCK+) basket cells, which fire a barrage of action potentials (“BARR”) during non–rapid eye movement sleep. CA1 neurons and assemblies that increased their activity during learning were reactivated during SWRs but inhibited during BARRs. The initial increase in reactivation during SWRs returned to baseline through sleep. This trend was abolished by silencing CCK+ basket cells during BARRs, resulting in higher synchrony of CA1 assemblies and impaired memory consolidation."
A BARRage of firing while asleep (no public access)
A hippocampal circuit mechanism to balance memory reactivation during sleep (no public access)
No comments:
Post a Comment