Why does sleeping on it help? New research from the University of Bristol examines how brain activity during sleep sorts the vast stream of daily experiences, preserving only the most important information in lasting memory.
Researchers from the Centre for Synaptic Plasticity at the University of Bristol report findings that strengthen the case for the cognitive benefits of a good night’s sleep. Poor sleep is common not only among the general population but also among people with conditions such as schizophrenia or Alzheimer’s disease, and disrupted sleep is associated with reduced mental function and learning difficulties.
The study, published in the journal Cell Reports and discussed in Trends in Neuroscience, shows that patterns of brain activity experienced during waking are replayed at accelerated speed during subsequent sleep. This replay takes place in the hippocampus, the brain’s central memory filing system.
The key discovery is that replayed activity during sleep strengthens the tiny connections between active nerve cells — a process known as synaptic plasticity — which is essential for consolidating memory. By selectively replaying particular daytime activity patterns, sleep effectively filters and stores information that is most important to retain.
Lead researcher Dr. Jack Mellor, from the School of Physiology, Pharmacology and Neuroscience, explained: “These results reveal fundamental processes that occur in the brain as memories are consolidated during sleep. Our data also indicate that the success of activity replay during sleep depends in part on the learner’s emotional state while acquiring information. This has significant implications for how we teach and support effective learning.”
Funding: The study was carried out by the University of Bristol’s Centre for Synaptic Plasticity within the School of Physiology, Pharmacology & Neuroscience, and received support from the Medical Research Council (MRC), the Wellcome Trust, the Engineering and Physical Sciences Research Council (EPSRC) and Eli Lilly & Co.
The research places its findings in the context of related work, including:
Memory trace replay: the shaping of memory consolidation by neuromodulation by Atherton, L.A., Dupret, D. & Mellor, J.R. (2015) in Trends in Neuroscience, 38, 560–570.
Decoupling of sleep-dependent cortical and hippocampal interactions in a neurodevelopmental model of schizophrenia by Phillips, K.G., Bartsch, U., McCarthy, A.P., Edgar, D.M., Tricklebank, M.D., Wafford, K.A. & Jones, M.W. (2012) in Neuron, 76, 526–533.
Source: University of Bristol
Image credit: Adapted from the University of Bristol press release.
Original research: Full open access research: “Sharp-Wave Ripples Orchestrate the Induction of Synaptic Plasticity during Reactivation of Place Cell Firing Patterns in the Hippocampus” by Sadowski, J.H.L.P., Jones, M.W. and Mellor, J.R., published in Cell Reports (published online January 19, 2016; doi:10.1016/j.celrep.2016.01.061).
Abstract
Sharp-Wave Ripples Orchestrate the Induction of Synaptic Plasticity during Reactivation of Place Cell Firing Patterns in the Hippocampus
• Reactivated place cell firing patterns can induce long-term potentiation (LTP) in the hippocampus.
• Sharp-wave ripples (SWRs) are required for the induction of LTP.
• Dendritic depolarization that accompanies sharp-wave ripples is necessary for LTP.
• The precise timing of place cell firing within sharp-wave ripples controls whether LTP is induced.
Summary
Place cell firing patterns that are reactivated during hippocampal sharp-wave ripples (SWRs) in rest or sleep are believed to trigger synaptic plasticity and promote consolidation of recently encoded information. Until now, the ability of naturally reactivated spike trains to induce plasticity had not been directly demonstrated. This study shows that place cell firing patterns recorded simultaneously from CA3 and CA1 regions of the rat dorsal hippocampus can produce long-term potentiation at CA3–CA1 synapses, but only when SWR-associated synaptic activity produces the dendritic depolarization needed for plasticity. Furthermore, the exact timing of coincident CA3 and CA1 spikes relative to SWR onset is critical for inducing LTP and can predict the plasticity resulting from reactivation. These findings support an essential role for sharp-wave ripples in initiating and tuning the plasticity processes that underlie memory consolidation during rest and sleep.
“Sharp-Wave Ripples Orchestrate the Induction of Synaptic Plasticity during Reactivation of Place Cell Firing Patterns in the Hippocampus” by Sadowski, J.H.L.P., Jones, M.W. and Mellor, J.R., Cell Reports, published online January 19, 2016 (doi:10.1016/j.celrep.2016.01.061).