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Related Concept Videos

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Long-term depression, or LTD, is one of the ways by which synaptic plasticity—changes in the strength of chemical synapses—can occur in the brain. LTD is the process of synaptic weakening that occurs over time between pre and postsynaptic neuronal connections. The synaptic weakening of LTD works in opposition to synaptic strengthening by long-term potentiation (LTP) and together are the main mechanisms that underlie learning and memory.
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Related Experiment Video

Updated: Nov 13, 2025

The Sleep Nullifying Apparatus: A Highly Efficient Method of Sleep Depriving Drosophila
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The why and how of sleep-dependent synaptic down-selection.

Chiara Cirelli1, Giulio Tononi1

  • 1Department of Psychiatry, University of Wisconsin-Madison, 6001 Research Park Blvd, Madison, WI 53719, USA.

Seminars in Cell & Developmental Biology
|March 13, 2021
PubMed
Summary

Sleep is essential for renormalizing brain synaptic weights, preventing saturation and enabling new learning. This process involves specific synaptic down-selection during sleep, crucial for cognitive function.

Keywords:
Cerebral cortexHippocampusNREM sleepREM sleep

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Area of Science:

  • Neuroscience
  • Sleep Science
  • Molecular Biology

Background:

  • Sleep involves disconnecting from the environment, posing risks.
  • A critical brain function must justify daily sleep.
  • This function likely depends on the brain being in an offline state.

Purpose of the Study:

  • To investigate the essential function of sleep.
  • To test the hypothesis that sleep renormalizes synaptic weights.
  • To understand the mechanisms of sleep-dependent synaptic plasticity.

Main Methods:

  • Review of molecular, electrophysiological, and ultrastructural evidence.
  • Analysis of synaptic strength changes after wake and sleep phases.
  • Identification of molecular mechanisms for synaptic weakening during sleep.

Main Results:

  • Evidence shows a net increase in synaptic strength after wakefulness.
  • A net decrease in synaptic strength is observed after sleep.
  • A molecular mechanism enabling broad synaptic weakening during sleep has been identified.

Conclusions:

  • Sleep serves to renormalize synaptic weights, preventing energetic overload and saturation.
  • Sleep-dependent synaptic down-selection is a specific process that benefits cognition.
  • While the occurrence and purpose of synaptic down-selection during sleep are established, the precise mechanisms are still under investigation.