Hippocampal ripples down-regulate synapses

Rebalancing mechanisms during sleep Synapses are often strengthened during wake periods and thus need to be homeostatically readjusted during sleep. During slow-wave sleep, synaptic depression is dominant. Sharp wave and ripple events are transient high-frequency field oscillations that occur spontaneously during slow-wave sleep in the brain. Norimoto et al. found that these events induced long-term depression of hippocampal synapses and may thus help to refine recently acquired memories (see the Perspective by Draguhn). Science , this issue p. 1524 ; see also p. 1461