Sleep restores the body and brain. To understand the restorative effects of sleep on neuronal firing, Hiroyuki Miyawaki, a postdoctoral scholar in Kamran Diba’s Neural Circuits & Memory lab implanted electrodes in the hippocampus and observed neuronal firing patterns from hundreds of individual neurons over multiple waking and sleep cycles. In a study recently published in journal Current Biology, he found that sleep serves to decrease neuronal firing rates by an average of 11% per hour sleep, translating into significant energy savings over time. Surprisingly, these firing decreases were predicted by the incidence rates of spindle and fast ripple oscillations. There is evidence that these fast oscillations can change the strength of synaptic connections between neurons. Thus, the findings suggest that sleep serves to restore the brain by decreasing the strength of connections between neurons, leading to decreased energy expenditure and a more efficient memory circuit. Interestingly, the network changes only occurred following epochs of REM (rapid eye movement) sleep, further suggesting that REM sleep is required to incorporate plastic changes over sleep.