This painting, Trett (Tired. 1885) by Christian Krohg, portrays a woman who appears to have fallen asleep while working. Sleep is essential for maintaining cognitive performance, but the functions of sleep at the neural level are still debated. In this issue, Gina Poe discusses evidence that sleep is for forgetting (464–473) and Susan Sara presents evidence that sleep is for remembering (457–463). Public domain image found on Wikimedia Commons at https://commons.wikimedia.org/w/index.php?curid=29841752.