The article says leptin, produced in the brain to tell us when to stop eating, also boosts memory. Eating also produces a satisfied feeling, and there"s a particular kind of satisfaction one feels after stopping eating for the time being, that one doesn"t feel while eating. Could this particular after-eating feeling of satisfaction be due not only to a rise in blood sugar level, and the energy derived from sugar, but could it also have evolved as a way to help the brain to improve its memory of the events that preceded eating the food, as a way of imprinting on the brain that whatever it had just done, it had culminated in successfully acquiring food, and memory of those events was important to doing it again? In fact, I wonder if leptin might actually be more responsible for what we normally have thought of as a sugar rush, than the action of the sugar itself. Another aspect of after-eating satisfaction is that, for the moment, you don"t need to defend yourself from having your food stolen by others (at least in an earlier stage of our evolution), and so you can relax, and that"s worthy of another release of either leptin or other things, as a reward and a way of helping you remember what you did to prevent your food from being stolen.