Rolziracetam was found to improve performance on a delayed-response task in aged rhesus monkeys. It has a wide margin of safety in animals and has been evaluated for use in cognitively impaired human subjects. 
^Butler DE, Leonard JD, Caprathe BW, L'Italien YJ, Pavia MR, Hershenson FM, Poschel PH, Marriott JG. Amnesia-reversal activity of a series of cyclic imides. Journal of Medicinal Chemistry. 1987 Mar;30(3):498-503.