Appetitive memory with survival benefit is robust across aging in Drosophila

Abstract

The formation of memory declines with advancing age. However, susceptibility to memory impairments depends on several factors, including the robustness of memory, the responsible neural circuits, and the internal state of aged individuals. How age-dependent changes in internal states and neural circuits affect memory formation remains unclear. Here, we show in Drosophila melanogaster that aged flies of both sexes form robust appetitive memory conditioned with nutritious sugar, which suppresses their high mortality rates during starvation. In contrast, aging impairs the formation of appetitive memory conditioned with non-nutritious sugar that lacks survival benefits for the flies. We found that aging enhanced the preference for nutritious sugar over non-nutritious sugar correlated with an age-dependent increase in the expression of Drosophila neuropeptide F, an ortholog of mammalian neuropeptide Y. Furthermore, a subset of dopaminergic neurons that signal the sweet taste of sugar decreases its function with aging, while a subset of dopaminergic neurons that signal the nutritional value of sugar maintains its function with age. Our results suggest that aging impairs the ability to form memories without survival benefits; however, the ability to form memories with survival benefits is maintained through age-dependent changes in the neural circuits and neuropeptides.