Infection and inflammation are frequently associated with impairment in learning and memory, but the mechanistic basis of this effect is unclear. In Nature Medicine, Yang and colleagues use systemic exposure of mice to the synthetic RNA duplex poly(I:C) to simulate a viral infection and assess its effect on learning tasks. Poly(I:C) substantially impairs learning in a manner dependent on the cytokine TNF. Bone-marrow chimeras or selective-depletion approaches show that monocytes and macrophages present outside the central nervous system, not microglia that reside in the central nervous system, are the key source of the TNF responsible for impairing learning. At the cellular level, learning is known to be influenced by spine remodeling on neuronal dendrites. In a reporter mouse in which they can track changes in spine remodeling, the authors observe greater alterations after exposure to poly(I:C).

Nat. Med. (15 May 2017) doi:10.1038/nm.4340