The 2015 ION Mini-Symposium on Systems Neuroscience was held at the Institute of Neuroscience on July 4th, 2015. Profs. Jose Carmena (University of California, Berkeley, USA), Vikaas Sohal (University of California, San Francisco, USA), Nirao Shah University of California, San Francisco, USA ), Botond Roska (University of Basel, Switzerland) presented their recent findings. Prof. Muming Poo hosted this symposium. More than 160 researchers from ION attended this symposium.