Neuroscientists have often described the adult brain in similar terms to an electronic circuit board – dependent on fixed, precise connectivity. However, with the advent of technologies allowing chronic measurements of neural structure and function, the emerging picture is that neural networks undergo significant remodeling over multiple timescales, even in the absence of explicit learning or sensory perturbation. In my talk, I will present recent chronic imaging data on the long-term dynamics of synaptic networks and functional cell assemblies in the mouse auditory cortex and discuss concepts how to build stable sensory representations from unstable building blocks.