Too many cooks? Intrinsic and synaptic homeostatic mechanisms in cortical circuit refinement

Maintaining the proper balance between excitation and inhibition is critical for the normal function of cortical circuits. This balance is thought to be maintained by an array of homeostatic mechanisms that regulate neuronal and circuit excitability, including mechanisms that target excitatory and inhibitory synapses, and mechanisms that target intrinsic neuronal excitability. In this review, I discuss where and when these mechanisms are used in complex microcircuits, what is currently known about the signaling pathways that underlie them, and how these different ways of achieving network stability cooperate and/or compete. An important challenge for the field of homeostatic plasticity is to assemble our understanding of these individual mechanisms into a coherent view of how microcircuit stability is maintained during experience-dependent circuit refinement.