Modular arrangement of synaptic and intrinsic homeostatic plasticity within visual cortical circuits

Neocortical circuits use synaptic and intrinsic forms of homeostatic plasticity to stabilize key features of network activity, but whether these different homeostatic mechanisms act redundantly or can be independently recruited to stabilize different network features is unknown. Here, we used pharmacological and genetic perturbations both in vitro and in vivo to determine whether synaptic scaling and intrinsic homeostatic plasticity (IHP) are arranged and recruited in a hierarchical or modular manner within layer 2/3 (L2/3) pyramidal neurons in the rodent primary visual cortex (V1). Surprisingly, although the expression of synaptic scaling and IHP was dependent on overlapping signaling pathways, they could be independently recruited by manipulating spiking activity or NMDA receptor (NMDAR) signaling, respectively. Further, we found that changes in visual experience that affect NMDAR activation but not mean firing selectively trigger IHP, without recruiting synaptic scaling. These findings support a modular model in which synaptic and IHP respond to and stabilize distinct aspects of network activity.