Cooperation across timescales between and Hebbian and homeostatic plasticity

We review a body of theoretical and experimental research on the interactions of homeostatic and Hebbian plasticity, starting from a puzzling observation: While homeostasis of synapses found in experiments is slow, homeostasis of synapses in most mathematical models is rapid, or even instantaneous. Even worse, most existing plasticity models cannot maintain stability in simulated networks with the slow homeostatic plasticity reported in experiments. To solve this paradox, we suggest that there are both fast and slow forms of homeostatic plasticity with distinct functional roles. While fast homeostatic control mechanisms interacting with Hebbian plasticity render synaptic plasticity intrinsically stable, slower forms of homeostatic plasticity are important for fine-tuning neural circuits. Taken together we suggest that learning and memory relies on an intricate interplay of diverse plasticity mechanisms on different timescales which jointly ensure stability and plasticity of neural circuits.