A novel homeostatic plasticity model realized by random fluctuations in excitatory synapses

Homeostatic plasticity in mammalian central nervous system is considered to maintain activity in neuronal circuits within a functional range. In the absence of homeostatic plasticity neuronal activity is prone to be destabilized because correlation-based synaptic modification, Hebbian plasticity, induces positive feedback change. Several studies on homeostatic plasticity assumed the existence of a process for monitoring neuronal activity and adjusting synaptic efficacy on a time scale of hours, but its biological mechanism still remains unclear. Excitatory synaptic efficacy is associated with the size of a post-synaptic element, dendritic spine, and the size of the dendritic spine fluctuates even after neuronal activity is silenced. These fluctuations could be a non-Hebbian form of synaptic plasticity that serves such a homeostatic function. This study proposed and analyzed a synaptic plasticity model incorporating random fluctuations and Hebbian plasticity at excitatory synapses, and found that it prevents excessive changes in neuronal activity by adjusting synaptic efficacy. Random fluctuations do not monitor neuronal activity, but their relative influence depends on neuronal activity. The proposed synaptic plasticity model acts as a form of homeostatic plasticity, regardless of neuronal activity monitoring. Thus, random fluctuations play an important role in homeostatic plasticity and contribute to development and functions of neural networks.