Long-term information storage by the interaction of synaptic and structural plasticity

The continuous turnover of synapses observed in cortical networks poses a severe problem for storing long-term memory in the connectivity of these networks. Yet, in this chapter, we demonstrate that this can be resolved by considering connections consisting of multiple synapses.We show that, under certain conditions, the interaction of synaptic and structural plasticity induces a collective dynamics across all synapses between two neurons with stable states at zero and at multiple synapses. This dynamics leads to experimentally observed connectivity and enables long-term information storage despite synaptic turnover.Furthermore, the resulting connectivity can be controlled by external stimulations: very low or high stimulation levels quickly drive the neurons to become connected with zero or multiple synapses, respectively. Using this to actively store information on multisynaptic connections entails that information storage can be orders of magnitude faster than information retention under intermediate stimulation levels