Figure 7.

Memory retention problem and timescales. (A) Illustration of metaplastic thresholds stabilizing the learning. Synapses are stable at in the ongoing regime, then a “plasticity trace” builds up during presentation of new sensory inputs, but this will eventually be stopped by a sliding activation threshold, allowing the synapse to adapt to those novel stimuli. (B) Illustration of the multiple timescales involved in plasticity, from the membrane time constant τ_m to the homeostatic one τ_homeo, ranging from ms to days.