Figure 6. Model of homosynaptic LTP accompanied by heterosynaptic LTD.

After 2 min, LTP is induced in synapses 2 and 3. This entails a transient synapse-specific change in the insertion rate $\alpha$ of these synapses and a gradual change in their slot numbers. (A) Time course of relative change of receptor insertion rate $\alpha$ and slot numbers of stimulated synapses undergoing homosynaptic LTP. (B) Time course of synaptic efficacies for a filling fraction of $F=0.9$ and a relative pool size of ${\displaystyle \varphi =2.67}$. Only a very small amount of heterosynaptic LTD can be observed in unstimulated synapses 1 and 4. (C) Relative change of synaptic efficacies and pool size due to homosynaptic LTP and heterosynaptic LTD in B as a function of time. (D) Same as C but for a smaller filling fraction of $F=0.5$ and a smaller relative pool size of $\varphi =1.0$. Note the smaller transient increase in efficacy of potentiated synapses (compare peaks of green curves in C and D) and the increased amount of heterosynaptic LTD (compare troughs of blue curves). (E, F) Maximum amount of homosynaptic LTP (E) and heterosynaptic LTD (F) as a function of relative pool size $\varphi$ for three different filling fractions.