Figure 4. Effect of sudden change of the pool size $p$ on synaptic efficacies.

(A) After 2 min, the pool size is either doubled (solid curves) or set to zero (dotted curves). In response, the synaptic efficacies are scaled multiplicatively as receptors are redistributed through the system. Doubling the receptor pool has a relatively weak effect in this example, as the system starts with a high filling fraction of 0.9, meaning that 90% of the slots are already filled at the beginning and there are few empty slots to which the additional receptors can bind. (B) Same as A. but showing relative change in synaptic efficacies, which is identical for all synapses. (C) Change in pool size. After the sudden increase or decrease in pool size at 2 min, there is first a rapid relaxation of the pool size followed by a much slower return towards the original value. (D) Same as B. but for a filling fraction of $1/2$. The smaller filling fraction leads to bigger relative changes of the synaptic efficacies. Parameters used were: $\beta =1/43{\text{s}}^{-1}$, $\delta =1/14{\text{min}}^{-1}$. The desired relative pool size was set to $\varphi =2.67$. The production rate $\gamma$ and attachment rate $\alpha$ were calculated according to Equation 12 and Equation 13, respectively.