Figure 5. Macroscopic Ca²⁺ thresholds for the occurrences of synaptic modifications.

(A,B) An inverse BCM rule (A) and a sigmoid function (B) described the correlation between the macroscopic synaptic modifications and the magnitudes of Ca²⁺ pulses according to the range of Ca²⁺ amplitudes analysed. The term EC₅₀ stands for the [Ca²⁺] required to achieve half-maximum LTD. (C) Simulations performed with higher [CaN] (the control concentration of CaN and other components of the model are indicated in (A)). (D,E) A reduction of [PP1] (D) had little effect on the overall behaviour of the model, but an increase (E) in its concentration changed θ_m. (F) Reduction of [αCaMKII] altered the value of θ_m of the inverse BMC rule. In (C–F) the light gray line corresponds to the results obtained with the control model (A) replotted for comparison. (G) An increase of [αCaMKII] or a reduction of [CaN] or [PP2A] suppressed the occurrence of LTP (the control result (B) was replotted in gray for comparison). (H) The elevation of [PP2A] or the absence of αCaMKII resulted in the suppression of LTD. Each dot in the panels is the mean + SEM calculated for 100 simulations. The duration of the Ca²⁺ pulses was 20 s for all simulations.