Figure 8. Removal of extracellular Ca²⁺ blocks the activity-dependent enhancement of I_M together with the activity-dependent decline in synaptic gain.

A, replacement of extracellular Ca²⁺ with Mg²⁺ blocked changes in the I–V curves induced by stimulation with the 40 s synaptic template. Curves in black were recorded before stimulation and curves in grey after stimulation. B, similar results were seen in 6 of 6 B neurons where Ca²⁺ removal blocked the activity-dependent increase in I_M−30 (P= 0.0002). C, gain measurements from the same 6 neurons showing that Ca²⁺ also inhibited the decline in gain normally seen during virtual synaptic stimulation. Differences between the two curves are significant by the fourth 4 s repeat (P < 0.01).