Figure 3. Wide dynamic range aVLSI microchip emulation of NMDA receptor-mediated calcium dynamics.

(A) Top: the NMDA-dependent calcium circuit. The NMDA conductance g_NMDA (red) is scaled to generate calcium conductance g_Ca. This signal is sent to a WR-TCA to generate $I_{\mathrm{Ca}}^{+2}$. $I_{\mathrm{Ca}}^{+2}$ is sent to a current-voltage converter circuit to generate [Ca⁺²]. Bottom: the I_IN-V_OUT steady-state V-I curve of the current-voltage converter circuit. (B) Top: I_NMDA (red) and I_Ca (green) responses to a presynaptic AP at V_MEM=−40 and 0 mV, showing the NMDA channel voltage dependence and the presence of $I_{\mathrm{Ca}}^{+2}$ while I_NMDA≈0. Bottom: I_NMDA-V_MEM curve of the NMDA circuit in the presence (○) or absence (●) of [Mg⁺²] block. (C) Top: biological recording of [Ca⁺²] integration in response to a single or a pair of presynaptic pulses [adapted by permission from MacMillan Publishers Ltd.: Nature (Mainen 1999), copyright 1999]. Bottom: the circuit response to the same stimulation protocol (time scale apply to both top and bottom.)