COMMENT Two state kinetic scheme synapse described by rise time tau1, and decay time constant tau2. The normalized peak condunductance is 1. Decay time MUST be greater than rise time. The solution of A->G->bath with rate constants 1/tau1 and 1/tau2 is A = a*exp(-t/tau1) and G = a*tau2/(tau2-tau1)*(-exp(-t/tau1) + exp(-t/tau2)) where tau1 < tau2 If tau2-tau1 -> 0 then we have a alphasynapse. and if tau1 -> 0 then we have just single exponential decay. The factor is evaluated in the initial block such that an event of weight 1 generates a peak conductance of 1. Because the solution is a sum of exponentials, the coupled equations can be solved as a pair of independent equations by the more efficient cnexp method. ENDCOMMENT NEURON { POINT_PROCESS Exp2EPSG_NMDA RANGE tau1, tau2, e, gmax, Kd, gamma, mg, M, i NONSPECIFIC_CURRENT i RANGE g } UNITS { (nA) = (nanoamp) (mV) = (millivolt) (uS) = (microsiemens) } PARAMETER { tau1 = .1 (ms) <1e-9,1e9> tau2 = 10 (ms) <1e-9,1e9> Kd = 9.98 (mM) : modulate Mg concentration dependence gamma = 0.101 (/mV) : modulate slope of Mg sensitivity mg = 1.0 (mM) : extracellular Mg concentration e = 0 (mV) : reversal potential gmax = 1 (1) : peak conductance } ASSIGNED { v (mV) i (nA) g (uS) M : fraction of channels not blocked by extracellular Mg factor } STATE { A (uS) B (uS) } INITIAL { LOCAL tp if (tau1/tau2 > .9999) { tau1 = .9999*tau2 } A = 0 B = 0 tp = (tau1*tau2)/(tau2 - tau1) * log(tau2/tau1) factor = -exp(-tp/tau1) + exp(-tp/tau2) factor = 1/factor mgblock(v) } BREAKPOINT { SOLVE state METHOD cnexp mgblock(v) g = B - A i = g*gmax*M*(v - e) } DERIVATIVE state { A' = -A/tau1 B' = -B/tau2 } NET_RECEIVE(weight (uS)) { A = A + weight*factor B = B + weight*factor } PROCEDURE mgblock(v(mV)) { : from Jahr & Stevens M = 1. / (1. + exp(gamma * (-v)) * (mg / Kd)) }