COMMENT Author: Mark Cembrowski, 2012 This is an extension of the Exp2Syn class to incorporate NMDA-like properties, and incorporates some NMDA features from Elena Saftenku, 2001. First, Exp2Syn is described: 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. Next, two extensions have been included: 1. Ca tracking, mimicking Ca influx through NMDA channels NOTE: 060517: MSC: this is now removed in our simple model because no other calcium handling mechanisms are present, and this feature is unnecessary. 2. Voltage gating, mimicking Mg block ENDCOMMENT NEURON { POINT_PROCESS Exp2SynNMDA RANGE tau1, tau2, e, i, mgBlock NONSPECIFIC_CURRENT i RANGE g } UNITS { (nA) = (nanoamp) (mV) = (millivolt) (uS) = (microsiemens) } PARAMETER { tau1=.1 (ms) <1e-9,1e9> : the actual tau's for use are in init.hoc (CL) tau2 = 10 (ms) <1e-9,1e9> e=0 (mV) alpha_vspom = -0.062 (/mV) :-0.075: -0.0602: -0.08: -0.062 :voltage-dependence of Mg2+ block from Maex and De Schutter 1998 : -0.0602 from Spruston et al. (1995) (Ching-Lung) v0_block = 10 (mV): 0 extMgConc = 1 (mM) : external Mg concentration } ASSIGNED { v (mV) i (nA) g (uS) factor mgBlock :extMgConc (mM) } 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 } BREAKPOINT { SOLVE state METHOD cnexp g = B - A mgBlock = vspom(v) i = g*mgBlock*(v - e) } DERIVATIVE state { A' = -A/tau1 B' = -B/tau2 } NET_RECEIVE(weight (uS)) { A = A + weight*factor B = B + weight*factor } FUNCTION vspom (v(mV))( ){ vspom=1./(1.+0.2801*extMgConc*exp(alpha_vspom*(v-v0_block))) :voltage-dependence of Mg2+ block from Maex and De Schutter 1998 }