Local variable time step method (Lytton, Hines 2005)

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Accession:33975
The local variable time-step method utilizes separate variable step integrators for individual neurons in the network. It is most suitable for medium size networks in which average synaptic input intervals to a single cell are much greater than a fixed step dt.
Reference:
1 . Lytton WW, Hines ML (2005) Independent variable time-step integration of individual neurons for network simulations. Neural Comput 17:903-21 [PubMed]
Model Information (Click on a link to find other models with that property)
Model Type:
Brain Region(s)/Organism:
Cell Type(s):
Channel(s):
Gap Junctions:
Receptor(s):
Gene(s):
Transmitter(s):
Simulation Environment: NEURON;
Model Concept(s): Methods;
Implementer(s): Hines, Michael [Michael.Hines at Yale.edu];
: $Id: netcon.inc,v 1.1.1.1 2003/09/02 19:05:02 hines Exp $

COMMENT
USAGE: for most receptors
*****************************************************************************
    NEURON {
      POINT_PROCESS NAME
    }

    PARAMETER {
      Cdur	= 1.08	(ms)		: transmitter duration (rising phase)
      Alpha	= 1	(/ms mM)	: forward (binding) rate
      Beta	= 0.02	(/ms)		: backward (unbinding) rate
      Erev	= -80	(mV)		: reversal potential
    }
    
    INCLUDE "netsyn.inc"
*****************************************************************************

USAGE: for NMDA receptor
*****************************************************************************
    NEURON{ POINT_PROCESS NMDA
      RANGE B 
    }

    PARAMETER {
      mg        = 1.    (mM)     : external magnesium concentration
      Cdur	= 1.	(ms)	 : transmitter duration (rising phase)
      Alpha	= 4.	(/ms mM) : forward (binding) rate
      Beta	= 0.0067 (/ms)	 : backward (unbinding) rate 1/150
      Erev	= 0.	(mV)	 : reversal potential
    }

    ASSIGNED { B }

    INCLUDE "netcon.inc"
    : EXTRA BREAKPOINT MUST BE BELOW THE INCLUDE
    BREAKPOINT {
      rates(v)
      g = g * B : but don't really need to readjust conductance
      i = i * B : i = g*(v - Erev)
    }

    PROCEDURE rates(v(mV)) {
      TABLE B
      DEPEND mg
      FROM -100 TO 80 WITH 180
      B = 1 / (1 + Exp1(0.062 (/mV) * -v) * (mg / 3.57 (mM)))
    }
*****************************************************************************
ENDCOMMENT

INDEPENDENT {t FROM 0 TO 1 WITH 1 (ms)}

NEURON {
  RANGE g
  NONSPECIFIC_CURRENT i
  GLOBAL Cdur, Alpha, Beta, Erev, Rinf, Rtau
}

UNITS {
  (nA) = (nanoamp)
  (mV) = (millivolt)
  (umho) = (micromho)
  (mM) = (milli/liter)
}

ASSIGNED {
  v		(mV)		: postsynaptic voltage
  i 		(nA)		: current = g*(v - Erev)
  g 		(umho)		: conductance
  Rinf				: steady state channels open
  Rtau		(ms)		: time constant of channel binding
  R				: fraction of open channels
  synon
}

STATE {Ron Roff}

INITIAL {
  R = 0
  Rinf = Alpha / (Alpha + Beta)
  Rtau = 1 / (Alpha + Beta)
  synon = 0
}

BREAKPOINT {
  SOLVE release METHOD cnexp
  g = (Ron + Roff)*1(umho)
  i = g*(v - Erev)
}

DERIVATIVE release {
  Ron' = (synon*Rinf - Ron)/Rtau
  Roff' = -Beta*Roff
}

: following supports both saturation from single input and
: summation from multiple inputs
: if spike occurs during CDur then new off time is t + CDur
: ie. transmitter concatenates but does not summate
: Note: automatic initialization of all reference args to 0 except first

NET_RECEIVE(weight, on, nspike, r0, t0 (ms)) {
  : flag is an implicit argument of NET_RECEIVE and  normally 0
  if (t>0) { : bug fix so that init doesn't send a false event
    if (flag == 0) { : a spike, so turn on if not already in a Cdur pulse
      nspike = nspike + 1
      if (!on) {
        r0 = r0*Exp1(-Beta*(t - t0))
        t0 = t
        on = 1
        synon = synon + weight
        state_discontinuity(Ron, Ron + r0)
        state_discontinuity(Roff, Roff - r0)
      }
      : come again in Cdur with flag = current value of nspike
      net_send(Cdur, nspike)
    }
    if (flag == nspike) { : if this associated with last spike then turn off
      r0 = weight*Rinf + (r0 - weight*Rinf)*Exp1(-(t - t0)/Rtau)
      t0 = t
      synon = synon - weight
      state_discontinuity(Ron, Ron - r0)
      state_discontinuity(Roff, Roff + r0)
      on = 0
    }
  }
}

FUNCTION Exp1(x) {   
  if (x < -100) {
    Exp1  = 0
  } else if (x > 100) {
    Exp1 = exp(100)
  } else{
    Exp1 = exp(x)
  }
}

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