COMMENT
Spike Timing Dependent Weight Adjuster
with symmetric functions (i.e. only depends on the absolute value of the
time difference, not on its sign.
Andrew Davison, UNIC, CNRS, September 2004
ENDCOMMENT
NEURON {
POINT_PROCESS StdwaSymm
RANGE interval, tlast_pre, tlast_post
RANGE deltaw, wmax, f
GLOBAL tau_a, tau_b, a, on
POINTER wsyn
}
ASSIGNED {
interval (ms) : since last spike of the other kind
tlast_pre (ms) : time of last presynaptic spike
tlast_post (ms) : time of last postsynaptic spike
f : weight change function
deltaw : change in weight
wsyn : weight of the synapse
tas (ms2) : tau_a squared
}
INITIAL {
interval = 0
tlast_pre = 0
tlast_post = 0
f = 0
deltaw = 0
}
PARAMETER {
tau_a = 20 (ms) : crossing point from LTP to LTD
tau_b = 15 (ms) : decay time constant for exponential part of f
wmax = 1 : min and max values of synaptic weight
a = 0.001 : step amplitude
on = 1 : allows learning to be turned on and off globally
}
NET_RECEIVE (w) {
tas = tau_a * tau_a : do it here in case tau_a has been changed since the last spike
if (w >= 0) { : this is a presynaptic spike
interval = tlast_post  t
tlast_pre = t
f = (1  interval*interval/tas) * exp(interval/tau_b)
deltaw = wmax * a * f
} else { : this is a postsynaptic spike
interval = t  tlast_pre
tlast_post = t
f = (1  interval*interval/tas) * exp(interval/tau_b)
deltaw = wmax * a* f
}
if (on) {
wsyn = wsyn + deltaw
if (wsyn > wmax) {
wsyn = wmax
}
if (wsyn < 0) {
wsyn = 0
}
}
}
