I've been playing around with MacGregor's point neuron model for a
couple of weeks now (I previously posted looking for anyone who might be
able to help me with parameter selection) and recently discovered a reason for
my problems: there's a typo.
Chapter 14, p. 239: the formula for potassium conductance says that
the increase with spiking is controlled by the time constant TGK. This is
wrong. The increase in potassium conductance should be instantaneous, as
illustrated in MacGregor and Oliver's 1974 paper in Kybernetik and in p.223 of
"Neural and Brain Modeling", Fig. 223.
It took me a while to catch this because MacGregor's source code for
the neuron model ("Neural and Brain Modeling", Appendix 2) incorporates the
same error. I've tried it both ways, and the 1974 formula is the one that
works.
By posting this, I hope to be able to save whoever else may be working
with the MacGregor model a lot of headache. I realize that there may be a lot
of subscribers to this newsgroup who knew this already, and to those people I
offer my apologies for wasting bandwidth.
In the helpful spirit in which this post was written, I would like to
offer as freeware a Mac application for single-neuron modeling. It uses a
(corrected) MacGregor point neuron model, and plots current-rate curves. It's
got all the bells and whistles I could think of on it, and I'll have some
documentation written on it by the end of next week. For those of you who
wrote me about it earlier, I still have your email and will be sending you
copies. All others, please email me.
___
Mitchell Maltenfort Northwestern Unversity Chicago, Illinois
Internet: mgm at nwu.edu Bitnet:mitchm at nuacvm.acns.nwu.edu
