How is point process current added into the equation solved by NEURON

[gabrielggn]

Dear colleagues,

I today started asking myself this simple question "How is point process current added into the equation solved by NEURON".
Indeed, from what I understood from the NEURON book, the membrane potential equation solved is typically solved with current density (through distributed mechanisms). However as pointed out in other post, Point Process are distributed at one point (-> 0 surface then).

I was then wondering how is this current incorporated into the membrane potential equation (is the current divided by the area of the segment ?) .

I was specifically asking myself this question in the case of synapses/synaptic current, as one could consider the case of a point synapses (~Point process), what represents the weight typically used to couple the synapses between cells. Indeed, the conductance of the synapse (post-synaptic conductance) isn't supposed to represent everything in the strength of the connection at this single synapse ? ( so weight would represent Nb synapses/Nb of AMPA ion channels at the synapse and proba of the glutamate binding ?)

Hope everything is fine in US, especially with administration constraints on scientific funding.
Best,
Gabriel

[ted]

The ODE for each segment is of the form
transmembrane capacitive current + transmembrane ionic current = sum of all currents arriving in the segment from adjacent segments + sum of all currents that enter the segment from all point processes that generate currents

Notice that current in these equations is in absolute units, not density units.

For some, but not all, synaptic mechanisms, the first element of the weight vector is used to specify the peak conductance elicited by a unitary synaptic activation. Examples include ExpSyn and Exp2Syn. For others it is not used at all.

Governmental interference has been going on for a long time, and not just in the US, but it isn't the only problem facing research funding. Excessive indirect cost charges constitute a long-standing and ever-increasing drag in the US. Why should it cost taxpayers almost $2 to provide $1 of support to research? Indirect costs used to be exorbitant only at "premier" research institutions ("we're worth it, just see how many Nobel prizes we have won"); sadly this is no longer the case, and merit can no longer be cited as the excuse. That's one reason why PIs have to write so many proposals to get one award.

[gabrielggn]

Dear Ted,

Thank you very much for this answer. If I understand properly, all current densities are scaled with segments' dimensions (surface of the segment) and then are incorporated each PP currents.

Indeed, sorry for the stupid question, in the doc it's well written:

Code: Select all

G_syn = weight * factor * (exp(-t/tau2) - exp(-t/tau1))

Then the weight is just what is often called the g_bar or maximal conductance of the synapse. I was mainly confused when looking at NetPyNe code using weights for synaptic mechanism without the mention of weight in their .mod files (but I guess it's a generic call for weight and g).

Indeed it is a sad time for public research. Hope the best for what's comes next even if it's going on the wrong direction so far.