voltage instabilities when combining multiple voltageClampTriple elements

[JustasB]

I have a vclamp protocol that has more than three steps (to test channel inactivation and deactivation eg. p52 of ICG paper). When I chain two voltageClampTriple elements with non-overlapping durations, I get voltage and current instabilities at step transitions.

    <voltageClampTriple id="Input_1"
        active = "1"
        delay="50ms" duration="200ms"
        conditioningVoltage="-84mV"
        testingVoltage="50mV"
        returnVoltage="-30mV"
        simpleSeriesResistance="1e6ohm"/>
        
    <voltageClampTriple id="Input_2"
        active = "1"
        delay="300ms" duration="100ms"
        conditioningVoltage="-30mV"
        testingVoltage="-84mV"
        returnVoltage="-84mV"
        simpleSeriesResistance="1e6ohm"/>

Results in:

It seems that this could be avoided if the voltageClampTriple specified the duration of the final step, and the element logic only applied non-zero current during times inside the vclamp's time window.

This is the only place I could find the LEMS definition of the voltageClampTriple component. Is this the right place? I could add the bounds check to fix the problem. https://github.com/openworm/hodgkin_huxley_tutorial/blob/3915d4e393f520ce2f5dba6585357b439146cb38/Tutorial2/NeuroML2/vclamp.xml

CC @scrook

[pgleeson]

The voltageClampTriple is included in the latest version of the development branches and released in the latest beta release https://github.com/NeuroML/jNeuroML/releases. See https://github.com/NeuroML/NeuroML2/blob/development/NeuroML2CoreTypes/Inputs.xml#L632.

You can't really add 2 vclamps to one cell, as each of them will try to force the cell to one of its chosen voltage levels at any given time. It would be better t create a new <voltageClampMultiple> ComponentType which can have many (nonoverlapiing) child levels, and each one only applies a current during its part.

<voltageClampMultiple >
    <voltageLevel start=0ms stop=100ms voltage=10mV simpleSeriesResistance=1e6ohm>
    <voltageLevel start=100ms stop=300ms voltage=20mV simpleSeriesResistance=1e6ohm>
</voltageClampMultiple >

This would also let you make more complex protocols, e.g. with ramping sections, as voltageClampMultiple doesn't really care what it's children are doing, only that they produce a current. In fact the <compoundInput> element might do this already for you, but you probably need a new <voltageLevel> CT.

[JustasB]

I ended up adapting the voltageClampTripple code for my custom component with more steps (see below). I don't know LEMS well enough to express it in a more generic way that doesn't involve repetitious code.

    <ComponentType name="voltageClampProtocol" extends="baseVoltageDepPointCurrent">
        
        <Parameter name="active" dimension="none" />
        
        <Parameter name="delay" dimension="time" />
        <Parameter name="duration1" dimension="time" />
        <Parameter name="duration2" dimension="time" />
        <Parameter name="restingVoltage" dimension="voltage" />
        <Parameter name="voltage1" dimension="voltage" />
        <Parameter name="voltage2" dimension="voltage" />
        
        <Parameter name="simpleSeriesResistance" dimension="resistance"/>
        
        <!--TODO: remove! Only required as EventConnection is used in explicitInput to
         connect inputs to cells. Events aren't passed! ... -->
        <EventPort name="in" direction="in" description="Note this is not used here. Will be removed in future"/>
        
        <Dynamics>
            
            <StateVariable name="i" exposure="i" dimension="current"/>
            
            <OnEvent port="in"><!--TODO: remove, see above...
                                <StateAssignment variable="i" value="0"/>-->
            </OnEvent>
            
            <OnCondition test="active .eq. 1 .and. t .lt. delay">
                <StateAssignment variable="i" value="(restingVoltage - v) / simpleSeriesResistance"/>
            </OnCondition>
            
            <OnCondition test="active .eq. 1 .and. t .geq. delay .and. t .lt. (delay + duration1)">
                <StateAssignment variable="i" value="(voltage1 - v) / simpleSeriesResistance"/>
            </OnCondition>
            
            <OnCondition test="active .eq. 1 .and. t .geq. delay + duration1 .and. t .lt. delay + duration1 + duration2">
                <StateAssignment variable="i" value="(voltage2 - v) / simpleSeriesResistance"/>
            </OnCondition>
            
            <OnCondition test="active .eq. 1 .and. t .geq. delay + duration1 + duration2">
                <StateAssignment variable="i" value="(restingVoltage - v) / simpleSeriesResistance"/>
            </OnCondition>
            
        </Dynamics>
        
    </ComponentType>