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LEMS extension: <WritableRequirement>

In the NeuroML formulation, a neuron may be influenced by external mechanisms (such as synapses and input sources) that inject it with current (or chemical substances, when using pure LEMS or EDEN’s Multiflux extension). The neuron receives inward flows as aggregates for each chemical species of interest, and its state is influenced by every aggregate.

However, there exist neuron models where a synapse may instantly and non-linearly alter a neuron’s internal state, in a way that changes the effect of other synapses (for example, fast saturation effects). EDEN allows such types of instant synpse-to-neuron effects through the <WritableRequirement> extension to LEMS <ComponentType> dynamics.

Note: At the moment, this feature is only supported for synapses attached to point neurons.

The <WritableRequirement> tag

<WritableRequirement> tags look much like <Requirement>s, with required name and dimension attributes. The difference is that they can also be assigned values from the mechanism requiring them — even though they exist in another!

Assigning a value to a <WritableRequirement> is done with a <StateAssignment>; where the variable name typically refers to a <StateVariable> of the same mechanism, a <WritableRequirement> of another mechanism’s quantity may be used instead.

Examples using <WritableRequirement> will be provided soon, stay tuned. Until then, see a usage example in EDEN’s program tests which shows how set a “trigger flag” of a cell from a synapse.