Compute titration thresholds in current

[KK]

I'm running neuro titration simulations and want to output the titration thresholds in Amps. How do I compute this?

[LJ]

What I would do is get the current in the source EM simulation (check out how to do that here) and then multiply that by the titration factor.

[AntoninoMC]

@KK The titration procedure provides a scaling factor that must be applied to the stimulation source (incident E-field, input current, or voltage applied at electrode pairs) in order to initiate an action potential in a fiber or neuron.

Here are some examples depending on the stimulation source:

1. Source: Incident E-field (e.g., induced by TMS)
   Assume the incident electric field is 1 V/m, and the titration procedure yields a titration factor, tf.

   • The threshold E-field is therefore tf [V/m].
   • If this 1 V/m field results from a coil current rate of change dI/dt = A [A/s], then the threshold dI/dt required is A × tf [A/s].

2. Source: Applied voltage
   Let the applied voltage across an electrode pair be V = V₀. This value is also used as the Dirichlet boundary condition in low-frequency (LF) simulations.

   • If the titration factor is tf, the threshold voltage becomes V₀ × tf [V].

3. Source: Applied current
   Let the applied current to an electrode pair be I = I₀, typically derived from LF simulations via a current flux integrator.

   • With a titration factor tf, the threshold current is I₀ × tf [A].

The titration factor tf is a dimensionless number that gains physical meaning when applied to the relevant stimulation quantity (electric field, voltage, or current).

@LJ was suggesting the correct course of action. I hope this clarification is helpful!