Neural integrators and working memory rely on persistent activity, a widespread neural phenomenon potentially involving persistent sodium conductances. Using a unique combination of voltage-clamp, dynamic-clamp and frequency-domain techniques, we have investigated the role of voltage-dependent conductances on the dendritic electrotonic structure of neurons of the prepositus hypoglossi nucleus (PHN), which is known to be involved in the oculomotor integration. The PHN contains two main neuronal populations: type B neurons with a double after hyperpolarization and type D neurons which not only are oscillatory but also have a greater electrotonic length than type B neurons. The persistent sodium conductance is present in all PHN neurons, however its effect on the dynamical electrotonic structure is shown to significantly differ in the two major cell types present in the nucleus. The electrotonic differences are such that the persistent sodium conductance can be almost perfectly manipulated in a type B neuron using an online dynamic-clamp to add or substract virtual sodium ion channels. The dynamic-clamp results are confirmed by data-fitted models which suggest that the persistent sodium conductance has two different roles depending on its somatic versus dendritic location: perisomatic conductances could play a major role in maintaining action potential discharge and dendritic conductances would be more involved in other computational properties, such as those involving remote synaptic processing or bi-stable events.