Observing the Current Input in Neurons

We propose a new technique that uses an observer to determine the current input into a neuron whose voltage is measured electrophysiologically. The current observer efficiently inverts the conductance-based model equations of the cell for the input, and also obtains the dynamics of the gating variables as a by-product. We show a version of the algorithm that is suitable for practical implementation. Theoretically, we prove the global convergence of the observer for all models of the Hodgkin-Huxley formalism. The current observer is accurate and can be implemented either offline or concurrently with the recording. It can potentially be useful even to in vivo recordings. We illustrate the workings of the observer on several neuronal models.