The present invention provides methods of identifying and distinguishing different types of nerve cells in ex vivo cell culture, the method comprising the steps of: a) culturing somato-sensory nerve cells ex vivo, b) loading the nerve cells with a calcium, sodium, or voltage-sensitive indicator or expressing a genetically encoded calcium, sodium, or voltage-sensitive indicator, c) pulsing the nerve cells with an electrical train of bipolar square waves at two different voltages and two different frequencies； wherein the first voltage is 10 V/cm or less (low voltage) and the second voltage is between 12 and 20 V/cm (high voltage)； and wherein the first frequency is 5 Hz or less (low frequency) and the second frequency is between 15 and 20 Hz (high frequency), and d) detecting activation of the nerve cell by measuring the changes in the signal intensity of the indicator, wherein low voltage and low frequency activation indicates a first type of cell and activation detected only at high voltage indicates a second type of cell.
