  A new stimulation paradigm is presented for the stimulation of nerve cells by
extracellular electric currents. In the new paradigm stimulation is achieved
with the current spike induced by a voltage step whenever the voltage step is
applied to a live biological tissue. By experimental evidence and theoretical
arguments, it is shown that this spike is well suited for the stimulation of
nerve cells. Stimulation of the human tongue is used for proof of principle.
Charge injection thresholds are measured for various voltages. The time-profile
of the current spike used in the experiment has a half-width of about 1
microsecond. The decay of the spike is non-exponential. The spike has at least
three distinctly different phases. A Maxwell phase is followed by a
charge-rearrangement phase. Charging of cell membranes is completed in a third
phase. All three phases contribute to depolarization or hyperpolarization of
cell membranes. Due to the short duration of the spike the charge transfer is
very small. The activation time (time of no return) of nerve cell membranes
leading to an action potential is measured and found to be unexpectedly short.
It can become as short as 3 microseconds for a voltage step of 10 V or higher.
