F Examples of electrophysiological properties of humanneurons: control individual (top); PKAN patient (bottom). Traces on the left represent trains of action potentials induced by injection of a suprathreshold current step through the patch electrode in current-clamp mode. Middle traces show Na+ and K+ currents (down- and upward-deflecting from baseline, respectively) in response to a 60 mV step from a holding voltage of -70 mV in voltage-clamp mode. Insets on the right display enlarged portions of the traces to magnify fast Na+ currents. G Histogram with percentages of recorded cells showing repetitively firing (z-test). 