a specific threshold tracking technique is "threshold electrotonus", which uses the threshold tracking set-up to produce long-lasting subthreshold depolarizing or hyperpolarizing currents within a membrane. changes in cell excitability can be observed and recorded by creating these long-lasting currents. threshold decrease is evident during extensive depolarization, and threshold increase is evident with extensive hyperpolarization. with hyperpolarization, there is an increase in the resistance of the internodal membrane due to closure of potassium channels, and the resulting plot "fans out". depolarization produces has the opposite effect, activating potassium channels, producing a plot that "fans in".