Fig. 6. The different thresholds for action potential generation. (A) Middle trace: intracellular recordings of the responses to just threshold, afferent nerve (Aff) and parallel fibers (PF) stimulation at resting membrane potential. Lower trace: the two responses were superimposed on voltage hyperpolarization evoked by 1 nA negative current injection. Upper trace: the response to supra-threshold positive injection of 1 nA current. (B) The area marked in A (broken line) is displayed at higher gain in B. Arrows point toward the different thresholds (note the sharp transient deflections on the onset and offset of the current pulse, reflecting bridge balancing artifacts).