Positive extracellular waveform. A, The extracellular positive waveform (black) is identified by its large initial peak (return current or current source), a large trough (depolarization), and then sometimes followed by a second peak (posthyperpolarization peak). B, Positive waveforms are typically recorded distally from the AIS, near the dendrites and axon (pink). C, Schematic of current sources and sinks on the positive waveform. The process is similar to the triphasic waveform (Fig. 3C), but the recording electrode is more distal. D, Several subtypes of positive waveforms have been reported. Biphasic-positive waveforms are the most commonly reported positive waveforms, followed by positive-multiphasic or M-shaped, and finally, rarer HAPS. E, Schematic of positive and triphasic waveforms reflecting fibers of passage activity. As action potentials propagate along the afferent axon originating from distal brain areas (purple), a positive or triphasic waveform can be detected from the electrode (pink) in the recorded brain area (red).