Figure 2.

Detection and classification of somatic or axon initial segment generated APs. A, Somatic (Som.; red) or AIS (blue) generated APs were determined by calculating the second derivative of each AP. As shown by previous studies (Meeks and Mennerick, 2007), the second derivative of the voltage traces of somatically generated APs exhibit a biphasic waveform during the rising phase, whereas AIS-generated APs exhibit a pronounced biphasic dip (arrow). B, The site of AP generation transitioned from the soma to AIS during current ramps, most likely due to the large somatic voltage change caused by the current ramp injection protocol, and was consistent and reproducible over multiple ramps (C). The color scale indicates the number of APs in 100 ms bins.