# Cortical Neurons Adjust the Action Potential Onset Features as a Function of Stimulus Type
## 3 Results
### AP Waveform Parameter Differences Due to Stimulus Type  
The calculated AP parameters (i.e., rapidity, threshold, amplitude, and width) for the somatosensory cortex RS and FS neurons were separately compared across the stimulation types (i.e., step-and-hold vs. frozen noise) to examine the effect of the stimulus type on the AP shape. The AP onset parameters were significantly different between the two stimulation types in RS pyramidal neurons. The Wilcoxon signed-rank test on the grand average of the rapidity of the AP revealed a significant increase in the rapidity of the AP for the RS neurons when the frozen noise was used as a stimulus compared to the conventional step-and-hold stimulation paradigm for both the IFWd\({}^{2}\) (\(Z=-3.92\), \(p<0.001\), with an effect size of r\({}^{2}\) = 0.38; see Figure 3) and the phase slope method (\(Z=-3.92\), \(p<0.001\), with an effect size of r\({}^{2}\) = 0.38; see Table 1). \begin{table}
\begin{tabular}{l c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c}{**Regular-Spiking Neurons**} & \multicolumn{2}{c}{**Fast-Spiking Neurons**} \\ \cline{2-5}  & **Step-and-Hold** & **Frozen Noise** & **Step-and-Hold** & **Frozen Noise** \\ \hline Rapidity (IFWd\({}^{2}\)) & \(3.97\pm 0.62\) & \(5.41\pm 0.19\) & \(6.40\pm 2.03\) & \(6.33\pm 1.76\) \\ Rapidity (Phase slope) & \(13.48\pm 3.89\) & \(24.24\pm 7.10\) & \(18.67\pm 4.81\) & \(25.54\pm 5.89\) \\ Threshold & \(-26.60\pm 4.30\) & \(-32.15\pm 8.05\) & \(-35.34\pm 4.29\) & \(-39.74\pm 4.78\) \\ Amplitude & \(81.12\pm 21.43\) & \(94.69\pm 18.16\) & \(74.88\pm 10.91\) & \(83.55\pm 10.88\) \\ Width & \(1.51\pm 0.36\) & \(1.35\pm 0.26\) & \(0.51\pm 0.09\) & \(0.49\pm 0.10\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: AP parameters (Mean \(\pm\)\(SD\)) of RS and FS neurons in response to the conventional step-and-hold current and synaptic-like current (frozen noise current). Figure 3: The effect of stimulation methods on the rapidity of action potential (mean \(\pm\)\(SD\)) for two types of somatosensory cortical neurons: RS and FS. An increase in AP rapidity was observed when frozen noise (FN) stimulation was used compared to the conventional step-and-hold current clamp stimulation method. No significant difference in the rapidity was observed for the FS neurons (Wilcoxon signed-rank test). Additionally, there was a significant increase in AP rapidity of FS neurons compared to RS neurons, regardless of the stimulation configuration (Mann–Whitney U test; * denotes \(p<0.05\) and ** denotes \(p<0.01\)). Conversely, FS neurons showed no significant differences in the resulting average rapidity of the elicited APs compared across stimulus types (frozen noise vs. step-and-hold; IFWd\({}^{2}\): \(Z=-0.34\), \(p=0.97\); see Figure 3). However, a significant increase in the AP phase slope-based rapidity for the frozen noise elicited responses compared to the step-and-hold current stimulation (\(Z=-3.92\), \(p<0.001\), with an effect size of r\({}^{2}=0.38\); see Table 1). Furthermore, RS and FS neurons both fired at different thresholds in response to the two stimulation protocols. A significant decrease in the average threshold potential was found when the frozen noise stimulation was used compared to the current step-and-hold stimulation for both RS (Wilcoxon signed-rank test: Z = \(-3.17\), \(p=0.002\), with an effect size of r\({}^{2}=0.25\)) and FS neurons (Wilcoxon signed-rank test: Z = \(-3.58\), \(p<0.001\), with an effect size of r\({}^{2}=0.32\)). Nevertheless, the threshold variation, a characteristic of somatic recording in central mammalian neurons, increased significantly for RS neurons but only slightly for FS neurons. The threshold variation, indicated by the threshold \(SD\), almost doubled when RS neurons were stimulated by synaptic-like current (4.3 mV variation with step-and-hold current and 8.05 mV variation with frozen noise current), while the threshold variation only increased by 11.4% in FS neurons (Table 1).