(A) The inter–spike –trajectory of three sample neurons in mean–driven (left), intermediate (middle) and fluctuation–driven spiking regime (right). In the mean–driven regime the inter–spike trajectory moves directly from AHP resetting towards threshold, whereas in the fluctuation–driven regime the trajectory is convoluted and indirect (right). (B) The degree of convolution in the trajectory can be quantified using return mapping , i.e. plotting versus , and quantifying the fraction of points above versus below the unity-line (), which we refer to as the return map ratio . An even ratio close to 0.5 represents convoluted path (right), whereas a uneven ratio (close to 1) represent a direct path (left). Ratios are indicated in%. (C) The distribution of return map ratios for all ISIs, shown for two sample neurons, one having distribution mean close to 0.5, i.e. a fluctuation–driven regime and one having the mean close to 0.8, i.e. in the mean–driven regime (blue and green arrows). The mean return map ratio of all neurons () has a significant anti–correlation with skewness of firing rate distribution (D), spike irregularity () (E), as well as the least time spent below threshold (LTBT) of (F).