“…Here, the drift current represents the “inner drive” leading to an elementary action (wrist motion), while the noise accounts for natural fluctuations, mainly due to the variable internal and external conditions. Since the original models using reflective boundary conditions 31 , 43 at the starting (“zero-current”) level were not able to reproduce the statistical properties of the measured actigraphy signals, we released the lower-bound conditions and allowed negative values for the driving current, as well, which may correspond to a sort of inhibition, similar to the hyperpolarization in nerve cells, in a lower level of hierarchy. Figure 5 B demonstrates the model-generated time series of spikes, while the results of a PDF analysis of the simulated signals, carried out as described under section 1 for the real HPA recordings, are shown in Fig.…”