  A simple threshold model of neuron firing (with the neuron membrane
electrochemical potential governed by the chaotic Rossler attractor) has been
analyzed by mapping the generated irregular spiking time-series into telegraph
signals. In this model the fundamental frequency of the chaotic Rossler
attractor provides (with a period doubling) the strong periodic component of
the generated irregular signal. The exponentially decaying broad-band part of
the spectrum of the Rossler attractor has been transformed by the threshold
firing mechanism into a scaling tale. These results are compared with irregular
spiking time-series obtained in vitro from a spontaneous activity of
hippocampal (CA3) singular neurons (rat's brain slice culture). The comparison
shows good agreement between the model and experimentally obtained spectra.
