Statistical approach to inter-spike interval ramps

This study presents a statistical analysis of single unit neural activity in the dorsal anterior cingulate cortex (dACC) in awake macaque monkeys. Based on spiking activity, a series of inter-spike intervals (ISI) are obtained. ISI series carries information on neural activities and instantaneous firing frequency. These series are analyzed using an explicit, finite Markov chain with memory. Model states represent the length of ISI ramp. The statistics of increasing and decreasing ISI ramps are observed separately. This paper analyzes the probability density function (pdf) and the model parameters obtained from original ISI series: the stationary state probabilities, the transition probabilities and normalized histogram of Markov chain per 1000 samples. As a control parameter, for each one of ISI time series 40 surrogate signals were generated. We have obtained the presentation of neural activity over the states as a function of time and typical shapes of the pdf for increasing and decreasing branch of the model.