Analysis of the fluctuations in the interspike intervals of abducens nucleus neurons during ocular fixation in the alert cat.

The behavior of abducens nucleus motoneurons and internuclear neurons was recorded during eye fixation in the alert cat. The interspike interval (ISI) values during a given fixation followed a normal distribution, with coefficients of variation for motoneurons and interneurons ranging from 4.6 to 16% and 5.7 to 21.7%, respectively. The ISI mean was linearly related to its standard deviation and to the coefficient of variation. The power spectral density of ISI fluctuations did not reveal any relevant peak. The autocorrelation function of ISI fluctuations was flat except at the origin. Results suggest the presence of a gaussian white noise superimposed on the clock-like firing of the activity of abducens neurons during ocular fixation. Some physiological implications of the results are discussed.