The Journal of Neurophysiology Vol. 81 No. 6 June 1999, pp. 2823-2832
Copyright ©1999 by the American Physiological Society

Testing the Classification of Static  Axons Using Different Patterns of Random Stimulation

Laboratoire de Physiologie de la Perception et de l'Action. Collège de France, 75005 Paris, France

Petit, Julien, Robert W. Banks, and Yves Laporte. Testing the Classification of Static  Axons Using Different Patterns of Random Stimulation. J. Neurophysiol. 81: 2823-2832, 1999.Testing the classification of static  axons using different patterns of random stimulation. The possibility of using randomly generated stimulus intervals (with a Poisson distribution) to identify the type(s) of intrafusal fiber activated by the stimulation of single static  axons was tested in Peroneus tertius muscle spindles of anesthetized cats. Three patterns of random stimulation with different values of mean intervals [20 ± 4.47, 30 ± 8.94, and 40 ± 8.94 (SD) ms] were used. Single static  axons activating, in single spindles, either the bag₂ fiber alone or the chain fibers alone or both types of intrafusal fiber were prepared. Responses of spindle primary endings elicited by the stimulation of  axons were recorded from Ia fibers in cut dorsal root filaments. Cross-correlograms between stimuli and spikes of the primary ending responses, autocorrelograms, interval histograms of responses, and stimulations were built. The characteristics of cross-correlograms were found to be related not only to the type of intrafusal muscle fibers activated but also to the parameters of the stimulation. Moreover some cross-correlograms with similar characteristics were produced by the activation of different intrafusal muscle fibers. It also was observed that, whatever the type of intrafusal muscle fiber activated, cross-correlograms could exhibit oscillations after an initial peak, provided the extent in frequency of the primary ending response was small; these oscillations arise in part from the autocorrelation of the primary ending responses. Therefore, cross-correlograms obtained during random stimulation of static  axons cannot be used for unequivocally identifying the type(s) of intrafusal muscle fiber these axons supply.