Synaptic noise and other sources of randomness in motoneuron interspike intervals.

Publisher Website
Google Scholar
Abstract
Intra-cellular recordings from cat spinal motoneurons were used to investigate sources of variability in the interval between action potentials during repetitive firing. These records reveal a sequence of spike, repolarization, and linearly rising depolarization, followed by another spike when the firing level is crossed. Since the membrane potential fluctuated even in the resting state, such "synaptic noise" superimposed upon the otherwise linear depolarization might be expected to cause variations in the time when the firing level is reached. This model is tested by measuring the firing level and depolarization rate from a motoneuron, setting up a real-time working model on a computer, and adding synaptic noise from the same motoneuron to the artificial depolarization sequence. Times at which the artificial firing level is crossed are compiled into a histogram which is then compared to that motoneuron''s interspike interval histogram. Synaptic noise is often sufficient to account for the interval variability, both when the firing level is constant and when it is observed to increase with time following the preceding spike.