The well-known extreme variability of spinal cord reflex output has defied analysis suing classical statistics. This variability renders the interpretation of electrophysiologic monitoring during spasticity surgery extremely difficult. Preliminary studies have re-evaluated reflex output data using new techniques developed for the analysis of complex phenomena. In the normal human, it appears that reflexes fluctuate on many different time scales: seconds, minutes, and perhaps hours. Physical systems which fluctuate on many time scales are """"""""self-similar"""""""", and this is the hallmark of a """"""""fractal"""""""" process. The results generate the following working hypothesis: time-series of spinal cord reflex output fluctuate with a fractal pattern. this idea will be rigorously tested using data collected from the spinal cord of the decerebrate cat including: 1) neuronal population response, 2) individual neuron firing frequency and 3) the tendon force generated. Data will be obtained while varying the frequency of stimulation and with the reflex feedback loop opened and closed. to characterize fractal behavior, non-linear analytical methods will be extensively used. By employing simulated data sets as mathematical controls, these methods should help determine whether the observed fractal patterns originate from deterministic or stochastic processes. The results of this work are important from both clinical and basic science perspectives. Clinically, proving that spinal cord reflexes fluctuate on time scales far longer than the measuring period permitted in the operating room would lead to a radical shortening of operative time and risk. On a basic level, the results will provide information leading to a deeper understanding of the origin of apparently random fluctuations in a simple input-output neural circuit in the mammalian nervous system. It is expected that the results of this study will be applicable to more complex neural circuits in the central nervous system.
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