Increased variability in motor output with brain-spinal cord interaction.

Spinal cord neural circuitry of the lamprey that forms a central pattern generator for locomotion interacts with reticular neurons forming a reticulo-spino-reticular loop. We examine the hypothesis that increased variability exists in the locomotor output in the presence of this loop. Fictive locomotion (rhythmic activity recorded from ventral roots (VR)) was induced in in-vitro brain-spinal cord preparations of adult lampreys, by bathing the spinal cord with excitatory amino acids. In the control conditions the brain was bathed with physiological saline. Subsequently, synaptic reticular neuron communication was suppressed by application of a zero Ca2+ saline or, the brain was detached. The mean value of the predominant period was given by the lag to the first peak in the autocorrelation of the full wave rectified, moving averaged VR activity (zero mean, normalized). Variability in signal amplitude and burst duration or cycle period is indicated by attenuation of the peak values at lags > zero and the rate of decay of the autocorrelation. Also, power spectral density calculations were used to determine the dominant frequencies. Increased variability is indicated by wider peaks and higher power in a broader frequency band. Each index indicated the presence of increased variability when the reticular-spinal loop was functional.