Correlation between steady potential baseline and event-related slow potential magnitude in the rat

Event-related slow potential (SP) responses to a warning stimulus were recorded from rat frontal and visual cortex during performance of a reaction-time task. Measurements of steady potential baseline and magnitude of the negative SP response were obtained for individual trials (presented at variable intervals). The correlation between baseline and SP response magnitude was examined utilizing both amplitude and integrated area data. Also, averaged SP responses were obtained by selecting trials for averaging according to baseline potential. Slow potential response magnitude was inversely correlated with baseline negativity. Neither baseline nor SP response amplitude was correlated with trial number of intertrial interval. Averaged SP responses consisting of trials with more positive baselines were larger in magnitude than averaged SP responses consisting of trials with more negative baselines. The steady potential level attained during trials with more positive baselines was not more negative than the level reached during trials with negative baselines. These data are consistent with the concept of "ceiling" effect for event-related slow potentials.