Evoked potential correlates of stable inter-individual differences in rat behaviour

Individual differences in rats' exploratory behaviour are stable over time, suggesting inherent differences in brain mechanisms for handling sensory information. These differences may have a neurophysiological basis since a negative correlation was found between individual variation in exploratory behaviour and recovery functions of cortical visual evoked potentials. Recovery functions were an expression of the extent to which the visual system recovered its responsiveness following initial stimulation. They were obtained by using pairs of flash stimuli separated by 3 interstimulus intervals (ISIs): 100, 200 and 300 msec. Recovery was defined as the amplitude of the response to the second flash expressed as a proportion of the response to the first flash. Only short latency components of the evoked responses were considered. The mean value for recovery averaged over the three ISIs constituted the recovery function. Only responses recorded when rats were quiet but alert were used for analysis. Evoked potential recovery functions appear to reflect a neurophysiological mechanism underlying the different capacities of individual rats for responding to novelty.