Performance of spontaneously hypertensive rats in a peak-interval procedure with gaps.

The purpose of the present experiment was to evaluate timing behavior in spontaneously hypertensive rats (SHR), and compare it to the performance of Wistar Kyoto (WKY), and Wistar (WI) rats. In the first phase of the experiment, the subjects were exposed to a peak-interval procedure, in which fixed-interval 30s trials were alternated with nonreinforced and extended (peak) trials. After 60 sessions, an approximation to a Gaussian probability density function was fitted to the response rate during peak trials in order to estimate the peak time, the peak rate and the Weber fraction. The results showed no difference among the strains in the peak time and the Weber fraction, but a higher peak rate in SHR. In the second phase of the experiment, a gap procedure was introduced; in 80% of the peak trials the stimuli associated with the fixed interval and peak trials were turned off for 9s. Gap trials produced peak time shifts that were longer than those expected if the clock had stopped during the gap but shorter than those had the clock been reset, and no significant differences between the strains were found. Given the great importance that different theories give to temporal processing in the development of the main symptoms of attention deficit hyperactivity disorder (ADHD), and the existence of time perception deficits in humans with ADHD, the present results question the validity of SHR as an animal model of that disorder, and suggest the necessity of exploring the timing behavior of other animal models of ADHD.