We studied the electrical activity of the brain on timing behavior in rats. This study was investigated for the function of the brain on the temporal discrimination task in rats. In this experimental study, animals were trained in operant chambers using the peak-interval (PI) 30-s procedure that included fixed interval (FI) 30-s trials and probe trials. The FI 30-s trials consisted of a food pellet reinforcement that presented by the first lever press response more than 30-s after the onset of tone stimulus, and the stimulus was terminated. The probe trials delivered no reinforcement with responses and tone stimulus lasted for 90-s. The 3-s bin of lever press responses on probe trials showed a clear peak point. This PI procedure is a useful procedure to investigate about timing in rats.
The peak time corresponded to near the 30-s with reinforcement time. In the self-start group, the number of responses at the beginning of the trials exceeded that of the control group. But the peak point was the same as the autonomic start control group. The peak time corresponded to near the 30-s with reinforcement durations. The graph had a peak point that showed the peak of the regression curve fitting with the Poisson function. Then the electrodes were implanted in the rat brain. We measured the hippocampal electroencephalography (EEG) with performing PI procedure in rats. The electrodes were implanted in the sub-cortex brain areas. The EEG power of the hippocampus and striatum region showed hippocampal theta rhythm correlation with timing behavior patterns. These results suggest that the hippocampus and striatum oscillations are important with timing mechanism in the brain. The hippocampus and striatum may play a very important role to estimate the passage of the time in living animals.