 Thus, the brain will record fewer densely rich memories during these frequent periods of disengagement from the present moment.Consequently, the subjective perception is often that time passes by at a faster rate with age.Stimulants such as thyroxine, caffeine, and amphetamines lead to overestimation of time intervals by both humans and rats, while depressants and anesthetics such as barbiturates, nitrous oxide can have the opposite effect and lead to underestimation of time intervals.