A power toothbrush includes a handle portion having a drive system therein for moving a set of bristles with a frequency and amplitude to produce clinically effective cleaning results. A modulation system modulates the drive signal by changing the frequency or duty cycle of the drive signal with a frequency varying modulation signal. The modulation frequency will increase from the start to the conclusion of a brushing event for cognitive stimulation while the modulation frequency will decrease between the start and conclusion of a brushing event for cognitive relaxation.