The ability to discriminate successive signals separated by time intervals in the millisecond-range is an important element in analyzing the temporal characteristics of sensory input. When two identical stimuli are presented with a sufficient time interval between them, they are readily perceived as being two separate events. As they are presented progressively closer together, there comes a point when the two separate stimuli are perceived as one. However, the neural mechanism of temporal discrimination is unclear. Therefore, our major objective is to analyze, in detail, the effect of cortical excitability and inhibition on temporal sensory discrimination in healthy subjects.