A novel hypothesis to explain the effect of inter-stimulus interval (ISI) on the amplitude of the N1 and P2 waves.

The effect of ISI on the amplitude of the auditory and somatosensory N1 and P2 could be explained by the modulation of a single neural component whose time course overlaps the peak latency of the N1 and P2 waves (middle column). This component could appear in the EEG either (A) as a negative deflection that is enhanced at very short ISIs, or (B) as a positive deflection that is reduced at very short ISIs. In both cases, at very short ISIs the magnitude of the N1 would be increased and the magnitude of the P2 would be decreased (right column). Note that in this model, the neural components underlying the N1 and P2 waves per se are not modulated by ISI (left column).