Experimental design. Bottom, In each experimental block participants received a stream of ∼3,138 somatosensory stimuli (blue), consisting in brief electrical pulses delivered transcutaneously at 9.5 Hz to the left median nerve at the wrist. Throughout the somatosensory stimulation, 40 loud and fast-rising auditory stimuli (red) were delivered every 6–10 s through a loudspeaker placed in front of the participant's left hand. Top left, Each auditory stimulus elicited a large-amplitude VP in the ongoing 64-channel EEG, consisting in a centrally distributed negative–positive deflection maximal at the vertex (Cz, highlighted in white in the scalpmaps). Top right, Electrical stimuli elicited early SEPs consisting of three main peaks (N20, P25, and P45) maximal over the somatosensory cortex contralateral to the stimulated hand (electrodes highlighted in white in the scalpmaps). Note the smaller amplitude and higher frequency of SEPs compared with the VP. In subsequent analyses we assessed whether the amplitude of early SEPs depended on where they occurred with respect to the phase of the concomitant VP.