Suppression of the auditory middle-latency response and evoked gamma-band response in a paired-click paradigm.

When two clicks are presented within 500 ms and the clicks are separated by several seconds, a typical finding is a suppression of the amplitude of the P50 component of the middle-latency auditory-evoked response. In the present study, we investigated whether only the P50 or also the earlier components Po, Na, Pa and Nb, and the exogenous components N100 and P200 exhibit an amplitude suppression to the second click. In addition, we studied the suppression behaviour of the auditory-evoked 40-Hz gamma-band response in the time and frequency domain. We found a significant amplitude suppression to the second click for all components of the auditory-evoked potential following Po, which was most pronounced at electrode Cz. When testing the successive peaks and troughs of the evoked 40-Hz gamma-band response in the time domain, we found a significant amplitude suppression for peaks and troughs with the same latency and polarity as the middle-latency components following Po, which was most pronounced at electrodes Fz and Cz. Consequently, the amplitude of the 40-Hz evoked gamma-band response in the frequency domain paralleled the findings of the time domain, with a significant amplitude suppression to the second tone, which was most pronounced at electrodes Fz and Cz. Results are discussed with reference to the early sensory-gating hypothesis.