A comparison of the repetitive click and conditioning-testing P50 paradigms.

The auditory P50 ERP component has previously been studied either in the repetitive click or the conditioning-testing (C-T) paradigm. For 20 subjects, we compared 4 repetitive click and 4 C-T protocols in a single experimental session with identical recording techniques and with interclick intervals comparable to the C-T intervals. In the C-T protocols, a long interval between click pairs ensured full recovery of P50 to the C click. The analysis of P50 topographies provided strong evidence that the same component was measured in the two paradigms. For both paradigms, P50 amplitude was progressively suppressed as the interclick or C-T interval decreased (P < 0.0001), with parallel interval vs. P50 amplitude regression lines for the two paradigms. There was a strong trend (P = 0.08) for the repetitive click amplitudes to be smaller than T amplitudes for comparable repetitive click and C-T intervals. Equivalently, this strong trend suggests that repetitive click intervals must be longer (by about 300 ms) than the C-T interval to generate equivalent amplitude P50 responses. We conclude that the same component is measured in both paradigms, that P50 amplitude decreases with decreasing interstimulus intervals in both paradigms, and that in normals, for comparable inter-click and C-T intervals, there is greater P50 suppression in the repetitive click paradigm. Finally, we note that the comparison of paradigms within normals does not necessarily apply to clinical samples.