Assessment of nonlinear interactions in event-related potentials (ERPs) elicited by stimuli presented at short inter-stimulus intervals

The recording of brain event-related potentials (ERPs) is a widely used technique to investigate the neural basis of sensory perception and cognitive processing in humans.. However, when the temporal interval between two consecutive stimuli used to elicit ERPs is smaller than the latency of the main ERP peaks, i.e., when the stimuli are presented at a fast rate, overlaps between the ERPs elicited by successive stimuli may occur. These overlaps are usually dealt with by assuming that there is no nonlinear interaction between these responses, and thereby by performing algebraic waveform subtractions. Here we propose a straightforward approach to assess the presence of nonlinear interactions in a ERPs. This approach is a direct consequence of the concept of nonlinearity between two successive impulsive-like stimuli. By applying this approach to ERPs elicited by nociceptive cutaneous stimuli delivered at inter-stimulus intervals (ISIs) ranging from 250 ms to 2000 ms, we provide evidence that there are no nonlinear interactions between nociceptive ERPs, even at the shortest ISIs.