Dynamic properties of the responses to fast omitted stimulus potential paradigm in human.

Visual evoked potentials (VEPs) and omitted stimulus potentials (OSPs) were analyzed on scalp recordings of 10 healthy subjects. OSP responses, obtained after the due-time of the first omitted stimulus at the end of a conditioning stimulus train have been studied mostly in animals. Two types of visual OSP responses were observed in the previous studies: slow (< or = 2 Hz) and fast (> or = 5 Hz). In this study, some dynamic properties of the responses to high frequency flash stimulation were investigated. Very short conditioning trains and even only two stimuli were found to be sufficient for the generation of an OSP response. With longer conditioning periods, of ca. 250 ms the OSP response develops and reaches its final size and shape, similar to the results obtained from animal studies. In the topographical analysis, the steady state response (SSR) amplitudes were found to be larger in the occipital and parietal regions while the OSP responses spread homogeneously in all subjects.