P300 and sleep-related positive waveforms (P220, P450, and P900) have different determinants.

Stimulus factors known to influence the amplitude of the well known endogenous event-related potential (ERP) component P300 were manipulated to determine whether they have the same, or a different, influence on the amplitude of positivities of the sleep ERPs identified as P220, P450, and P900. Behavioral responsiveness and ERPs were recorded as subjects moved from wakefulness to sleep while performing an oddball task. The task consisted of sequential presentation of target and non-target tone stimuli with instructions to respond to targets with a finger--lift response. The probability of the target and non-target stimuli was varied (0.2/0.8, 0.5/.05 and 0.8/0.2) across three test conditions. While subjects were awake, P300 was maximal parietally with amplitude inversely related to the relative probability of the evoking stimulus and directly related to its task relevance. Positive waveforms (P220, P450, P900) recorded in sleep were largest at frontal and central recording sites. P220 and P900 amplitudes were inversely related to stimulus probability. P220 was smaller following target relative to non-target stimuli. Processes underlying P220, P450, and P900 sleep-related waveforms are different from those underlying the P300 component seen in alert wakefulness. The sleep positivities may be state-related waveforms subject to modulation by psychological processes.