Respiratory-related evoked potentials during the transition from alpha to theta EEG activity in Stage 1 NREM sleep

It has been argued previously that evoked potential components during Stage 1 sleep in response to both auditory and respiratory stimuli are intermedi ate between those of wakefulness and Stage 2 sleep. However, state fluctuat ions in the EEG between alpha and theta during Stage 1 sleep have been link ed to changes in a number of respiratory functions including ventilation, u pper airway resistance and chemical drive. It was therefore hypothesized th at if respiratory related evoked potentials (RREP) were averaged separately for alpha and theta EEG periods during Stage 1 sleep, the alpha RREP would resemble wakefulness and the theta RREP would resemble Stage 2 sleep. RREP s were produced by 250 ms occlusions in 10 subjects. EEG was recorded from 29 scalp sites, referenced to linked ears, together with EOG and EMG. The N 1 component was not specifically associated with alpha vs. theta activity, but appeared to be sensitive to any decrease in arousal level, suggesting t hat it was more related to attention than to changes in the EEG. The late N 2 and P300 components were present during wake and Stage 1 alpha. However, in Stage 1 theta, different late components emerged (N300 and P450) that di ffered in latency, amplitude or topographical distribution from those seen in wakefulness. The P2 proved difficult to interpret, whereas the N550 did not appear until Stage 2 sleep. and as such, was not dependent on alpha/the ta state. The results indicate that RREP components are differentially affe cted by the transition into sleep.