The effects of sleep stages and time of night on NREM sleep ERPs.

Event-related potential (ERP) is one of the best techniques for studying information processing during sleep because it does not require behavioral responses or consciousness awareness. Several ERP components have been identified during non-rapid eye movement (NREM) sleep, but the associated underlying processes of these waveforms remain unclear. The present study examines the effect of sleep stage and time of night on the NREM ERPs to further understand these processes. An oddball paradigm was conducted in 11 healthy subjects to elicit ERPs throughout the night. Polysomnographic recordings were also applied to identify sleep stages. The results showed that P220, N350, and P900 decreased during the second half of the night, when the NREM sleep drive is partially satiated. This finding is consistent with the notion that the NREM ERPs reflect an inhibitory process associated with sleep drive. P220 and P900 were also found to increase as subjects entering deep sleep. However, the N350 was not affected by the deepening of sleep and peaked earlier during stage 1 sleep. Although these components are all related to the process for sleep preservation, the N350 may be more associated with sleep-wake transition and the P220 and P900 with the process of deepening of sleep.