SLOW POTENTIAL SHIFTS AT SLEEP-WAKE TRANSITIONS AND SHIFTS BETWEEN NREM AND REM-SLEEP

Scalp-recorded direct current (DC) potentials and their topographical distribution (F3, F4, C3, C4 and Pz) were investigated at the transiti on from wakefulness to sleep, and during NREM-REM sleep and REM-NREM s leep transitions in 11 healthy men during normal sleep. Changes in end expiratory CO2 partial pressure (ETCO(2)), scalp temperature and polys omnographic data were simultaneously measured. The transition to sleep was associated with a negative potential shift reaching significance bilaterally at frontal and central sites 5 to 10 minutes after sleep o nset (p < 0.05). Largest shifts were found at frontal locations 10 to 15 minutes after sleep onset averaging (mean +/- SEM) -512 +/- 103 mu V. Negative DC potential shifts also occurred at the transitions from NREM to REM sleep and from REM to NREM sleep, but were, however, less pronounced. The negative DC shift at NREM-REM sleep transitions preced ed the REM sleep onset (assessed conventionally by polysomnographic cr iteria) by about 1.5 minutes. Changes in temperature, ETCO(2) and eye movements were ruled out as factors significantly contributing to the generation of these shifts. Assuming a neuronal origin of the DC poten tial, the negative shifts at the wake-sleep transition and between NRE M and REM sleep suggest a temporary phase of increased cortical excita bility.