Event-related potentials in humans as indices of access to stored information during sleep.

The even-related potentials are good indices of brain functions during sleep stages. The contingent negative variation (CNV), occurring in the interval between a conditional and a target stimulus, reflects information processing. The emitted potential which occurs when an expected stimulus is omitted reflects the access to a specific memory. During waking, deep slow wave sleep (stage 4) and paradoxical sleep seven subjects were submitted to a CNV paradigm, the target stimulus of which was occasionally omitted. The endogenous components of the evoked potentials induced at Fz, Cz and Pz locations by the auditory stimuli were analysed during the three behavioral stages. During stage 4 they were of largest amplitude and longest latency. These results are discussed in terms of neural excitability. CNV and emitted potentials were observed during waking and paradoxical sleep, but not during stage 4. These results suggest that information processing occurs during paradoxical sleep with access to waking memories during this stage of sleep, whereas information processing is absent during stage 4.