[Does neuroscience understand dreaming?]

Sleep is a succession of two stages: slow-wave and rapid eye-movement sleep. The later has mixed characteristics between sleep and wakefulness. Therefore, dreams have been proposed to occur during this stage. This hypothesis is now considered as oversimplified. Dreaming may occur during the two stages though with different characteristics. Deciphering brain structures associated with dreaming is difficult. However, during the two stages, a decrease in low-frequency and an increase in high-frequency electrical activity in posterior cortical regions has been reported that might be the neural correlate of dreaming. The origin of cortex stimulation is under debate, but the mechanisms involved are similar to those acting during wakefulness. Dream function is not known and it might be an epiphenomenon originating from synaptic transmission noise. Depriving subjects of rapid-eye movement sleep for two weeks has no apparent effect on their behavior.