Neuroscience/Sleep
Massimini et al 2005 stimulated sleeping (NREM) volunteers with TMS whilst recording with EEG and found that the brain failed to communicate this injected current. Their conclusion is that cortical effective connectivity fails during sleep and that this could explain the loss of consciousness during sleep. Some theories of consciousness (e.g. Guilio Tononi, the head of Massimini's lab) postulate that communication between different regions of cortex might be one sign of consciousness.