Thalamic deactivation at sleep onset precedes that of the cerebral cortex in humans.
Proceedings of the National Academy of Sciences of the United States of America February 23, 2010 Michel Magnin, Marc Rey, Hélène Bastuji et al.
Thalamic deactivation at sleep onset typically precedes cortical deactivation by several minutes, while reactivation during awakening is synchronized. Delays vary between subjects for similar cortical regions, and cortical activity heterogeneity during sleep onset is greater than previously thought. Asynchronous thalamo-cortical deactivation may explain hypnagogic hallucinations and the common overestimation of time needed to fall asleep.