The pattern of activity generated by thalamocortical systems changes dramatically during different states of the nervous system, such as sleep,waking, and epileptic seizures. The presence of these changes in thalamocortical activity have been known for more than 100 years, owing to the pioneering work of an Englishman named Richard Caton (1887).
Part of Dr. Caton's Abstract: Researches on Electrical Phenomena of Cerebral Gray Matter. Transactions of the Ninth International Medical Congress (1887) 3: 246-249.
"On applying one electrode to the external surface of the brain, and the other to the surface of a vertical section, vigorous currents passed through the galvnometer. Further fluctuations of the current were observed sometimes, coinciding with some movement of the animal's body or some change in its mental condition. In deep anaesthsia, for example, considerable deflection of needle was generally observed, lessening gradually as the animal regained consciousness. And when death was caused by prolonged anaesthesia...considerable deflection occurred and shortly after death the needle fell to zero."
These state dependent changes in the activity of thalamocortical systems are well illustrated in the activity of the electroencephalogram, or EEG.