Figure 1.

Electrophysiological definition of rat sleep states. Typical EEG samples taken from a rat W, in SWS, and during REM (left), and the EEG power spectra of such samples (right). During online averaging, flashes were delivered manually only when the EEG pattern was seen to be consistent with one of these three brain states. In experiments where single responses were collected, the moment of stimulus delivery was marked on the EEG record, and each response was later classified as W, SWS, or REM when the EEG trace was examined.