Natural sleep modifies the rat electroretinogram

We show here electroretinograms (ERGs) recorded from freely moving rats during sleep and wakefulness. Bilateral ERGs were evoked by flashes delivered through a light-emitting diode implanted under the skin above one eye and recorded through electrodes inside each orbit near the optic nerve. Additional electrodes over each visual cortex monitored the brain waves and collected flash-evoked cortical potentials to compare with the ERGs. Connections to the stimulating and recording instruments through a plug on the head made data collection possible at any time without physically disturbing the animal. The three major findings are (i) the ERG amplitude during slow-wave sleep can be 2 or more times that of the waking response; (ii) the ERG patterns in slow-wave and REM sleep are different; and (iii) the sleep-related ERG changes closely mimic those taking place at the same time in the responses evoked from the visual cortex. We conclude that the mechanisms that alter the visual cortical-evoked responses during sleep operate also and similarly at the retinal level.