How did Ivan Pavlov explain the effect of sleep on nervous inhibition?

The Russian physiologist Ivan Pavlov proposed that sleep is the result of the irradiation of inhibition among cortical and subcortical neurons—the nerve cells located in the outer layer of the brain and the layers beneath the cortex.1

In his work on the laws of the conditioned reflex, Pavlov viewed sleep as a process involving the spread of this inhibition throughout the nervous system. He considered this inhibitory state to be a protective mechanism, particularly in the context of his later research on psychoses, where he suggested that excessive inhibition serves to shut out the external world and exclude injurious stimuli that might otherwise cause extreme excitation.2