Changes in reflex excitability of spinal motor neurons during day sleep in newborn infants.

A study was made of monosynaptic reflexes elicited by electrical stimulation of the ulnar and fibular nerves (H-reflexes) in newborn children, age five to seven days, during the sleeping--waking cycle. The amplitude of the H-responses was maximal and the coefficient of variation was minimal during the orthodox sleep state (OS) characterized by slow EEG waves and synchronous movement of the chest and stomach. During paradoxial sleep (PS), characterized by desynchronous EEG activity, rapid eye movements, and asynchronous breathing movements of the chest and stomach, the amplitude of the H-responses fell to 25 to 40% of the level during OS, and the coefficient of variation was in excess of 100%. The amplitude of H responses during the waking state was 60% that of the OS stage. The results of the study are considered from the point of view of existing theories about the reorganization of the system of controlling movements during the sleeping--waking cycle.