Circadian and Ultradian Rhythms Modulating the Sensory Processing

The present review analyzes sensory processing during sleep and wakefulness from a single neuronal viewpoint. Our premises are that processing changes throughout the sleep– wakefulness cycle may be at least partially evidenced in single neurons by (a) changes in the discharge rate and firing pattern of the response to sound, (b) changes in the phase locking of the response to the hippocampal theta rhythm, and (c) changes in the effects of the neurotransmitters involved in the afferent and efferent pathways. 1. The concept that the neural network organization during sleep versus wakefulness is different and can be modulated by sensory signals and vice versa, and that the sensory input may be influenced by the CNS state, i.e., asleep or awake, is introduced. During sleep the evoked firing of auditory units increases, decreases, or remains similar to that