[The auditory system in sleep]

The sensory information that the central nervous system receives represents an enormous amount of data coming from the outer world and from the body itself. This constitutes a set of influences that affects the general brain developing as well as on the sleep-waking organization.

We have proposed changes in the auditory information processing throughout the sleep-wakefulness cycle may be at least partially evidenced by single neurons extracellular recordings. We introduce the concept that the neural network organization during sleep vs that of wakefulness is different and can be modulated by sensory signals, and vice versa, the sensory input may be influenced by the central nervous system asleep or awake. During sleep the evoked firing of auditory units increases, decreases or remains similar to that observed during quiet wakefulness. There has been no auditory unit yet that stopped firing as the guinea pig enters sleep. Approximately half of the cortical neurons studied did not change firing rate when passing into sleep while others increased or decreased. Thus, the system is continuously aware of the environment.

We postulate that those neurons that changed their evoked firing during sleep, increasing or decreasing, are part of active sleep processes. Thus, the continuous sensory information input to the brain during sleep may serve to 'sculpt', modulate, the brain by activity-dependent mechanisms of neural development as has been postulated for wakefulness.