Sleep hippocampal theta rhythm and sensory processing

Abstract

Ancient human cultures have developed diverse forms of a device that, based on sensory stimulation, is used to put babies to sleep: the rocking cradle. Vestibular and somatosensory stimulation produced by the rocking movements, complemented by eye closure and other stimulation such as constant temperature and the mothers voice/song (lullaby) activating the auditory system, are able to induce sleep. On the other hand, it is a common experience that reducing the sensory afferent volleys to the brain can facilitate sleep. A series of experimental data will be presented demonstrating the sensory input relevance in the organization of the sleep and wakefulness cycle. Firing rate shifts in auditory and visual neurones, changes in the pattern of discharge, and, most important, the temporal correlation of the spike timing with the hippocampal theta rhythm, will be set forth. Sleep, a huge change in the brain physiology, depends on both, a series of active processes and passive mechanisms, e.g., functional sensory deafferentation3,19 and neural networks changing organization. Although many signs of active processes have been shown, there are not enough experimental data to support a final decision about the relative contribution of passive processes. 16,27,43,46 However, both approaches may be partially reconciled conceding that the deafferentation may be provoked by an inhibitory influence acting, e.g., upon the ascending activating reticular system. Our main purpose is to provide an experimental aspect of sensory data analysis, its relation to sleep and the hippocampal theta rhythm as an internal zeitgeher (time giver) for auditory and visual information processing.