Past, present, and future of sleep medicine research in Latin America.

Sleep medicine is a relatively young field with exponential growth in development and research in the last decades. Parallel to the advances in the United States, Latin America also had its beginnings in sleep medicine housed in neuroscience laboratories. Since the very first Latin American meeting in 1985, and the first sleep society in 1993, sleep research has undergone significant development in subsequent years.

The Impact of Sound on Electroencephalographic Waves during Sleep in Patients Suffering from Tinnitus.

Based on the knowledge that sensory processing continues during sleep and that a relationship exists between sleep and learning, a new strategy for treatment of idiopathic subjective tinnitus, consisted of customized sound stimulation presented during sleep, was tested. It has been previously shown that this treatment induces a sustained decrease in tinnitus intensity; however, its effect on brain activity has not yet been studied. In this work, we compared the impact of sound stimulation in tinnitus patients in the different sleep stages.

Impact of reduction of tinnitus intensity on patients' quality of life.

Objective: Assess the impact of a reduction of tinnitus intensity achieved through sound stimulation during sleep on the improvement in the patients' quality of life.

Design: Acoustic stimuli consisted of a highly customized sound that reproduced the spectral and intensity characteristics of the tinnitus in each patient. This stimulus was uploaded into a portable electronic device and delivered through customized ear buds during sleep, every night for three months.

Auditory input modulates sleep: an intra-cochlear-implanted human model.

To properly demonstrate the effect of auditory input on sleep of intra-cochlear-implanted patients, the following approach was developed. Four implanted deaf patients were recorded during four nights: two nights with the implant OFF, with no auditory input, and two nights with the implant ON, that is, with normal auditory input, being only the common night sounds present, without any additional auditory stimuli delivered. The sleep patterns of another five deaf people were used as controls, exhibiting normal sleep organization.

Temporal correlation between auditory neurons and the hippocampal theta rhythm induced by novel stimulations in awake guinea pigs.

The hippocampal theta rhythm is associated with the processing of sensory systems such as touch, smell, vision and hearing, as well as with motor activity, the modulation of autonomic processes such as cardiac rhythm, and learning and memory processes. The discovery of temporal correlation (phase locking) between the theta rhythm and both visual and auditory neuronal activity has led us to postulate the participation of such rhythm in the temporal processing of sensory information. In addition, changes in attention can modify both the theta rhythm and the auditory and visual sensory activity.

Electroencephalographic frequencies associated with heart changes in RR interval variability during paradoxical sleep.

Brain stem autonomic oscillators, hypothalamic and cortico-frontal centre, entrained by baroreceptor input, have been proposed as the control system of the heart rhythm. Recent reported results in animals suggested that the hippocampal theta waves might also participate as a heart rate modulator. A temporal correlation among the firing of neurons in the medulla, the R-wave of the electrocardiogram, hippocampal units, and theta rhythm was reported in guinea pigs.

Novelty-induced correlation between visual neurons and the hippocampal theta rhythm in sleep and wakefulness.

Various rhythms have been shown to affect sensory processing such as the waking-sleep cycle and the hippocampal theta waves. Changes in the firing of visual lateral geniculate nucleus neurons have been reported to be dependent on the animal's behavioral state. The lateral geniculate extracellular neuronal firing and hippocampal field activity were recorded in chronically implanted animals to analyze the relationship during quiet wakefulness and sleep associated with stimulation shifts that may introduce novelty.

Cochlear microphonic changes after noise exposure and gentamicin administration during sleep and waking.

These experiments were designed to investigate the effect of noise, sleep, and gentamicin on the cochlear microphonic (CM) of the guinea pigs. Are the changes observed due to intrinsic cochlear phenomena or to efferent system actions? To answer this question, noise exposure together with efferent system blockade by gentamicin administration was performed. In the normal (non-treated) animal, noise exposure decreased both variability and amplitude of the tone evoked CM in about the first 10 min while the physiological modulation of slow wave sleep increasing the CM is not present.

Temporal correlations between heart rate, medullary units and hippocampal theta rhythm in anesthetized, sleeping and awake guinea pigs.

The aim of the present report was to determine whether or not the heart rate could show any relation to a central electrographic rhythm such as hippocampus theta. Our experimental design included anesthetized as well as chronically implanted guinea pigs. The cross-correlation, spike trigger averaging, between the medullary neurons firing, or the R-wave of the electrocardiogram, or hippocampal units, and theta rhythm revealed phase-locking during epochs of wakefulness, slow wave sleep and paradoxical sleep, and under anesthesia.

In vivo approach to the cellular mechanisms for sensory processing in sleep and wakefulness.

1. 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 phase locking of the response to the hippocampal theta rhythm, (b) changes in the discharge rate and firing pattern of the response to sound, and (c) changes in the effects of the neurotransmitters involved in the afferent and efferent pathways.

Effects of excitatory amino acid antagonists on the activity of inferior colliculus neurons during sleep and wakefulness.

The contribution of N-methyl-D-aspartate to the response to sound of guinea pig inferior colliculus neurons was analyzed by recording single-unit activity before and after iontophoretic injection of a receptor specific antagonist, 2-amino-5-phosphonovaleric acid (AP5), during the sleep-waking cycle. The AP5 produced a significant firing decrease in most of the units recorded, while some neurons exhibited a particular decrease in the later part of the response. A latency reduction in one out of three units in paradoxical sleep was observed.

Hippocampal theta rhythm synchronizes visual neurons in sleep and waking.

The hippocampal theta rhythm (theta) was reported to be associated with movements, attention, auditory processing, autonomic functions, learning and memory and postulated as an associator of discontiguous events. Since visual information includes temporal cues, our study was centered on the correlation between hippocampal theta rhythm and lateral geniculate activity. Phase relationships between hippocampal theta and unit firing were found with both spontaneous and light evoked activity during wakefulness, slow wave and paradoxical sleep.