Cerebral Modulation of Circadian Sleep-Wake Rhythms

An fMRI Study of the Effects of Vibroacoustic Stimulation on Functional Connectivity in Patients with Insomnia

BACKGROUND

It is well known that vibratory and auditory stimuli from vehicles such as cars and trains can help induce sleep. More recent literature suggests that specific types of vibratory and acoustic stimulation might help promote sleep, but this has not been tested with neuroimaging. Thus, the purpose of this study was to observe the effects of vibroacoustic stimulation (providing both vibratory and auditory stimuli) on functional connectivity changes in the brain using resting state functional magnetic resonance imaging (rs-fMRI), and compare these changes to improvements in sleep in patients with insomnia.

METHODS

For this study, 30 patients with insomnia were randomly assigned to receive one month of a vibroacoustic stimulation or be placed in a waitlist control. Patients were evaluated pre- and postprogram with qualitative sleep questionnaires and measurement of sleep duration with an actigraphy watch. In addition, patients underwent rs-fMRI to assess functional connectivity.

RESULTS

The results demonstrated that those patients receiving the vibroacoustic stimulation had significant improvements in measured sleep minutes as well as in scores on the Insomnia Severity Index questionnaire. In addition, significant changes were noted in functional connectivity in association with the vermis, cerebellar hemispheres, thalamus, sensorimotor area, nucleus accumbens, and prefrontal cortex.

CONCLUSIONS

The results of this study show that vibroacoustic stimulation alters the brain's functional connectivity as well as improves sleep in patients with insomnia.

The Hyperpolarization-Activated HCN4 Channel is Important for Proper Maintenance of Oscillatory Activity in the Thalamocortical System

Hyperpolarization-activated cation channels are involved, among other functions, in learning and memory, control of synaptic transmission and epileptogenesis. The importance of the HCN1 and HCN2 isoforms for brain function has been demonstrated, while the role of HCN4, the third major neuronal HCN subunit, is not known. Here we show that HCN4 is essential for oscillatory activity in the thalamocortical (TC) network. HCN4 is selectively expressed in various thalamic nuclei, excluding the thalamic reticular nucleus. HCN4-deficient TC neurons revealed a massive reduction of Ih and strongly reduced intrinsic burst firing, whereas the current was normal in cortical pyramidal neurons. In addition, evoked bursting in a thalamic slice preparation was strongly reduced in the mutant mice probes. HCN4-deficiency also significantly slowed down thalamic and cortical oscillations during active wakefulness. Taken together, these results establish that thalamic HCN4 channels are essential for the production of rhythmic intrathalamic oscillations and determine regular TC oscillatory activity during alert states.

Neurophysiology of circadian rhythm sleep disorders of children with neurodevelopmental disabilities

This article reviews circadian rhythm sleep disorders (CRSDs) of children with neurodevelopmental disabilities. These sleep disturbances frequently occur in this population but they are misunderstood and under diagnosed. The causes and features of CRSD in children with brain disorders differ in many ways from those seen in typically developing children. It is the brain, including the eyes, which regulates sleep and circadian rhythmicity by modulating pineal melatonin production/secretion and when there is significant brain damage, the sleep/wake patterns may be modified. In most instances CRSD are not disorders of the suprachiasmatic nuclei because these small hypothalamic structures only adjust their functions to the changing photic and non-photic modulatory influences. Each form of CRSD is accompanied by characteristic changes in serum melatonin levels and clinical features. When nocturnal melatonin production/secretion is inappropriately timed or impaired in relation to the environment, timed melatonin replacement therapy will often be beneficial. In this review an attempt is made to clarify the neurophysiological mechanisms underlying the various forms of CRSD because without understanding the photic and non-photic influences on sleep, these sleep disorders can not be fully characterized, defined or even appropriately treated. In the future, the existing definitions for the different forms of CRSD should be modified by experts in pediatric sleep medicine in order to include children with neurodevelopmental disabilities.

Melatonin has membrane receptor-independent hypnotic action on neurons: an hypothesis

Melatonin, which is known to have sleep-promoting properties, has no morpho-physiological barriers and readily enters neurons and their subcellular compartments from both the blood and cerebrospinal fluid. It has multiple receptor-dependent and receptor-independent functions. Sleep is a neuronal function, and it can no longer be postulated that one or more anatomical structures fully control sleep. Neurons require sleep for metabolically driven restorative purposes, and as a result, the process of sleep is modulated by peripheral and central mechanisms. This is an important finding because it suggests that melatonin should have intracellular sleep-inducing properties. Based on recent evidence, it is proposed that melatonin induces sleep at the neuronal level independently of its membrane receptors. Thus, the hypnotic action of melatonin and the mechanisms involving the circadian rhythms are separate neurological functions. This is contrary to the presently accepted view.