Reduced brain GABA in primary insomnia: preliminary data from 4T proton magnetic resonance spectroscopy (1H-MRS)

Abnormal recovery function of somatosensory evoked potentials in patients with primary insomnia

Neurobiological correlates underlying insomnia are poorly understood. The hyperarousal of the central nervous system indicates that cortical excitability may be abnormal in patients with insomnia. The purpose of the present study was to investigate changes in cortical excitability by examining the recovery function of median nerve somatosensory evoked potentials (SEPs) in patients with primary insomia (PI). We studied the recovery function of median nerve SEPs in 12 medication-naive PI patients and in 12 age- and sex-matched healthy subjects. SEPs in response to single stimulus and paired stimuli at interstimulus intervals (ISIs) of 20, 60, 100 and 150 ms were recorded. The recovery function of the cortical components of frontal P20 and parietal N20 showed significantly reduced suppression in PI patients as compared to healthy controls. In conclusion, this is the first study investigating changes in cortical excitability in PI patients by examining the recovery function of median nerve SEPs. The present study suggests that cortical excitability is increased in PI patients. Dysfunction of inhibitory GABAergic interneurons of the cerebral cortex might contribute to the increased cortical excitability in PI patients.

Cortical GABA levels in primary insomnia

STUDY OBJECTIVES

GABA is increasingly recognized as an important neurotransmitter for the initiation and maintenance of sleep. We sought to measure cortical GABA content through proton magnetic resonance spectroscopy (MRS) in persons with and without primary insomnia, and relate brain GABA levels to polysomnographic sleep measures.

DESIGN

Two-group comparison study.

SETTING

Outpatient study at a university research clinic.

PARTICIPANTS

Non-medicated persons with primary insomnia (N = 16) and no sleep complaints (N = 17).

INTERVENTIONS

Participants kept sleep diaries and a regular time-in-bed schedule for 9 days, culminating in 2 consecutive nights of ambulatory polysomnography and a single proton MRS session. The main outcome measure was occipital GABA/creatine ratios; secondary measures included sleep measurements and relationship between polysomnographically measured time awake after sleep onset and occipital GABA content.

MEASUREMENTS AND RESULTS

The primary insomnia group was distinguished from persons with no sleep complaints on self-reported and polysomnographically measured sleep. The two groups did not differ in age, sex, body mass index, habitual bed- and wake-times, napping, use of caffeine, or use of cigarettes. Mean occipital GABA level was 12% higher in persons with insomnia than in persons without sleep complaints (P < 0.05). In both groups, GABA levels correlated negatively with polysomnographically measured time awake after sleep onset (P < 0.05).

CONCLUSIONS

Increased GABA levels in persons with insomnia may reflect an allostatic response to chronic hyperarousal. The preserved, negative relationship between GABA and time awake after sleep onset supports this notion, indicating that the possible allostatic response is adaptive.

Reduced γ-aminobutyric acid in occipital and anterior cingulate cortices in primary insomnia: a link to major depressive disorder?

Insomnia is closely related to major depressive disorder (MDD) both cross-sectionally and longitudinally, and as such, offers potential opportunities to refine our understanding of the neurobiology of both sleep and mood disorders. Clinical and basic science data suggest a role for reduced γ-aminobutyric acid (GABA) in both MDD and primary insomnia (PI). Here, we have utilized single-voxel proton magnetic spectroscopy (1H-MRS) at 4 Tesla to examine GABA relative to total creatine (GABA/Cr) in the occipital cortex (OC), anterior cingulate cortex (ACC), and thalamus in 20 non-medicated adults with PI (12 women) and 20 age- and sex-matched healthy sleeper comparison subjects. PI subjects had significantly lower GABA/Cr in the OC (p=0.0005) and ACC (p=0.03) compared with healthy sleepers. There was no significant difference in thalamic GABA/Cr between groups. After correction for multiple comparisons, GABA/Cr did not correlate significantly with insomnia severity measures among PI subjects. This study is the first to demonstrate regional reductions of GABA in PI in the OC and ACC. Reductions in GABA in similar brain regions in MDD using 1H-MRS suggest a common reduction in cortical GABA among PI and mood disorders.

[Frequently occurring sleep disorders]

Some sleep disorders are frequently found in the general population. The most common include restless legs syndrome, insomnia, and sleep apnea. These sleep disorders are well classified and can easily be diagnosed and treated. Since they are risk factors for cardiovascular and psychiatric disorders, early diagnosis and treatment are essential to prevent these sequelae. The impairments caused by these sleep disorders (e.g., due to daytime sleepiness, sleep disruption, or cognitive deficits) can result in a significant reduction in a person's quality of life. The diagnostic and therapeutic recommendations were taken from the S3 guideline "Nonrestorative sleep/sleep disorders" by the German Sleep Society. The levels of evidence were given according to the recommendations of the Oxford Centre for Evidence-based Medicine.

Influence of work shift on glutamic acid and gamma-aminobutyric acid (GABA): evaluation with proton magnetic resonance spectroscopy at 3T

Working conditions such as shift work constitute a well-known risk factor for insomnia and excessive daytime sleepiness complaints. We compared brain gamma-aminobutyric acid (GABA), glutamic acid (Glu), glutamine (Gln), and Glx (Glu+Gln) levels in day-shift versus alternate-shift workers with proton magnetic resonance spectroscopy ((1)H-MRS) at 3T. The study population consisted of 32 healthy adult volunteers (16 day-shift and 16 alternate-shift workers). Each subject underwent MRS conducted using a MEGA-PRESS sequence in the early morning and early evening on the same day. Spectroscopy voxels (3.0 cm × 3.0 cm × 3.0 cm) were placed in the frontal lobe and parieto-occipital lobe. The GABA/Cr ratio in the frontal lobe was significantly lower for the alternate-shift group than for the day-shift group in the early evening (1.885 vs. 0.875). For the other metabolite ratios (Gln/Cr and Glx/Cr), there were no significant differences between the two groups regardless of morning or evening schedule. Our preliminary finding represents a possible alteration of GABA content in the brain related to an irregular work schedule.

An Etiological Model for Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Kindling might represent a heuristic model for understanding the etiology of Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS). Kindling occurs when an organism is exposed repeatedly to an initially sub-threshold stimulus resulting in hypersensitivity and spontaneous seizure-like activity. Among patients with ME/CFS, chronically repeated low-intensity stimulation due to an infectious illness might cause kindling of the limbic-hypothalamic-pituitary axis. Kindling might also occur by high-intensity stimulation (e.g., brain trauma) of the limbic-hypothalamic-pituitary axis. Once this system is charged or kindled, it can sustain a high level of arousal with little or no external stimulus and eventually this could lead to hypocortisolism. Seizure activity may spread to adjacent structures of the limbic-hypothalamic-pituitary axis in the brain, which might be responsible for the varied symptoms that occur among patients with ME/CFS. In addition, kindling may also be responsible for high levels of oxidative stress, which has been found in patients with ME/CFS.

Autonomic activation in insomnia: the case for acupuncture

Current conceptualizations of the biological basis for insomnia typically invoke central nervous system and/or autonomic nervous system arousal. Acupuncture may represent a unique avenue of treatment for poor sleep by virtue of its direct effects on peripheral nerves and muscles, which, in turn, modulate autonomic tone and central activation. In this review, we summarize both basic and clinical research indicating that acupuncture exerts profound influences via a wide variety of potential neural and/or hormonal mechanisms that have great relevance for the modulation of sleep and wakefulness. We illustrate principles of acupuncture intervention applied to cases of otherwise intractable insomnia that document successful application of this component of Traditional Chinese Medicine to the treatment of poor sleep. Our review indicates the necessity for further research in the relationship between the effects of acupuncture on insomnia and autonomic regulation, which might guide better selective use of this treatment modality for insomnia.

Is disturbed intracortical excitability a stable trait of chronic insomnia? A study using transcranial magnetic stimulation before and after multimodal sleep therapy

BACKGROUND

Chronic insomnia is a poorly understood disorder. Risk factors for developing chronic insomnia are largely unknown, yet disturbances in brain indexes of arousal seem to accompany the disorder. We here investigate whether insomnia patients and control participants differ with respect to brain responses to direct stimulation, i.e., cortical excitability. Transcranial magnetic stimulation (TMS) offers a method to directly investigate the excitability level of the human cerebral cortex in psychiatric and neurological disease.

METHODS

We investigated cortical excitability in 16 insomnia patients and 14 carefully matched control participants using absolute and relative amplitudes of motor evoked potentials in response to single- and paired-pulse stimulation using TMS.

RESULTS

Nonmedicated insomnia patients showed, first, an exaggerated absolute response to both suprathreshold single- and paired-pulse stimulation compared with control participants and second, a reduced relative response to paired-pulse stimulation at long interpulse intervals (i.e., a reduced intracortical facilitation). The abnormal excitability persisted despite sleep therapy that effectively improved sleep quality as well as behavioral and neuroimaging indexes of brain function.

CONCLUSIONS

The results suggest that a subtly disturbed intracortical excitability characterizes patients with chronic insomnia: a relatively reduced intracortical facilitation in the context of a globally increased absolute excitability. The findings do not resemble TMS findings after sleep deprivation or in sleep apnea and thus seem specific to insomnia. They may offer diagnostic value and implications for assessment of risk to develop this common and disabling disorder.

Insomnia and health-related quality of life

Health-related Quality of Life (HRQoL) has become an important construct in contemporary medicine and health care, permitting assessment of disorder burden and evaluation of interventions on various aspects of functioning, in a standardized manner. Here we review literature on the measurement of HRQoL in insomnia populations, and the extent to which insomnia treatment improves domains of HRQoL. It is concluded from the relatively small literature that insomnia impacts on diverse areas of HRQoL, and that both pharmacological and non-pharmacological interventions can produce, to varying degrees, improvements in domains spanning physical, social and emotional functioning. Limitations of the current literature are identified; with particular emphasis on measurement and conceptual shortcomings. Suggestions are made in relation to improving the quality of future research, and how to further shed light on the impact of insomnia - and treatment thereof - on both HRQoL and global quality of life.

Neurobiological Mechanisms In Chronic Insomnia

This article grapples with the notion that insomnia can or should be defined in physiologic terms. It is proposed that insomnia is better understood from a neurobiological perspective. A review of the neurobiology of sleep and wakefulness is provided with a special emphasis on the implications for insomnia. Following the review it is suggested that a complete understanding of insomnia will require that the neurobiologic characterization of insomnia be informed by modern cognitive concepts and methods.

Hyperarousal and insomnia: state of the science

In the past few years it has become increasingly clear that insomnia is a chronic disease that interacts with many other medical conditions. As our ability to examine complex physiological activity during sleep has increased, additional evidence continues to suggest that insomnia is associated with inappropriate physiological arousal. It is now known that patients with primary insomnia have increased high-frequency EEG activation, abnormal hormone secretion, increased whole body and brain metabolic activation, and elevated heart rate and sympathetic nervous system activation during sleep. This activation can be measured throughout the day and night and is chronic. Other research suggests that insomnia, probably based upon the associated chronic physiologic arousal, is associated with increased risk for medical disorders such as depression, hypertension, or cardiac disease. An animal model that has used odor stress to produce poor sleep in rats has identified specific activated brain sites similar to those found in human brain metabolic studies to suggest that insomnia is a state in which sleep and arousal systems are both simultaneously active. The animal studies have also shown that the inappropriate arousal can be blocked by lesions in the limbic and arousal systems. It is hoped that these findings can be extended to identify new compounds that improve insomnia by acting at these sites of abnormal brain activation.

The hyperarousal model of insomnia: a review of the concept and its evidence

Primary insomnia is defined as difficulties in falling asleep, maintaining sleep or non-restorative sleep accompanied by significantly impaired daytime functioning in the absence of a specific physical, mental or substance-related cause. The current review provides substantial support for the concept that hyperarousal processes from the molecular to the higher system level play a key role in the pathophysiology of primary insomnia. Autonomous, neuroendocrine, neuroimmunological, electrophysiological and neuroimaging studies demonstrate increased levels of arousal in primary insomnia during both night and daytime. In the light of neurobiological theories of sleep-wake regulation, primary insomnia may be conceptualized as a final common pathway resulting from the interplay between a genetic vulnerability for an imbalance between arousing and sleep-inducing brain activity, psychosocial/medical stressors and perpetuating mechanisms including dysfunctional sleep-related behavior, learned sleep preventing associations and other cognitive factors like tendency to worry/ruminate.

Kindling and Oxidative Stress as Contributors to Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS) is one of the more complex illnesses involving multiple systems within the body. Onset of ME/CFS frequently occurs quickly, and many patients report a prior exposure to a viral infection. This debilitating illness can affect the immune, neuroendocrine, autonomic, and neurologic systems. Abnormal biological findings among some patients have included aberrant ion transport and ion channel activity, cortisol deficiency, sympathetic nervous system hyperactivity, EEG spike waves, left ventricular dysfunction in the heart, low natural killer cell cytotoxicity, and a shift from Th1 to Th2 cytokines. We propose that the kindling and oxidative stress theories provide a heuristic template for better understanding the at times conflicting findings regarding the etiology and pathophysiology of this illness.