Applications of transcranial magnetic stimulation in sleep medicine

Altered functional connectivity of the default mode and frontal control networks in patients with insomnia

AIMS

The purpose of this study was to investigate the association between spontaneous regional activity and brain functional connectivity, which maybe can distinguish insomnia while being responsive to repetitive transcranial magnetic stimulation (rTMS) treatment effects in insomnia patients.

METHODS

Using resting-state functional magnetic resonance imaging data from 38 chronic insomnia patients and 36 healthy volunteers, we compared the amplitude of low-frequency fluctuations (ALFF) between the two groups. Of all the patients with insomnia, 20 received rTMS for 4 weeks, while 18 patients received a 4-week pseudo-stimulation intervention. Seed-based resting-state functional connectivity (RSFC) analysis was conducted from regions with significantly different ALFF values, and the association between RSFC value and Pittsburgh Sleep Quality Index score was determined.

RESULTS

Our results revealed that insomnia patients presented a significantly higher ALFF value in the posterior cingulate cortex (PCC), whereas a significantly lower ALFF value was observed in the superior parietal lobule (SPL). Moreover, significantly reduced RSFC was detected from both PCC to prefrontal cortex connections, as well as from left SPL to frontal pole connections. In addition, RSFC from frontal pole to left SPL negatively predicted sleep quality (PSQI) and treatment response in patients' group.

CONCLUSION

Our findings suggest that disrupted frontoparietal network connectivity may be a biomarker for insomnia in middle-aged adults, reinforcing the potential of rTMS targeting the frontal lobes. Monitoring pretreatment RSFC could offer greater insight into how rTMS treatments are responded to by insomniacs.

Repetitive transcranial magnetic stimulation in primary sleep disorders

Repetitive transcranial magnetic stimulation (rTMS) is a widely used non-invasive neuromodulatory technique. When applied in sleep medicine, the main hypothesis explaining its effects concerns the modulation of synaptic plasticity and the strength of connections between the brain areas involved in sleep disorders. Recently, there has been a significant increase in the publication of rTMS studies in primary sleep disorders. A multi-database-based search converges on the evidence that rTMS is safe and feasible in chronic insomnia, obstructive sleep apnea syndrome (OSAS), restless legs syndrome (RLS), and sleep deprivation-related cognitive deficits, whereas limited or no data are available for narcolepsy, sleep bruxism, and REM sleep behavior disorder. Regarding efficacy, the stimulation of the dorsolateral prefrontal cortex bilaterally, right parietal cortex, and dominant primary motor cortex (M1) in insomnia, as well as the stimulation of M1 leg area bilaterally, left primary somatosensory cortex, and left M1 in RLS reduced subjective symptoms and severity scale scores, with effects lasting for up to weeks; conversely, no relevant effect was observed in OSAS and narcolepsy. Nevertheless, several limitations especially regarding the stimulation protocols need to be considered. This review should be viewed as a step towards the further contribution of individually tailored neuromodulatory techniques for sleep disorders.

Sleep and homeostatic control of plasticity

Sleep homeostasis is a complex neurobiologic phenomenon involving a number of molecular pathways, neurotransmitter release, synaptic activity, and factors modulating neural networks. Sleep plasticity allows for homeostatic optimization of neural networks and the replay-based consolidation of specific circuits, especially important for cognition, behavior, and information processing. Furthermore, research is currently moving from an essentially brain-focused to a more comprehensive view involving other systems, such as the immune system, hormonal status, and metabolic pathways. When dysfunctional, these systems contribute to sleep loss and fragmentation as well as to sleep need. In this chapter, the implications of neural plasticity and sleep homeostasis for the diagnosis and treatment of some major sleep disorders, such as insomnia and sleep deprivation, obstructive sleep apnea syndrome, restless legs syndrome, REM sleep behavior disorder, and narcolepsy are discussed in detail with their therapeutical implications. This chapter highlights that sleep is necessary for the maintenance of an optimal brain function and is sensitive to both genetic background and environmental enrichment. Even in pathologic conditions, sleep acts as a resilient plastic state that consolidates prior information and prioritizes network activity for efficient brain functioning.

Contribution of brainstem circuits in pathophysiology of NREM-sleep parasomnias

OBJECTIVE

We aimed to investigate the brainstem circuits to reveal if there was any abnormality in these circuits in clinically diagnosed patients with NREM parasomnias during wakefulness.

METHODS

Twelve patients with NREM-sleep parasomnia diagnosed according to ICSD-3 criteria and a control group of 16 healthy subjects were enrolled into our study. We analyzed the auditory startle reflex (ASR), blink reflex (BR), prepulse inhibition (PPI) of BR and recovery excitability of BR.

RESULTS

There was a trend for longer responses from orbicularis oculi and sternocleidomastoid muscles after auditory stimulation in the patients compared to those in the healthy subjects. The recovery percentages at 200 ms and 300 ms showed a borderline significance in the patients. No significant difference was found in the R2-PPI between the patients and healthy subjects.

CONCLUSIONS

Our results suggest a mildly enhanced ASR and relatively early facilitation of BR excitability in patients with NREM-sleep parasomnia during daytime. Although our findings suggest involvement of brainstem networks in NREM-sleep parasomnia during wakefulness, it would be better to study these networks at night and during daytime to see if there is any contribution.

New potential stimulation targets for noninvasive brain stimulation treatment of chronic insomnia

BACKGROUND

Noninvasive brain stimulation (NIBS) was recently used as a therapeutic application in patients with insomnia. Most of the previous NIBS treatments for insomnia directly selected the dorsolateral prefrontal cortex (DLPFC) as the stimulation site. As the NIBS target is an important factor in the efficacy of NIBS, it is necessary to detect more potential cortical sites for NIBS in insomnia.

METHODS

A neuroimaging study-based meta-analysis was used to examine sleep-related brain regions. A sleep-associated brain region-based functional connectivity (FC) map was constructed in 50 patients with chronic insomnia disorder (CID) without any comorbidity. We also combined the meta-analysis and FC results to examine the potential surface targets for NIBS for CID.

RESULTS

The results identified the bilateral supplementary motor area (SMA), left superior temporal gyrus (STG), bilateral DLPFC, precentral lobule, supramarginal gyrus, angular gyrus, superior frontal gyrus, middle temporal gyrus and middle occipital gyrus as potential brain stimulation targets for insomnia treatment. Notably, the bilateral SMA, right DLPFC and left STG were identified in the FC and meta-analyses. In addition, the SMA and DLPFC were positively and STG was negatively connected with other sleep related brain regions, which indicated inhibitory and excitatory stimulation for NIBS treatment for CID, respectively.

CONCLUSION

Our study suggests the SMA, DLPFC and STG as preferentially selected brain targets of NIBS for CID treatment. We recommend an inhibitory stimulation over SMA and DLPFC, and an excitatory stimulation over STG for NIBS treatment. Future studies should test these new targets using NIBS treatment for insomnia.

The effect of repetitive transcranial magnetic stimulation for insomnia: a systematic review and meta-analysis

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) might be a promising technique in treating insomnia. A comprehensive meta-analysis of the available literature is conducted to offer evidence.

OBJECTIVE

To evaluate the efficacy and safety of rTMS for insomnia, either as monotherapy or as a complementary strategy.

METHODS

CENTRAL, PubMed, EMBASE, PsycINFO, CINAHL, PEDro, CBM, CNKI, WANFANG, and VIP were searched from earliest record to August 2019. Randomized control trials (RCTs) published in English and Chinese examining effects of rTMS on patients with insomnia were included. Two authors independently completed the article selection, data extraction and rating. Physiotherapy Evidence Database (PEDro) scale was used to assess the methodological quality of the included studies. The RevMan software was used for meta-analysis. The quality of the evidence was assessed by Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

RESULTS

A total of 36 trials from 28 eligible studies were included, involving a total of 2357 adult participants (mean age, 48.80 years; 45.33% males). Compared with sham rTMS, rTMS was associated with improved PSQI total score (SMD -2.31, 95% CI -2.95 to -1.66; Z = 7.01, P < 0.00001) and scores of seven subscales. Compared to other treatment, rTMS as an adjunct to other treatment was associated with improved PSQI total score (SMD -1.44, 95% CI -2.00 to -0.88; Z = 5.01, P < 0.00001), and may have effects on scores of seven subscales. Compared with other treatment, rTMS was associated with improved Pittsburgh sleep quality index (PSQI) total score (SMD -0.63, 95% CI -1.22 to -0.04; Z = 2.08, P = 0.04), and may have a better score in sleep latency, sleep disturbance and hypnotic using of seven subscales. In the three pair of comparisons, the results for polysomnography (PSG) outcomes were varied. In general, rTMS may improve sleep quality through increasing slow wave and rapid eye movement (REM) sleep. The rTMS group was more prone to headache than the sham or blank control group (RR 1.71, 95% CI 1.03 to 2.85; Z = 2.07, P = 0.04). No severe adverse events were reported. Reporting biases and low and very low grade of some evidences should be considered when interpreting the results of this meta-analysis.

CONCLUSIONS

Our findings indicate that rTMS may be a safe and effective option for insomnia. Further international, multicenter, high-quality RCTs with more objective, quality of life related and follow-up assessments are needed.

Excessive Daytime Sleepiness in Parkinson's Disease: Clinical Implications and Management

Objective

Excessive daytime sleepiness (EDS) is one of the most common sleep abnormalities in patients with Parkinson's disease (PD), yet its multifactorial etiology complicates its treatment. This review summarized recent studies on the epidemiology, etiology, clinical implications, associated features, and evaluation of EDS in PD. The efficacy of pharmacologic and non-pharmacologic treatments for EDS in PD was also reviewed.

Data Sources

English language articles indexed in PubMed and Cochrane databases and Chinese-language papers indexed in Wanfang and National Knowledge Infrastructure databases that were published between January 1987 and November 2017 were located using the following search terms: "sleepiness", "sleep and Parkinson's disease", and "Parkinson's disease and treatment".

Study Selection

Original research articles and critical reviews related to EDS in PD were selected.

Results

EDS is a major health hazard and is associated with many motor and nonmotor symptoms of PD. Its causes are multifactorial. There are few specific guidelines for the treatment of EDS in PD. It is first necessary to identify and treat any possible factors causing EDS. Recent studies showed that some nonpharmacologic (i.e., cognitive behavioral therapy, light therapy, and repetitive transcranial magnetic stimulation) and pharmacologic (i.e., modafinil, methylphenidate, caffeine, istradefylline, sodium oxybate, and atomoxetine) treatments may be effective in treating EDS in PD.

Conclusions

EDS is common in the PD population and can have an immensely negative impact on quality of life. Its causes are multifactorial, which complicates its treatment. Further investigations are required to determine the safety and efficacy of potential therapies and to develop novel treatment approaches for EDS in PD.

Optimization of multiple coils immersed in a conducting liquid for half-hemisphere or whole-brain deep transcranial magnetic stimulation: a simulation study

Transcranial magnetic stimulation (TMS) was proposed in 1985. Nevertheless, its wider use in the treatment of several neurologic diseases has been hindered by its inability to stimulate deep-brain regions. This is mainly due to the physical limiting effect arising from the presence of surface discontinuities, particularly between the scalp and air. Here, we present the optimization of a system of large multiple coils for whole-brain and half-hemisphere deep TMS, termed orthogonal configuration. COMSOL(®)-based simulations show that the system is capable of reaching the very center of a spherical brain phantom with 58% induction relative to surface maximum. Such penetration capability surpasses to the best of our knowledge that of existing state of the art TMS systems. This induction capability strongly relies on the immersion of the stimulating coils and part of the head of the patient in a conducting liquid (e.g. simple saline solution). We show the impact of the presence of this surrounding conducting liquid by comparing the performance of our system with and without such liquid. In addition, we also compare the performance of the proposed coil with that of a circular coil, a figure-eight coil, and the H-coil. Finally, in addition to its whole-brain stimulation capability (e.g. potentially useful for prophylaxis of epileptic patients) the system is also able to stimulate mainly one brain hemisphere, which may be useful in stroke rehabilitation, among other applications.

Pharmacological treatment of sleep disorders and its relationship with neuroplasticity

Sleep and wakefulness are regulated by complex brain circuits located in the brain stem, thalamus, subthalamus, hypothalamus, basal forebrain, and cerebral cortex. Wakefulness and NREM and REM sleep are modulated by the interactions between neurotransmitters that promote arousal and neurotransmitters that promote sleep. Various lines of evidence suggest that sleep disorders may negatively affect neuronal plasticity and cognitive function. Pharmacological treatments may alleviate these effects but may also have adverse side effects by themselves. This chapter discusses the relationship between sleep disorders, pharmacological treatments, and brain plasticity, including the treatment of insomnia, hypersomnias such as narcolepsy, restless legs syndrome (RLS), obstructive sleep apnea (OSA), and parasomnias.

Increased electroencephalographic high frequencies during the sleep onset period in patients with restless legs syndrome

STUDY OBJECTIVES

To analyze the electroencephalographic (EEG) spectral content in untreated patients with restless legs syndrome (RLS) during the sleep onset period (SOP) and during the quiet wakefulness preceding sleep, in order to test the hypothesis that a state of hyperarousal might be present during the SOP with RLS.

SETTING

Sleep Research Centre.

PATIENTS

Twenty-seven untreated consecutive patients with RLS (mean age = 53.6 y), 11 untreated consecutive patients with primary insomnia (mean age = 58.9 y), and 14 normal controls (mean age = 50.3 y).

METHODS

SOP was defined as the 10-min period centered with the occurrence of the first sleep spindle in the EEG, and then subdivided into SOP-1 (period of 5 min before the first spindle) and SOP-2 (period of 5 min following). Leg movements occurring during SOP were counted and used as a covariate in the statistical analysis. Also, one period of 1 min of artifact-free quiet wakefulness after lights off was identified. EEG spectral analysis was run during these periods using the C3/A2 or C4/A1 channel.

MEASUREMENTS AND RESULTS

Increased EEG alpha and beta bands and/or beta/delta ratio in RLS versus normal controls, during both wakefulness preceding sleep and SOP (both parts SOP-1 and SOP-2) were found, which were, however, smaller than the increases found in patients with insomnia.

CONCLUSION

The results of this study support the hypothesis of the presence of a state of hyperarousal in restless legs syndrome (RLS) during the sleep onset period. Treatment for RLS might need to take these findings into consideration.

CITATION

Ferri R, Cosentino FI, Manconi M, Rundo F, Bruni O, Zucconi M. Increased electroencephalographic high frequencies during the sleep onset period in patients with restless legs syndrome.

Numerical modelling of plasticity induced by transcranial magnetic stimulation

We use neural field theory and spike-timing dependent plasticity to make a simple but biophysically reasonable model of long-term plasticity changes in the cortex due to transcranial magnetic stimulation (TMS). We show how common TMS protocols can be captured and studied within existing neural field theory. Specifically, we look at repetitive TMS protocols such as theta burst stimulation and paired-pulse protocols. Continuous repetitive protocols result mostly in depression, but intermittent repetitive protocols in potentiation. A paired pulse protocol results in depression at short ( < ∼ 10 ms) and long ( > ∼ 100 ms) interstimulus intervals, but potentiation for mid-range intervals. The model is sensitive to the choice of neural populations that are driven by the TMS pulses, and to the parameters that describe plasticity, which may aid interpretation of the high variability in existing experimental results. Driving excitatory populations results in greater plasticity changes than driving inhibitory populations. Modelling also shows the merit in optimizing a TMS protocol based on an individual's electroencephalogram. Moreover, the model can be used to make predictions about protocols that may lead to improvements in repetitive TMS outcomes.

Transcranial magnetic stimulation and sleep disorders: pathophysiologic insights

The neural mechanisms underlying the development of the most common intrinsic sleep disorders are not completely known. Therefore, there is a great need for noninvasive tools which can be used to better understand the pathophysiology of these diseases. Transcranial magnetic stimulation (TMS) offers a method to noninvasively investigate the functional integrity of the motor cortex and its corticospinal projections in neurologic and psychiatric diseases. To date, TMS studies have revealed cortical and corticospinal dysfunction in several sleep disorders, with cortical hyperexcitability being a characteristic feature in some disorders (i.e., the restless legs syndrome) and cortical hypoexcitability being a well-established finding in others (i.e., obstructive sleep apnea syndrome narcolepsy). Several research groups also have applied TMS to evaluate the effects of pharmacologic agents, such as dopaminergic agent or wake-promoting substances. Our review will focus on the mechanisms underlying the generation of abnormal TMS measures in the different types of sleep disorders, the contribution of TMS in enhancing the understanding of their pathophysiology, and the potential diagnostic utility of TMS techniques. We also briefly discussed the possible future implications for improving therapeutic approaches.

Left dorsolateral prefrontal transcranial magnetic stimulation (TMS): sleep factor changes during treatment in patients with pharmacoresistant major depressive disorder

As they alleviate major depressive disorder, antidepressant therapies may improve associated sleep disturbances, but may also have inherent sedating or activating properties. We examined sleep changes during a multicenter, sham-controlled, trial of transcranial magnetic stimulation (TMS) therapy for pharmacoresistant MDD. Medication-free outpatients (N=301) were randomized to receive active (N=155) or sham (N=146) TMS for 6 weeks. Depression severity was rated with the Montgomery-Asberg Depression Rating Scale, the 24-item Hamilton Depression Scale (HAMD), and the Inventory of Depressive Symptoms-Self Report (IDS-SR). Assessments were performed at baseline, 2, 4, and 6 week time points. Sleep was assessed using the HAMD and IDS-SR sleep factors; comparison between treatment groups employed ANCOVA model. No significant differences were identified between the active and sham treatment groups in either the HAMD or IDS-SR sleep factor scores at any time during treatment. Sleep difficulty as an adverse event over the length of the study did not differ between active and sham treatment. Stratified by end of acute treatment responder status, there was a statistically significant improvement in both the HAMD sleep factor score and the IDS-SR sleep factor during acute treatment in both the active and sham treatment conditions. TMS exerts no intrinsic effect upon sleep in patients with MDD.

Can transcranial magnetic stimulation be used to evaluate patients with narcolepsy?

Narcolepsy is a rare, chronic sleep disorder characterized by excessive daytime sleepiness, cataplexy and other manifestations of dissociated rapid eye movement in sleep. We assessed the utility of transcranial magnetic stimulation (TMS) as an objective tool to elucidate the cortical excitability changes and also to analyze its role in assessing the treatment efficacy in narcolepsy. Eight patients with narcolepsy under our regular follow-up from 2000 to 2009 at our Sleep disorder clinic were chosen. All of them underwent polysomnography, multiple sleep latency tests and TMS. Resting motor threshold (RMT), cortical silent period (CSP) and central motor conduction time (CMCT) were assessed using TMS in both drug-naïve and post-treatment states. Eight controls were also subjected to all the three investigations. Appropriate statistical methods were used. The mean RMT (%) pre-treatment was higher in narcolepsy patients than that in controls, and it normalized following treatment. CSP and CMCT were unaffected in narcolepsy patients as compared to controls. This study shows that the cortical excitability is significantly low in narcolepsy patients. This motor cortex hypoexcitability becomes normal with the institution of treatment, pari passu with the control of symptoms. In future, TMS may be considered as an effective tool for documenting the treatment efficacy in patients with narcolepsy.

Cırcadian changes in cortical excitability in restless legs syndrome

Various investigations have revealed a widespread and somewhat controversial pattern of cerebral, cerebellar and brainstem involvement in the pathophysiology of restless legs syndrome (RLS). However, several studies which investigated functional or structural aspects indicated cortical involvement in RLS. In this study, we aimed to analyze circadian changes of cortical excitability in idiopathic RLS patients by means of transcranial magnetic stimulation (TMS). Eleven idiopathic RLS patients and eight healthy age and sex matched subjects were investigated using single-pulse TMS and motor nerve conduction studies during early afternoon when there were no symptoms and late at night (22:00-23:00) when the symptoms reappeared. Central motor conduction time, latencies and amplitudes of scalp and cervical motor evoked potentials, resting and active motor thresholds, and cortical silent period were measured. Measured parameters were similar between RLS patients and healthy subjects during the daytime. At night, cortical silent periods tended to shorten, and motor thresholds tended to decrease in the RLS group, whereas in controls they tended to increase. At night, active motor-threshold measurements were significantly lower in the RLS group (28.5 ± 6.2% vs 40.4 ± 8.4%, p=0.006). Therefore, we propose that in patients with RLS, conduction along the motor corticospinal axons is normal, with the possible loss of subcortical inhibition at nighttime.

Modafinil reverses hypoexcitability of the motor cortex in narcoleptic patients: a TMS study

OBJECTIVE

Although many animal and human studies have been performed, the exact mechanisms of action whereby modafinil promotes wakefulness are still not completely understood. We aimed to investigate the functional effects of modafinil on motor cortex excitability in patients with narcolepsy by means of transcranial magnetic stimulation (TMS) techniques.

METHODS

In a double-blind and placebo-controlled design, 24 drug-naive narcoleptic patients with cataplexy and 20 control subjects were administered modafinil or placebo over a period of 4 weeks. TMS was performed twice during the awake state before and at the end of treatment; measures of cortical excitability included central motor conduction time, resting motor threshold, short latency intracortical inhibition (SICI) and intracortical facilitation to paired-TMS. TMS measures were correlated with the conventional neurophysiological method of Multiple Sleep Latency Test (MSLT) and the subjective Epworth Sleepiness Scale (ESS).

RESULTS

As previously reported, motor threshold and SICI were significantly increased in patients with narcolepsy; modafinil reversed this cortical hypoexcitability, but only SICI differences reached statistical significance. The Spearman rank correlation analysis revealed the highest correlation between SICI and the MSLT; a positive correlation was also found between SICI and the ESS, as well as between RMT and both measures of daytime sleepiness.

CONCLUSIONS

This represents the first report investigating effects of modafinil on cortical excitability in human narcolepsy. Since SICI is thought to be directly related to GABA(A) intracortical inhibitory activity, we demonstrated that the dose of modafinil that induces a satisfactory wakefulness-promoting response in narcoleptic patients also causes decrease in GABAergic transmission.