[Show abstract][Hide abstract] ABSTRACT: Sleep has been shown to promote memory consolidation driven by certain oscillatory patterns, such as sleep spindles. However, sleep does not consolidate all newly encoded information uniformly but rather "selects" certain memories for consolidation. It is assumed that such selection depends on salience tags attached to the new memories before sleep. However, little is known about the underlying neuronal processes reflecting presleep memory tagging. The current study sought to address the question as to whether event-related changes in spectral theta power (theta ERSP) during presleep memory formation could reflect memory tagging that influences subsequent consolidation during sleep. Twenty-four participants memorized 160 word pairs before sleep; in a separate laboratory visit, they performed a nonlearning control task. Memory performance was tested twice, directly before and after 8 hr of sleep. Results indicate that participants who improved their memory performance overnight displayed stronger theta ERSP during the memory task in comparison with the control task. They also displayed stronger memory task-related increases in fast sleep spindle activity. Furthermore, presleep theta activity was directly linked to fast sleep spindle activity, indicating that processes during memory formation might indeed reflect memory tagging that influences subsequent consolidation during sleep. Interestingly, our results further indicate that the suggested relation between sleep spindles and overnight performance change is not as direct as once believed. Rather, it appears to be mediated by processes beginning during presleep memory formation. We conclude that theta ERSP during presleep memory formation reflects cortico-hippocampal interactions that lead to a better long-term accessibility by tagging memories for sleep spindle-related reprocessing.
[Show abstract][Hide abstract] ABSTRACT: Background Numerous studies indicate that K-complexes (KC), like slow waves, appear to be homeostatically regulated. In comparison to healthy controls, patients suffering from obstructive sleep apnea syndrome (OSAS) show a different time course of slow wave activity (SWA), enhanced sleep pressure, and impaired restorative sleep function. Objective The main goal of this study was to investigate homeostatic sleep regulation based on KC amplitude in sleep stage 2 in OSAS, prior to and under continuous positive airway pressure (CPAP) treatment. Subjects and methods The study participants comprised 22 patients suffering from OSAS (mean age of 59.7 years) and 22 age- and gender-matched healthy controls selected from the SIESTA database (mean age 59.3 years). Patients had one polysomnography (PSG) night before the start of CPAP treatment and one after 3-6 months of treatment. KC detection in sleep stage 2 was based on a validated automatic KC detection algorithm. Results As expected, in untreated patients, the KC amplitudes did not decrease significantly during the course of the night. However, under CPAP treatment we observed a significant decrease in KC amplitudes from the first to the fourth quarter of the night, similar to healthy controls. Conclusion The present study confirms that KC amplitude can be considered as a marker for sleep homeostasis in healthy controls and patients.
Somnologie - Schlafforschung und Schlafmedizin 03/2015; 19(1):22-29. DOI:10.1007/s11818-015-0701-5
[Show abstract][Hide abstract] ABSTRACT: Objective The purpose of the present study was to analyse gender- and age-specific variations in microstructures of rapid eye movement (REM) sleep and to provide reference values for microstructures. Methods The results are based on Somnolyzer 24 × 7 (The Siesta Group Schlafanalyse GmbH., Vienna, Austria) evaluation of data from the SIESTA database. Data from 160 healthy subjects (74 men and 86 women; age range 20-95 years) were considered and a total of 11 REM sleep-related variables analysed. Results Some of the variables, i.e., REM and slow eye movement (SEM) density, SEM intensity and the REM sleep arousal index, are fairly constant across ages and do not differ between men and women. The atonia index shows gender-specific differences, but does not vary with age among healthy subjects; whereas REM intensity and the time in tonic REM sleep decrease with age, without differences between men and women. Time in stage R sleep (minutes and percentage of total sleep time, TST) and the time in phasic stage R sleep vary with both age and gender. Conclusion Given the relevance of sleep microstructures in research and potentially also in clinical studies, there is a need for reference values indicating the range of variation of these variables in healthy subjects. Reference values always have the limitation that they refer to the specific method of assessment. Where different detection algorithms are used, the reference values might vary. The reference values presented here—where necessary for men and women separately and/or stratified by age—refer to microstructures assessed by the feature extraction module of the Somnolyzer 24 × 7.
Somnologie - Schlafforschung und Schlafmedizin 03/2015; 19(1):12-21. DOI:10.1007/s11818-015-0700-6
[Show abstract][Hide abstract] ABSTRACT: Objective Numerous studies point to the involvement of sleep spindles and slow waves in memory processes, particularly in hippocampus-dependent declarative memory. We have shown previously that the overnight change in recall performance in a declarative word pair association task correlates significantly with increased spindle activity during the night after learning compared to a control night. The current study re-evaluates this relationship in detail and explores whether the observed positive correlation of two spindle parameters measured during stage 2 (S2) sleep with overnight stabilization depend on the time of night (early vs. late) and spindle type (fast vs. slow). Methods The study included 24 healthy volunteers aged 20–30 years. Two counterbalanced nights served as either control condition without intentional learning or as an experimental condition including a declarative memory task in the evening. Performance was tested directly after learning and in the following morning. Spindle detection was based on a validated automatic algorithm, providing density and intensity of slow (≤ 13 Hz) and fast (> 13 Hz) spindles per minute S2 sleep. To obtain spindle measures during the course of the night, the entire recording period was segmented into five 90-min parts. Results Significant correlations were observed between changes (experimental night minus control night) in spindle density (r = 0.44, p Conclusion The present study confirms the involvement of fast sleep spindles during S2 in declarative memory processes. Significant correlations with spindle retention are only seen in early S2 sleep and not during late S2 sleep. It remains to be investigated whether this effect is due to circadian factors, homeostatic factors, or the time elapsed after initial learning.
Somnologie - Schlafforschung und Schlafmedizin 02/2015; 19(1). DOI:10.1007/s11818-015-0699-8
[Show abstract][Hide abstract] ABSTRACT: This chapter presents normative data on healthy sleep, as measured by polysomnography (PSG), from "supernormal" subjects across the age range from 20 to about 90 years. The data originates from the SIESTA project database established in the late 1990s. While that data has been published and used in research in many ways, the novelty of the current analysis is (a) the focus on normative data following the latest sleep staging standard (AASM 2012), and (b) the results after narrowing down the data set by excluding outliers due to disturbed sleep pattern that can occur in a sleep lab and are thus not examples of "normal" sleep. Results demonstrate interesting dependencies of sleep architecture on age, in particular a reduction in total sleep time and changes in sleep stage distributions toward lighter sleep, which differ in detail between the two genders.
Advances in Experimental Medicine and Biology 01/2015; 821:93-100. DOI:10.1007/978-3-319-08939-3_13 · 1.96 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: There is growing evidence of the active involvement of sleep in memory consolidation. Besides hippocampal sharp wave-ripple complexes and sleep spindles, slow oscillations appear to play a key role in the process of sleep-associated memory consolidation. Furthermore, slow oscillation amplitude and spectral power increase during the night after learning declarative and procedural memory tasks. However, it is unresolved whether learning-induced changes specifically alter characteristics of individual slow oscillations, such as the slow oscillation up-state length and amplitude, which are believed to be important for neuronal replay. 24 subjects (12 men) aged between 20 and 30 years participated in a randomized, within-subject, multicenter study. Subjects slept on three occasions for a whole night in the sleep laboratory with full polysomnography. Whereas the first night only served for adaptation purposes, the two remaining nights were preceded by a declarative word-pair task or by a non-learning control task. Slow oscillations were detected in non-rapid eye movement sleep over electrode Fz. Results indicate positive correlations between the length of the up-state as well as the amplitude of both slow oscillation phases and changes in memory performance from pre to post sleep. We speculate that the prolonged slow oscillation up-state length might extend the timeframe for the transfer of initial hippocampal to long-term cortical memory representations, whereas the increase in slow oscillation amplitudes possibly reflects changes in the net synaptic strength of cortical networks.
PLoS ONE 12/2013; 8(12):e82049. DOI:10.1371/journal.pone.0082049 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Sleep disturbances are frequent and multifaceted and have serious consequences. They play an important role within psychiatric symptoms and disorders. On the one hand they may appear as a symptom of a disorder, which may also be a diagnostic criterion, as for example in affective disorders, on the other hand they may be independent disorders or last but not least sequelae of psychiatric disorders or their pharmacological therapy, as with antidepressants or neuroleptics, which may cause or deteriorate nocturnal movement disorders. They may aggravate psychiatric disorders, perpetuate them or predict a disease onset, like in depressive or manic episodes. Also in organic sleep disorders, such as sleep-related breathing disorders or nocturnal movement disorders, increased anxiety or depression scores may be observed. Patients suffering from sleep disorders do not only experience impaired well-being, but also show deteriorations in cognition and performance, have a higher risk of accidents, are generally more prone to health problems, have a higher sickness absence rate, seek medical help more often and thus are also an important socioeconomic factor. This is why sleep disorders should be taken seriously and treated adequately.
[Show abstract][Hide abstract] ABSTRACT: The past two decades have witnessed substantial progress in methodology and knowledge in sleep research all over the world. The paper at hand will present some recent local contributions to this field. The first is a European project (SIESTA) focusing on the creation of an automatic sleep classification system and a normative database, including polysomnographic (PSG) and psychometric measures, in order to make it possible to diagnose sleep-disordered patients as compared with and age- and sex-matched healthy controls between 20 and 95 years of age. Subsequently, two trials on nonorganic sleep disorders in generalized anxiety disorder (GAD) and bruxism, as well as two trials on organic sleep disorders, i.e. snoring/sleep-disordered breathing treated with a mandibular advancement device (I.S.T.) and restless legs syndrome treated with ropinirole and gabapentin, will be discussed.
[Show abstract][Hide abstract] ABSTRACT: The International Pharmaco-EEG Society (IPEG) presents guidelines summarising the requirements for the recording and computerised evaluation of pharmaco-sleep data in man. Over the past years, technical and data-processing methods have advanced steadily, thus enhancing data quality and expanding the palette of sleep assessment tools that can be used to investigate the activity of drugs on the central nervous system (CNS), determine the time course of effects and pharmacodynamic properties of novel therapeutics, hence enabling the study of the pharmacokinetic/pharmacodynamic relationship, and evaluate the CNS penetration or toxicity of compounds. However, despite the presence of robust guidelines on the scoring of polysomnography -recordings, a review of the literature reveals inconsistent -aspects in the operating procedures from one study to another. While this fact does not invalidate results, the lack of standardisation constitutes a regrettable shortcoming, especially in the context of drug development programmes. The present guidelines are intended to assist investigators, who are using pharmaco-sleep measures in clinical research, in an effort to provide clear and concise recommendations and thereby to standardise methodology and facilitate comparability of data across laboratories.
[Show abstract][Hide abstract] ABSTRACT: Functional network disruption in degenerative dementia has been reported. EEG coherence is used to assess functional connectivity between brain areas. Previous studies of Huntington's disease (HD) reported about electroencephalography (EEG) spectral power and source location, but coherence has not yet been examined.Objectives and AimsTo examine EEG intracortical functional connectivity in HD using low-resolution brain electromagnetic tomography (LORETA).Methods
In 55 HD patients and 55 controls, 3-minute 19-channel vigilance-controlled EEG was recorded, and recomputed to current densities of 6239 cortical sLORETA voxels. These were recomputed into source model time series for 19 regions of interest (ROIs). Coherence overestimation due to volume conduction was avoided by computing functional connectivity as ‘lagged’ coherence. This was done for each ROI pair (19*18/2=171) in each of 8 EEG frequency bands (delta through gamma). Statistics tested coherences (a) HD patients versus controls, and (b) HD patients in early versus late disease stages.Results(a) HD patients showed only reduced connectivities compared to controls (p < 0.05 corrected for multiple comparison), involving EEG theta, alpha-1-2 and beta1-2-3 frequency bands. The largest number of reduced connectivities occurred in alpha-1 (79 cases) and beta-2 (96 cases). (b) HD stage-1 versus stage-3-4 revealed only one significant difference.ConclusionsHD compared to controls showed massive reduction of functional connectivity. This occurred early and remained stable during disease progression. As in other dementing disorders, for example Alzheimer disease, the largest reduction concerned alpha and beta EEG frequencies. The results suggest a neocortical disconnection syndrome of a primarily subcortical disease.
European Psychiatry 12/2012; 27:1. DOI:10.1016/S0924-9338(12)74960-X · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objective: Rapid eye movements (REMs) are a cardinal feature of REM sleep and their rate ("density" -REMD) is an indicator of the intensity of a hypothetical "REM process" (analogous to spectral power in the delta range in NREM sleep). The generation of REMs is assumed to be controlled by cholinergic and/or glutamatergic systems and REMD correlates with cognitive functions in elderly subjects. Thus, REMD might be a biomarker of successful aging. REMD was reduced in healthy elderly subjects as compared to young controls, while slow eye movements (SEMs) did not show any trend across REM periods. However, those studies were limited due to the small number of subjects and need confirmation in larger samples allowing establishing age curves for REMD. The aim of the present study was to confirm these findings in a larger database, using an automatic detection algorithm. Methods: REM density (time of REMs/ time in stage REM) and REM intensity (sum of eye movement amplitudes/min REM sleep) were evaluated automatically. Moreover, the Atonia Index (ATI, Ferri et al. 2008) was quantified as a measure of REM sleep atonia. 160 healthy subjects from the SIESTA database (86 females, 74 males aged between 20 to 95 years) participated in this study. REM periods were defined according to the standard criteria and visually checked for apparently missing periods. The effects of REM period and age on the obtained measures were investigated by means non parametric tests (Spearman rank correlations, Friedman test for dependent samples). Results: There are significant differences in REMD between REM periods 1 to 4 (p< 0.001), which was reduced in REM period 1 (no significant differences between periods 2 to 4 (p=.803)). Age did not correlate significantly with REMD (R = -.102, p= .199), but moderately with REM intensity (R = -.272, p< 0.001). Neither SEMD (p = .446), nor SEM intensity (p = .688) differed significantly between REM periods, or correlated significantly with age. There is a significant difference in ATI between REM periods (declining over the night), but no significant correlation with age (R = .081). Results: As expected, we could confirm a reduced REMD during the 1st REM period and a significant aging effect in REM intensity but not REMD. Likewise, REM ATI increases during the night, but was not significantly affected by aging. Discussion: Computerized analysis of rapid and slow eye movements is a sensitive marker of the intensity of the REM process.
21st Congress of the European Sleep Research Society; 09/2012
[Show abstract][Hide abstract] ABSTRACT: Parkinson’s disease (PD) is often accompanied by dysfunctions of the autonomous nervous system (ANS). Heart rate variability (HRV) may impact on sleep regulation with regard to sympatho-vagal balance and sleep stages. This study analyzed possible differences in ANS activity between PD patients medicated with levodopa and a healthy control group in context with sleep.
Methods: In PD patients (N = 8) and controls (N = 11) polysomnographic (PSG) recordings were registered for two nights. To minimize a possible first night effect, only the second night was used. Electrocardiography (ECG) recordings were inspected by an automatic algorithm to detect R-R interval lengths, which were then analyzed via fast Fourier transformation. For use as a marker for sympatho-vagal balance, the resultant frequency ranges were subdivided into low frequency (LF, 0.04-0.15 Hz) and high frequency (HF, 0.15-0.4 Hz) sub-bands. In addition, ratio of LF and HF (LF/HF ratio) was calculated.
Results: LF was higher in controls compared to PD patients. Both groups showed significant variation, with peaks during wake and REM and troughs during NonREM sleep. Similarly, LF/HF ratio was lower in PD patients compared to controls, significantly so during Wake, Stage 1, Stage 2, and REM. On a group level, LF/HF ratio never exceeded the HRV of controls, but the difference was not significant. For HF, no significant changes were found in either group.
Conclusion: We conclude that PD reduces sympatho-vagal balance. The decrease in LF and LF/HF was especially distinctive during REM. This could be an effect of sympathetic degeneration in cardiac cells.
Keywords: Parkinson’s disease, autonomous nervous system, sleep, heart rate variability, levodopa
Movement Disorders 03/2012; 27(3):454. DOI:10.1002/mds.24897 · 5.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Earlier studies reported that subjective sleep quality correlates with objective polysomnographically measured sleep initiation and continuity, but less with sleep architecture.AimsThis study aimed to investigate relations between subjective and objective sleep in normals (N), insomnia comorbid with generalized anxiety disorder (G) and apnea (A).Methods
One hundred and seventy-seven normals (50.9±19.6a), 100 insomniac G patients (37.9±10.6a) and 51 A patients (51.3±9.7a) completed the self-rating scale for sleep and awakening quality (Saletu et al. 1997) regarding two polysomnographic nights analyzed by the Somnolyzer (Anderer et al. 2005). Correlations were calculated based on changes between the first (adaptation) and second polysomnographic night to diminish inter-individual variances of sleep perception.ResultsIn N, subjective sleep quality (S-QUA) demonstrated correlations (p < 0.01) with sleep efficiency (EFF), wake after sleep onset (WASO), S2, S1%, REM, S1, frequency of awakenings (FW), latency to continuous sleep (L-CONT), sleep latency (S-LAT) and slow-wave sleep, while awakening quality (A-QUA) showed weak (p < 0.05) correlations with EFF and WASO. Somatic complaints (S-COM) correlated (p < 0.05) with WASO and REM. In G, correlations (p < 0.01) were obtained between S-QUA and EFF, WASO, S2, L-CONT and S-LAT (p < 0.05), while A-QUA correlated with S2, WASO and EFF. In A, S-QUA correlated (p < 0.01) with EFF, S2, S1%, S2%, L-CONT, WASO and less (p < 0.05) with S-LAT and S1. A-QUA correlated with S2, S2% (p < 0.01), L-CONT and EFF (p < 0.05). S-COM correlated with S-CONT (p < 0.01) and S-LAT (p < 0.05).ConclusionEFF, WASO, S2 and less S-LAT determine good S-QUA in all groups.
European Psychiatry 12/2011; 26:2174. DOI:10.1016/S0924-9338(11)73877-9 · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: ELECTROPHYSIOLOGICAL NEUROIMAGING REVEALS RE-SET, RE-ACTIVATION AND REPROCESSING OF PROCEDURAL AND DECLARATIVE MEMORY TRACES DURING POSTTRAINING SLEEP
P. Anderer (1,2), G. Gruber (2), S. Parapatics (2), C. Sauter (3), G. Kloesch (3), M. Schabus (4), W. Klimesch (4), G.M.Saletu-Zyhlarz (1), B. Saletu (1), J. Zeitlhofer (3)
1) Department of Psychiatry and Psychotherapy, Medical University of Vienna,
2) The Siesta Group Schlafanalyse GmbH,
3) Department of Neurology, Medical Universitiy of Vienna, Vienna,
4) Department of Physiological Psychology, University of Salzburg, Salzburg, Austria
Objectives: Experience-dependent cortical plasticity observed during post-training sleep has been hypothesized to be part of the global process of memory consolidation. Combining the temporal resolution of microstructure detectors and the spatial resolution of low-resolution brain electromagnetic tomography (LORETA) makes it possible to investigate when and where the experience-dependent reactivation occurs under normal (undisturbed) sleeping conditions.
Methods: After an adaptation night, in the 2nd and 3rd night 48 young healthy volunteers were randomly assigned either to a control condition or to an experimental condition (declarative Memory task: paired-associate word list or procedural memory task: mirror tracing). Sleep stages and sleep microstructures (slow waves, spindles and theta bursts) were detected automatically by means of the Somnolyzer 24x7. Changes in LORETA sources (experimental minus control night) were correlated with changes in memory performance (morning minus evening recall).
Results: Overnight improvements in the mirror tracing task were correlated with increased slow-wave sources in the right posterior parietal cortex (r=.70,p< 0.01) during NREM sleep and with desynchronized (r=-.76,p< 0.01) and synchronized (r=.62,p< 0.01) rolandic mu rhythm sources during periods with theta bursts in REM sleep. Overnight improvements in the declarative memory task were significantly correlated with increased spindle sources (r= .52, p< .01) in frontal, temporal and cingulate brain regions.
Conclusions: The present study supports the hypotheses of (1) a use-dependent reset of synaptic plasticity during slow-wave sleep (restorative function), (2) an experience-dependent reactivation during spindle episodes (stabilizing function) and (3) an off-line neuronal reprocessing during REM sleep (improvement without further training for novel tasks)
European Psychiatry 12/2011; 26:1849-1849. DOI:10.1016/S0924-9338(11)73553-2 · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Scalp electric potentials (electroencephalogram; EEG) are contingent to the impressed current density unleashed by cortical pyramidal neurons undergoing post-synaptic processes. EEG neuroimaging consists of estimating the cortical current density from scalp recordings. We report a solution to this inverse problem that attains exact localization: exact low-resolution brain electromagnetic tomography (eLORETA). This non-invasive method yields high time-resolution intracranial signals that can be used for assessing functional dynamic connectivity in the brain, quantified by coherence and phase synchronization. However, these measures are non-physiologically high because of volume conduction and low spatial resolution. We present a new method to solve this problem by decomposing them into instantaneous and lagged components, with the lagged part having almost pure physiological origin.
Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences 10/2011; 369(1952):3768-84. DOI:10.1098/rsta.2011.0081 · 2.15 Impact Factor