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Sayk C, Saftien S, Koch N, Ngo HVV, Junghanns K, Wilhelm I. Cortical hyperarousal in individuals with frequent nightmares. J Sleep Res 2024; 33:e14003. [PMID: 37688512 DOI: 10.1111/jsr.14003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2023] [Revised: 06/09/2023] [Accepted: 07/01/2023] [Indexed: 09/11/2023]
Abstract
Nightmares are common among the general population and psychiatric patients and have been associated with signs of nocturnal arousal such as increased heart rate or increased high-frequency electroencephalographic (EEG) activity. However, it is still unclear, whether these characteristics are more of a trait occurring in people with frequent nightmares or rather indicators of the nightmare state. We compared participants with frequent nightmares (NM group; n = 30) and healthy controls (controls; n = 27) who spent 4 nights in the sleep laboratory over the course of 8 weeks. The NM group received six sessions of imagery rehearsal therapy (IRT), the 'gold standard' of cognitive-behavioural therapy for nightmares, between the second and the third night. Sleep architecture and spectral power were compared between groups, and between nights of nightmare occurrence and nights without nightmare occurrence in the NM group. Additionally, changes before and after therapy were recorded. The NM group showed increased beta (16.25-31 Hz) and low gamma (31.25-35 Hz) power during the entire night compared to the controls, but not when comparing nights of nightmare occurrence to those without. Moreover, low gamma activity in rapid eye movement sleep was reduced after therapy in the NM group. Our findings indicate, cortical hyperarousal is more of a trait in people with frequent nightmares within a network of other symptoms, but also malleable by therapy. This is not only a new finding for IRT but could also lead to improved treatment options in the future that directly target high-frequency EEG activity.
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Affiliation(s)
- Clara Sayk
- Department of Psychiatry and Psychotherapy, Translational Psychiatry Unit, University of Lübeck, Lübeck, Germany
| | - Sophia Saftien
- Department of Psychiatry and Psychotherapy, Translational Psychiatry Unit, University of Lübeck, Lübeck, Germany
| | - Nicole Koch
- Department of Psychiatry and Psychotherapy, Translational Psychiatry Unit, University of Lübeck, Lübeck, Germany
| | - Hong-Viet V Ngo
- Department of Psychology, University of Lübeck, Lübeck, Germany
- Center for Brain, Behaviour and Metabolism, University of Lübeck, Lübeck, Germany
- Department of Psychology, University of Essex, Colchester, UK
| | - Klaus Junghanns
- Department of Psychiatry and Psychotherapy, Translational Psychiatry Unit, University of Lübeck, Lübeck, Germany
| | - Ines Wilhelm
- Department of Psychiatry and Psychotherapy, Translational Psychiatry Unit, University of Lübeck, Lübeck, Germany
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Dudysová D, Janků K, Piorecký M, Hantáková V, Orendáčová M, Piorecká V, Štrobl J, Kliková M, Ngo HVV, Kopřivová J. Closed-loop auditory stimulation of slow-wave sleep in chronic insomnia: a pilot study. J Sleep Res 2024:e14179. [PMID: 38467353 DOI: 10.1111/jsr.14179] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2023] [Revised: 12/12/2023] [Accepted: 02/07/2024] [Indexed: 03/13/2024]
Abstract
Insomnia is a prevalent and disabling condition whose treatment is not always effective. This pilot study explores the feasibility and effects of closed-loop auditory stimulation (CLAS) as a potential non-invasive intervention to improve sleep, its subjective quality, and memory consolidation in patients with insomnia. A total of 27 patients with chronic insomnia underwent a crossover, sham-controlled study with 2 nights of either CLAS or sham stimulation. Polysomnography was used to record sleep parameters, while questionnaires and a word-pair memory task were administered to assess subjective sleep quality and memory consolidation. The initial analyses included 17 patients who completed the study, met the inclusion criteria, and received CLAS. From those, 10 (58%) received only a small number of stimuli. In the remaining seven (41%) patients with sufficient CLAS, we evaluated the acute and whole-night effect on sleep. CLAS led to a significant immediate increase in slow oscillation (0.5-1 Hz) amplitude and activity, and reduced delta (1-4 Hz) and sigma/sleep spindle (12-15 Hz) activity during slow-wave sleep across the whole night. All these fundamental sleep rhythms are implicated in sleep-dependent memory consolidation. Yet, CLAS did not change sleep-dependent memory consolidation or sleep macrostructure characteristics, number of arousals, or subjective perception of sleep quality. Results showed CLAS to be feasible in patients with insomnia. However, a high variance in the efficacy of our automated stimulation approach suggests that further research is needed to optimise stimulation protocols to better unlock potential CLAS benefits for sleep structure and subjective sleep quality in such clinical settings.
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Affiliation(s)
- Daniela Dudysová
- National Institute of Mental Health, Klecany, Czech Republic
- Third Faculty of Medicine, Charles University, Prague, Czech Republic
| | - Karolina Janků
- National Institute of Mental Health, Klecany, Czech Republic
| | - Marek Piorecký
- National Institute of Mental Health, Klecany, Czech Republic
- Faculty of Biomedical Engineering, Czech Technical University in Prague, Prague, Czech Republic
| | - Veronika Hantáková
- National Institute of Mental Health, Klecany, Czech Republic
- School of Medicine, Medical Sciences and Nutrition, University of Aberdeen, Aberdeen, Scotland
| | - Mária Orendáčová
- National Institute of Mental Health, Klecany, Czech Republic
- Third Faculty of Medicine, Charles University, Prague, Czech Republic
- Department of Physiology, Faculty of Science, Charles University in Prague, Prague, Czech Republic
| | - Václava Piorecká
- National Institute of Mental Health, Klecany, Czech Republic
- Faculty of Biomedical Engineering, Czech Technical University in Prague, Prague, Czech Republic
| | - Jan Štrobl
- National Institute of Mental Health, Klecany, Czech Republic
- Faculty of Biomedical Engineering, Czech Technical University in Prague, Prague, Czech Republic
| | - Monika Kliková
- National Institute of Mental Health, Klecany, Czech Republic
| | - Hong-Viet V Ngo
- Center for Brain, Behaviour and Metabolism, University of Lübeck, Lübeck, Germany
- Department of Psychology, University of Lübeck, Lübeck, Germany
- Department of Psychology, University of Essex, Colchester, UK
| | - Jana Kopřivová
- National Institute of Mental Health, Klecany, Czech Republic
- Third Faculty of Medicine, Charles University, Prague, Czech Republic
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3
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Esfahani MJ, Farboud S, Ngo HVV, Schneider J, Weber FD, Talamini LM, Dresler M. Closed-loop auditory stimulation of sleep slow oscillations: Basic principles and best practices. Neurosci Biobehav Rev 2023; 153:105379. [PMID: 37660843 DOI: 10.1016/j.neubiorev.2023.105379] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 08/25/2023] [Accepted: 08/30/2023] [Indexed: 09/05/2023]
Abstract
Sleep is essential for our physical and mental well-being. During sleep, despite the paucity of overt behavior, our brain remains active and exhibits a wide range of coupled brain oscillations. In particular slow oscillations are characteristic for sleep, however whether they are directly involved in the functions of sleep, or are mere epiphenomena, is not yet fully understood. To disentangle the causality of these relationships, experiments utilizing techniques to detect and manipulate sleep oscillations in real-time are essential. In this review, we first overview the theoretical principles of closed-loop auditory stimulation (CLAS) as a method to study the role of slow oscillations in the functions of sleep. We then describe technical guidelines and best practices to perform CLAS and analyze results from such experiments. We further provide an overview of how CLAS has been used to investigate the causal role of slow oscillations in various sleep functions. We close by discussing important caveats, open questions, and potential topics for future research.
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Affiliation(s)
| | - Soha Farboud
- Donders Institute for Brain, Cognition and Behaviour, Radboud University, the Netherlands
| | - Hong-Viet V Ngo
- Department of Psychology, University of Essex, United Kingdom; Department of Psychology, University of Lübeck, Germany; Center for Brain, Behaviour and Metabolism, University of Lübeck, Germany
| | - Jules Schneider
- Department of Psychiatry and Psychotherapy, University Hospital Carl Gustav Carus, Technische Universität Dresden, Germany; Department of Neurology, University Hospital Carl Gustav Carus, Technische Universität Dresden, Germany
| | - Frederik D Weber
- Donders Institute for Brain, Cognition and Behaviour, Radboudumc, the Netherlands; Department of Sleep and Cognition, Netherlands Institute for Neuroscience, an institute of the Royal Netherlands Academy of Arts and Sciences, Amsterdam, the Netherlands
| | - Lucia M Talamini
- Department of Psychology, University of Amsterdam, Amsterdam, the Netherlands; Amsterdam Brain and Cognition, University of Amsterdam, Amsterdam, the Netherlands
| | - Martin Dresler
- Donders Institute for Brain, Cognition and Behaviour, Radboudumc, the Netherlands.
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4
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Ngo HVV, Oster H, Andreou C, Obleser J. Circadian rhythms in auditory hallucinations and psychosis. Acta Physiol (Oxf) 2023; 237:e13944. [PMID: 36744985 DOI: 10.1111/apha.13944] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Revised: 01/31/2023] [Accepted: 02/01/2023] [Indexed: 02/07/2023]
Abstract
Circadian rhythms are imprinted in all organisms and influence virtually all aspects of physiology and behavior in adaptation to the 24-h day-night cycle. This recognition of a circadian timekeeping system permeating essentially all healthy functioning of body and mind quickly leads to the realization that, in turn, human ailments should be probed for the degree to which they are rooted in or marked by disruptions and dysregulations of circadian clock functions in the human body. In this review, we will focus on psychosis as a key mental illness and foremost one of its cardinal symptoms: auditory hallucinations. We will discuss recent empirical evidence and conceptual advances probing the potential role of circadian disruption in auditory hallucinations. Moreover, a dysbalance in excitation and inhibition within cortical networks, which in turn drive a disinhibition of dopaminergic signaling, will be highlighted as central physiological mechanism. Finally, we will propose two avenues for experimentally intervening on the circadian influences to potentially alleviate hallucinations in psychotic disorders.
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Affiliation(s)
- Hong-Viet V Ngo
- Department of Psychology, University of Lübeck, Lübeck, Germany
- Center of Brain, Behavior and Metabolism, University of Lübeck, Lübeck, Germany
| | - Henrik Oster
- Center of Brain, Behavior and Metabolism, University of Lübeck, Lübeck, Germany
- Institute of Neurobiology, University of Lübeck, Lübeck, Germany
| | - Christina Andreou
- Center of Brain, Behavior and Metabolism, University of Lübeck, Lübeck, Germany
- Department of Psychiatry and Psychotherapy, University of Lübeck, Lübeck, Germany
| | - Jonas Obleser
- Department of Psychology, University of Lübeck, Lübeck, Germany
- Center of Brain, Behavior and Metabolism, University of Lübeck, Lübeck, Germany
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5
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Ngo HVV, Antony JW, Rasch B. Real-time stimulation during sleep: prior findings, novel developments, and future perspectives. J Sleep Res 2022; 31:e13735. [PMID: 36180062 DOI: 10.1111/jsr.13735] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2022] [Accepted: 09/05/2022] [Indexed: 11/30/2022]
Abstract
Real-time brain stimulation is a powerful technique that continues to gain importance in the field of sleep and cognition. In this special issue, we collected 14 articles about real-time stimulation during sleep, including one review, 12 research articles and one letter covering both human and rodent research from various fields. We hope this special issue sparks greater interest and inspires fellow sleep researchers and clinicians to develop new ideas in the exciting topic of real-time stimulation.
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Affiliation(s)
- Hong-Viet V Ngo
- Department of Psychology, University of Lübeck, Lübeck, Germany.,Center for Brain, Behavior and Metabolism, University of Lübeck, Lübeck, Germany
| | - James W Antony
- Department of Psychology and Child Development, California Polytechnic State University, San Luis Obispo, California, USA
| | - Björn Rasch
- Department of Psychology, University of Fribourg, Fribourg, Switzerland
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Ngo HVV, Born J, Klinzing JG. Protocol for spike-triggered closed-loop auditory stimulation during sleep in patients with epilepsy. STAR Protoc 2022; 3:101505. [PMID: 35942345 PMCID: PMC9356163 DOI: 10.1016/j.xpro.2022.101505] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
Several epilepsies are characterized by interictal spikes in the electroencephalogram occurring preferentially during sleep. We present a closed-loop auditory stimulation protocol with potential for treating sleep epilepsies. We describe the pre-sleep preparations, sleep recordings, the auditory stimulation, in which tones are triggered upon spike detection, and post-sleep procedures. This protocol has been shown to decrease likelihood and amplitude of subsequent spikes in patients with BECTS (Benign epilepsy with centrotemporal spikes) and can be applied to study non-pharmacological treatments of sleep epilepsies. For complete details on the use and execution of this protocol, please refer to Klinzing et al. (2021). Protocol for implementing auditory stimulation in patients with sleep epilepsy Tones are triggered upon detection of a spike Beneficial effects on patients with BECTS epilepsy Potential application as non-pharmacological treatment for sleep epilepsies
Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics.
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7
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Weinhold SL, Lechinger J, Timm N, Hansen A, Ngo HVV, Göder R. Auditory stimulation in-phase with slow oscillations to enhance overnight memory consolidation in patients with schizophrenia? J Sleep Res 2022; 31:e13636. [PMID: 35686351 DOI: 10.1111/jsr.13636] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2021] [Revised: 03/24/2022] [Accepted: 04/27/2022] [Indexed: 11/27/2022]
Abstract
Sleep-dependent memory consolidation is disturbed in patients with schizophrenia, who furthermore show reductions in sleep spindles and probably also in delta power during sleep. The memory dysfunction in these patients is one of the strongest markers for worse long-term functional outcome. However, therapeutic interventions to normalise memory functions, e.g., with medication, still do not exist. Against this backdrop, we investigated to what extent a non-invasive approach enhancing sleep with real-time auditory stimulation in-phase with slow oscillations might affect overnight memory consolidation in patients with schizophrenia. To this end, we examined 18 patients with stably medicated schizophrenia in a double-blinded sham-controlled design. Memory performance was assessed by a verbal (word list) and a non-verbal (complex figure) declarative memory task. In comparison to a sham condition without auditory stimuli, we found that in patients with schizophrenia, auditory stimulation evokes an electrophysiological response similar to that in healthy participants leading to an increase in slow wave and temporally coupled sleep spindle activity during stimulation. Despite this finding, patients did not show any beneficial effect on the overnight change in memory performance by stimulation. Although the stimulation in our study did not improve the patient's memory, the electrophysiological response gives hope that auditory stimulation could enable us to provide better treatment for sleep-related detriments in these patients in the future.
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Affiliation(s)
- Sara Lena Weinhold
- Department of Psychiatry and Psychotherapy (ZIP), University Hospital Schleswig-Holstein (UKSH), Kiel, Germany
| | - Julia Lechinger
- Department of Psychiatry and Psychotherapy (ZIP), University Hospital Schleswig-Holstein (UKSH), Kiel, Germany
| | - Nele Timm
- Department of Psychiatry and Psychotherapy (ZIP), University Hospital Schleswig-Holstein (UKSH), Kiel, Germany
| | - Anja Hansen
- Department of Psychiatry and Psychotherapy (ZIP), University Hospital Schleswig-Holstein (UKSH), Kiel, Germany
| | - Hong-Viet V Ngo
- Department of Psychology, University of Lübeck, Lübeck, Germany
| | - Robert Göder
- Department of Psychiatry and Psychotherapy (ZIP), University Hospital Schleswig-Holstein (UKSH), Kiel, Germany
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8
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Wang JY, Heck KL, Born J, Ngo HVV, Diekelmann S. No difference between slow oscillation up- and down-state cueing for memory consolidation during sleep. J Sleep Res 2022; 31:e13562. [PMID: 35166422 DOI: 10.1111/jsr.13562] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 01/21/2022] [Accepted: 01/25/2022] [Indexed: 11/30/2022]
Abstract
The beneficial effects of sleep for memory consolidation are assumed to rely on the reactivation of memories in conjunction with the coordinated interplay of sleep rhythms like slow oscillations and spindles. Specifically, slow oscillations are assumed to provide the temporal frame for spindles to occur in the slow oscillations up-states, enabling a redistribution of reactivated information within hippocampal-neocortical networks for long-term storage. Memory reactivation can also be triggered externally by presenting learning-associated cues (like odours or sounds) during sleep, but it is presently unclear whether there is an optimal time-window for the presentation of such cues in relation to the phase of the slow oscillations. In the present within-subject comparison, participants (n = 16) learnt word-pairs visually presented with auditory cues of the first syllable. These syllables were subsequently used for real-time cueing either in the up- or down-state of endogenous slow oscillations. Contrary to our hypothesis, we found differences in memory performance neither between up- and down-state cueing, nor between word-pairs that were cued versus uncued. In the up-state cueing condition, higher amounts of rapid eye movement sleep were associated with better memory for cued contents, whereas higher amounts of slow-wave sleep were associated with better memory for uncued contents. Evoked response analyses revealed signs of cue processing in both conditions. Interestingly, both up- and down-state cueing evoked a similar spindle response with the induced slow oscillations up-state at ~1000 ms post-cue. We speculate that our cueing procedure triggered generalised reactivation processes that facilitated the consolidation of both cued and uncued memories irrespective of the slow oscillation phase.
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Affiliation(s)
- Jing-Yi Wang
- Institute of Medical Psychology and Behavioral Neurobiology, University Tübingen, Tübingen, Germany.,State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, Faculty of Psychology at Beijing Normal University, Beijing, China
| | - Katharina L Heck
- Institute of Medical Psychology and Behavioral Neurobiology, University Tübingen, Tübingen, Germany
| | - Jan Born
- Institute of Medical Psychology and Behavioral Neurobiology, University Tübingen, Tübingen, Germany.,Centre for Integrative Neuroscience, University Tübingen, Tübingen, Germany
| | - Hong-Viet V Ngo
- Department of Psychology, University of Lübeck, Lübeck, Germany
| | - Susanne Diekelmann
- Institute of Medical Psychology and Behavioral Neurobiology, University Tübingen, Tübingen, Germany.,Department of Psychiatry and Psychotherapy, University Hospital Tübingen, Tübingen, Germany
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Klinzing JG, Tashiro L, Ruf S, Wolff M, Born J, Ngo HVV. Auditory stimulation during sleep suppresses spike activity in benign epilepsy with centrotemporal spikes. Cell Rep Med 2021; 2:100432. [PMID: 34841286 PMCID: PMC8606903 DOI: 10.1016/j.xcrm.2021.100432] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2020] [Revised: 06/12/2021] [Accepted: 09/27/2021] [Indexed: 11/25/2022]
Abstract
Benign epilepsy with centrotemporal spikes (BECTS) is a common form of childhood epilepsy linked to diverse cognitive abnormalities. The electroencephalogram of patients shows focal interictal epileptic spikes, particularly during non-rapid eye movement (NonREM) sleep. Spike formation involves thalamocortical networks, which also contribute to the generation of sleep slow oscillations (SOs) and spindles. Motivated by evidence that SO-spindle activity can be controlled through closed-loop auditory stimulation, here, we show in seven patients that auditory stimulation also reduces spike rates in BECTS. Stimulation during NonREM sleep decreases spike rates, with most robust reductions when tones are presented 1.5 to 3.5 s after spikes. Stimulation further reduces the amplitude of spikes closely following tones. Sleep spindles are negatively correlated with spike rates, suggesting that tone-evoked spindle activity mediates the spike suppression. We hypothesize spindle-related refractoriness in thalamocortical circuits as a potential mechanism. Our results open an avenue for the non-pharmacological treatment of BECTS. Spikes in BECTS epilepsy and sleep spindles may share thalamocortical generation Auditory stimulation during sleep evokes sleep spindles and suppresses spikes Stimulation may reduce spiking by inducing thalamocortical refractoriness
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Affiliation(s)
- Jens G Klinzing
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, 72076 Tübingen, Germany.,Centre for Integrative Neuroscience, University of Tübingen, 72076 Tübingen, Germany.,Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08540, USA
| | - Lilian Tashiro
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, 72076 Tübingen, Germany
| | - Susanne Ruf
- University Children's Hospital Tübingen, 72076 Tübingen, Germany
| | - Markus Wolff
- Department of Pediatric Neurology, Vivantes Hospital Neukölln, 12351 Berlin, Germany
| | - Jan Born
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, 72076 Tübingen, Germany.,Centre for Integrative Neuroscience, University of Tübingen, 72076 Tübingen, Germany
| | - Hong-Viet V Ngo
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, 72076 Tübingen, Germany.,Department of Psychology, University of Lübeck, 23562 Lübeck, Germany
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10
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Harrington MO, Ashton JE, Ngo HVV, Cairney SA. Phase-locked auditory stimulation of theta oscillations during rapid eye movement sleep. Sleep 2021; 44:5960115. [PMID: 33159523 DOI: 10.1093/sleep/zsaa227] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2020] [Revised: 09/24/2020] [Indexed: 12/15/2022] Open
Abstract
Auditory closed-loop stimulation is a non-invasive technique that has been widely used to augment slow oscillations during non-rapid eye movement sleep. Based on the principles of closed-loop stimulation, we developed a novel protocol for manipulating theta activity (3-7 Hz) in rapid eye movement (REM) sleep. Sixteen healthy young adults were studied in two overnight conditions: Stimulation and Sham. In the Stimulation condition, 1 s of 5 Hz amplitude-modulated white noise was delivered upon detection of two supra-threshold theta cycles throughout REM sleep. In the Sham condition, corresponding time points were marked but no stimulation was delivered. Auditory stimulation entrained EEG activity to 5 Hz and evoked a brief (~0.5 s) increase in theta power. Interestingly, this initial theta surge was immediately followed by a prolonged (~3 s) period of theta suppression. Stimulation also induced a prolonged (~2 s) increase in beta power. Our results provide the first demonstration that the REM sleep theta rhythm can be manipulated in a targeted manner via auditory stimulation. Accordingly, auditory stimulation might offer a fruitful avenue for investigating REM sleep electrophysiology and its relationship to behavior.
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Affiliation(s)
| | | | - Hong-Viet V Ngo
- Donders Institute for Brain, Cognition and Behaviour, Radboudumc, The Netherlands.,Department of Psychology, University of Lübeck, Lübeck, Germany
| | - Scott A Cairney
- Department of Psychology, University of York, Heslington, York, UK.,York Biomedical Research Institute (YBRI), University of York, Heslington, York, UK
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Navarrete M, Schneider J, Ngo HVV, Valderrama M, Casson AJ, Lewis PA. Examining the optimal timing for closed-loop auditory stimulation of slow-wave sleep in young and older adults. Sleep 2021; 43:5686285. [PMID: 31872860 PMCID: PMC7294407 DOI: 10.1093/sleep/zsz315] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2019] [Revised: 12/13/2019] [Indexed: 11/23/2022] Open
Abstract
Study Objectives Closed-loop auditory stimulation (CLAS) is a method for enhancing slow oscillations (SOs) through the presentation of auditory clicks during sleep. CLAS boosts SOs amplitude and sleep spindle power, but the optimal timing for click delivery remains unclear. Here, we determine the optimal time to present auditory clicks to maximize the enhancement of SO amplitude and spindle likelihood. Methods We examined the main factors predicting SO amplitude and sleep spindles in a dataset of 21 young and 17 older subjects. The participants received CLAS during slow-wave-sleep in two experimental conditions: sham and auditory stimulation. Post-stimulus SOs and spindles were evaluated according to the click phase on the SOs and compared between and within conditions. Results We revealed that auditory clicks applied anywhere on the positive portion of the SO increased SO amplitudes and spindle likelihood, although the interval of opportunity was shorter in the older group. For both groups, analyses showed that the optimal timing for click delivery is close to the SO peak phase. Click phase on the SO wave was the main factor determining the impact of auditory stimulation on spindle likelihood for young subjects, whereas for older participants, the temporal lag since the last spindle was a better predictor of spindle likelihood. Conclusions Our data suggest that CLAS can more effectively boost SOs during specific phase windows, and these differ between young and older participants. It is possible that this is due to the fluctuation of sensory inputs modulated by the thalamocortical networks during the SO.
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Affiliation(s)
- Miguel Navarrete
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff, UK
| | - Jules Schneider
- School of Biological Sciences, University of Manchester, Manchester, UK
| | - Hong-Viet V Ngo
- School of Psychology, University of Birmingham, Edgbaston, Birmingham, UK
| | - Mario Valderrama
- Department of Biomedical Engineering, University of Los Andes, Bogotá, Colombia
| | - Alexander J Casson
- School of Electrical and Electronic Engineering, University of Manchester, Manchester, UK
| | - Penelope A Lewis
- Cardiff University Brain Research Imaging Centre (CUBRIC), School of Psychology, Cardiff University, Cardiff, UK
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Schneider J, Lewis PA, Koester D, Born J, Ngo HVV. Susceptibility to auditory closed-loop stimulation of sleep slow oscillations changes with age. Sleep 2021; 43:5850478. [PMID: 32562487 PMCID: PMC7734479 DOI: 10.1093/sleep/zsaa111] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 05/10/2020] [Indexed: 11/20/2022] Open
Abstract
Study Objectives Cortical slow oscillations (SOs) and thalamocortical sleep spindles hallmark slow wave sleep and facilitate memory consolidation, both of which are reduced with age. Experiments utilizing auditory closed-loop stimulation to enhance these oscillations showed great potential in young and older subjects. However, the magnitude of responses has yet to be compared between these age groups. We examined the possibility of enhancing SOs and performance on different memory tasks in a healthy middle-aged population using this stimulation and contrast effects to younger adults. Methods In a within-subject design, 17 subjects (55.7 ± 1.0 years) received auditory stimulation in synchrony with SO up-states, which was compared to a no-stimulation sham condition. Overnight memory consolidation was assessed for declarative word-pairs and procedural finger-tapping skill. Post-sleep encoding capabilities were tested with a picture recognition task. Electrophysiological effects of stimulation were compared to a previous younger cohort (n = 11, 24.2 ± 0.9 years). Results Overnight retention and post-sleep encoding performance of the older cohort revealed no beneficial effect of stimulation, which contrasts with the enhancing effect the same stimulation protocol had in our younger cohort. Auditory stimulation prolonged endogenous SO trains and induced sleep spindles phase-locked to SO up-states in the older population. However, responses were markedly reduced compared to younger subjects. Additionally, the temporal dynamics of stimulation effects on SOs and spindles differed between age groups. Conclusions Our findings suggest that the susceptibility to auditory stimulation during sleep drastically changes with age and reveal the difficulties of translating a functional protocol from younger to older populations.
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Affiliation(s)
- Jules Schneider
- School of Biological Sciences, University of Manchester, Manchester, UK
- School of Psychology, Cardiff University, Cardiff, UK
- Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK
| | - Penelope A Lewis
- School of Biological Sciences, University of Manchester, Manchester, UK
- School of Psychology, Cardiff University, Cardiff, UK
- Corresponding authors. Hong-Viet V. Ngo, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Kapittelweg 29, 6525 EN Nijmegen, The Netherlands. ; Penelope A. Lewis, School of Psychology, Cardiff University, Cardiff, UK.
| | - Dominik Koester
- Institute for Medical Psychology and Behavioural Neurobiology, University of Tübingen, Tübingen, Germany
| | - Jan Born
- Institute for Medical Psychology and Behavioural Neurobiology, University of Tübingen, Tübingen, Germany
- Centre for Integrative Neuroscience, University of Tübingen, Tübingen, Germany
| | - Hong-Viet V Ngo
- Institute for Medical Psychology and Behavioural Neurobiology, University of Tübingen, Tübingen, Germany
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands
- Corresponding authors. Hong-Viet V. Ngo, Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Kapittelweg 29, 6525 EN Nijmegen, The Netherlands. ; Penelope A. Lewis, School of Psychology, Cardiff University, Cardiff, UK.
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Ashton JE, Harrington MO, Langthorne D, Ngo HVV, Cairney SA. Sleep deprivation induces fragmented memory loss. ACTA ACUST UNITED AC 2020; 27:130-135. [PMID: 32179655 PMCID: PMC7079571 DOI: 10.1101/lm.050757.119] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Accepted: 01/03/2020] [Indexed: 01/13/2023]
Abstract
Sleep deprivation increases rates of forgetting in episodic memory. Yet, whether an extended lack of sleep alters the qualitative nature of forgetting is unknown. We compared forgetting of episodic memories across intervals of overnight sleep, daytime wakefulness, and overnight sleep deprivation. Item-level forgetting was amplified across daytime wakefulness and overnight sleep deprivation, as compared to sleep. Importantly, however, overnight sleep deprivation led to a further deficit in associative memory that was not observed after daytime wakefulness. These findings suggest that sleep deprivation induces fragmentation among item memories and their associations, altering the qualitative nature of episodic forgetting.
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Affiliation(s)
- Jennifer E Ashton
- Department of Psychology, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Marcus O Harrington
- Department of Psychology, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Diane Langthorne
- Department of Psychology, University of York, Heslington, York YO10 5DD, United Kingdom
| | - Hong-Viet V Ngo
- Donders Institute for Brain, Cognition, and Behaviour, 6526 HR Nijmegen, The Netherlands
| | - Scott A Cairney
- Department of Psychology, University of York, Heslington, York YO10 5DD, United Kingdom.,York Biomedical Research Institute (YBRI), University of York, Heslington, York YO10 5DD, United Kingdom
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Prehn-Kristensen A, Ngo HVV, Lentfer L, Berghäuser J, Brandes L, Schulze L, Göder R, Mölle M, Baving L. Acoustic closed-loop stimulation during sleep improves consolidation of reward-related memory information in healthy children but not in children with attention-deficit hyperactivity disorder. Sleep 2020; 43:5731400. [DOI: 10.1093/sleep/zsaa017] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2019] [Revised: 01/17/2020] [Indexed: 12/11/2022] Open
Abstract
Abstract
Study Objectives
Slow oscillations (SO) during slow-wave sleep foster the consolidation of declarative memory. Children with attention-deficit hyperactivity disorder (ADHD) display deficits in the sleep-associated consolidation of declarative memory, possibly due to an altered function of SO. The present study aimed at enhancing SO activity using closed-looped acoustic stimulation during slow-wave sleep in children with ADHD.
Methods
A total of 29 male children (14 with ADHD; aged 8–12 years) participated in a double-blind, placebo-controlled study trial. Children spent two experimental nights in a sleep lab, one stimulation night and one sham night. A declarative learning task (word-pair learning) with a reward condition was used as a primary outcome. Secondary outcome variables were a procedural memory (serial reaction time) and working memory (WM; n-back) task. Encoding of declarative and procedural memory took place in the evening before sleep. After sleep, the retrieval took place followed by the n-back task.
Results
The stimulation successfully induced SO activity during sleep in children with and without ADHD. After stimulation, only healthy children performed better on high-rewarded memory items (primary outcome). In contrast, there were indications that only children with ADHD benefitted from the stimulation with respect to procedural as well as WM performance (secondary outcome).
Conclusions
We were able to show that the acoustic closed-loop stimulation can be applied to enhance SO activity in children with and without ADHD. Our data indicate that SO activity during sleep interacts with subsequent memory performance (primary outcome: rewarded declarative memory; secondary outcome: procedural and WM) in children with and without ADHD.
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Affiliation(s)
- Alexander Prehn-Kristensen
- Department of Child and Adolescent Psychiatry and Psychotherapy, Center for Integrative Psychiatry, School of Medicine, Christian-Albrechts-University, Kiel, Germany
| | - Hong-Viet V Ngo
- Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Centre, Nijmegen, The Netherlands
| | - Luisa Lentfer
- Department of Child and Adolescent Psychiatry and Psychotherapy, Center for Integrative Psychiatry, School of Medicine, Christian-Albrechts-University, Kiel, Germany
| | - Julia Berghäuser
- Department of Child and Adolescent Psychiatry and Psychotherapy, Center for Integrative Psychiatry, School of Medicine, Christian-Albrechts-University, Kiel, Germany
- Faculty of Psychology, Technische Universität Dresden, Dresden, Germany
| | - Lena Brandes
- Department of Child and Adolescent Psychiatry and Psychotherapy, Center for Integrative Psychiatry, School of Medicine, Christian-Albrechts-University, Kiel, Germany
| | - Larissa Schulze
- Department of Child and Adolescent Psychiatry and Psychotherapy, Center for Integrative Psychiatry, School of Medicine, Christian-Albrechts-University, Kiel, Germany
| | - Robert Göder
- Department of Psychiatry and Psychotherapy, Center for Integrative Psychiatry, School of Medicine, Christian-Albrechts-University, Kiel, Germany
| | - Matthias Mölle
- Center of Brain, Behavior and Metabolism, University of Lübeck, Lübeck, Germany
| | - Lioba Baving
- Department of Child and Adolescent Psychiatry and Psychotherapy, Center for Integrative Psychiatry, School of Medicine, Christian-Albrechts-University, Kiel, Germany
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Ngo HVV, Seibold M, Boche DC, Mölle M, Born J. Insights on auditory closed-loop stimulation targeting sleep spindles in slow oscillation up-states. J Neurosci Methods 2018; 316:117-124. [PMID: 30194953 DOI: 10.1016/j.jneumeth.2018.09.006] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 08/17/2018] [Accepted: 09/03/2018] [Indexed: 02/04/2023]
Abstract
BACKGROUND The consolidation of sleep-dependent memories is mediated by an interplay of cortical slow oscillations (SOs) and thalamo-cortical sleep spindles. Whereas an enhancement of SOs with auditory closed-loop stimulation has been proven highly successful, the feasibility to induce and boost sleep spindles with auditory stimulation remains unknown thus far. NEW METHOD Here we tested the possibility to enhance spindle activity during endogenous SOs and thereby to promote memory consolidation. Performing a sleep study in healthy humans, we applied an auditory Spindle stimulation and compared it with an Arrhythmic stimulation and a control condition comprising no stimulation (Sham). RESULTS With Spindle stimulation we were not able to directly entrain endogenous spindle activity during SO up-states. Instead, both Spindle and Arrhythmic stimulation evoked a resonant SO response accompanied by an increase in spindle power phase-locked to the SO up-state. Assessment of overnight retention of declarative word-pairs revealed no difference between all conditions. COMPARISON WITH EXISTING METHODS Our Spindle stimulation produced oscillatory evoked responses (i.e., increases in SOs and spindle activity during SO up-states) quite similar to those observed after the auditory closed-loop stimulation of SOs in previous studies, lacking however the beneficial effects on memory retention. CONCLUSION Our findings put the endeavour for a selective enhancement of spindle activity via auditory pathways into perspective and reveal central questions with regard to the stimulation efficacy on both an electrophysiological and a neurobehavioral level.
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Affiliation(s)
- Hong-Viet V Ngo
- School of Psychology, University of Birmingham, Birmingham B15 2TT, United Kingdom; Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen 72076, Germany
| | - Mitja Seibold
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen 72076, Germany
| | - Désirée C Boche
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen 72076, Germany
| | - Matthias Mölle
- Center of Brain, Behavior and Metabolism, University of Lübeck, Lübeck, Germany
| | - Jan Born
- Institute of Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen 72076, Germany; Centre for Integrative Neuroscience, University of Tübingen, Tübingen 72076, Germany.
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Abstract
A region of the brain called the putamen has a central role in procedural memory consolidation during sleep.
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Affiliation(s)
- Hong-Viet V Ngo
- School of Psychology, University of Birmingham, Birmingham, United Kingdom
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Korf EM, Mölle M, Born J, Ngo HVV. Blindfolding during wakefulness causes decrease in sleep slow wave activity. Physiol Rep 2017; 5:5/7/e13239. [PMID: 28408638 PMCID: PMC5392525 DOI: 10.14814/phy2.13239] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2017] [Accepted: 03/13/2017] [Indexed: 12/18/2022] Open
Abstract
Slow wave activity (SWA, 0.5–4 Hz) represents the predominant EEG oscillatory activity during slow wave sleep (SWS). Its amplitude is considered in part a reflection of synaptic potentiation in cortical networks due to encoding of information during prior waking, with higher amplitude indicating stronger potentiation. Previous studies showed that increasing and diminishing specific motor behaviors produced corresponding changes in SWA in the respective motor cortical areas during subsequent SWS. Here, we tested whether this relationship can be generalized to the visual system, that is, whether diminishing encoding of visual information likewise leads to a localized decrease in SWA over the visual cortex. Experiments were performed in healthy men whose eyes on two different days were or were not covered for 10.5 h before bedtime. The subject's EEG was recorded during sleep and, after sleep, visual evoked potentials (VEPs) were recorded. SWA during nonrapid eye movement sleep (NonREM sleep) was lower after blindfolding than after eyes open (P < 0.01). The decrease in SWA that was most consistent during the first 20 min of NonREM sleep, did not remain restricted to visual cortex regions, with changes over frontal and parietal cortical regions being even more pronounced. In the morning after sleep, the N75‐P100 peak‐to‐peak‐amplitude of the VEP was significantly diminished in the blindfolded condition. Our findings confirm a link between reduced wake encoding and diminished SWA during ensuing NonREM sleep, although this link appears not to be restricted to sensory cortical areas.
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Affiliation(s)
| | - Matthias Mölle
- Center of Brain, Behavior and Metabolism University of Lübeck, Lübeck, Germany
| | - Jan Born
- Department of Neuroendocrinology, University of Lübeck, Lübeck, Germany .,Institute for Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen, Germany
| | - Hong-Viet V Ngo
- Institute for Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen, Germany .,School of Psychology University of Birmingham, Birmingham, United Kingdom
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Schellenberger Costa M, Weigenand A, Ngo HVV, Marshall L, Born J, Martinetz T, Claussen JC. A Thalamocortical Neural Mass Model of the EEG during NREM Sleep and Its Response to Auditory Stimulation. PLoS Comput Biol 2016; 12:e1005022. [PMID: 27584827 PMCID: PMC5008627 DOI: 10.1371/journal.pcbi.1005022] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Accepted: 06/17/2016] [Indexed: 11/18/2022] Open
Abstract
Few models exist that accurately reproduce the complex rhythms of the thalamocortical system that are apparent in measured scalp EEG and at the same time, are suitable for large-scale simulations of brain activity. Here, we present a neural mass model of the thalamocortical system during natural non-REM sleep, which is able to generate fast sleep spindles (12–15 Hz), slow oscillations (<1 Hz) and K-complexes, as well as their distinct temporal relations, and response to auditory stimuli. We show that with the inclusion of detailed calcium currents, the thalamic neural mass model is able to generate different firing modes, and validate the model with EEG-data from a recent sleep study in humans, where closed-loop auditory stimulation was applied. The model output relates directly to the EEG, which makes it a useful basis to develop new stimulation protocols. Sleep plays a pivotal role for the consolidation of memory. While REM sleep had originally been the focus of research due to its similarity with wakefulness, more recent studies suggest that different sleep stages are responsible for the consolidation of different types of memory. To better understand the changes in neuronal dynamics between the different sleep stages, neural mass models are a valuable tool, as they relate directly to the large-scale dynamics measured by an EEG. Here, we present a model of the sleeping thalamocortical system. We first show that the isolated thalamic submodule is able to generate different oscillatory behavior found in vivo. Furthermore, the full thalamocortical model reproduces the EEG of sleep stages N2 and N3 and preserves the temporal relationship between cortical K-complexes/slow oscillations and thalamic sleep spindles. A comparison with event related potential data from a recent sleep study in humans demonstrates its possible application in predicting the outcome of external stimulation on EEG rhythms. Our study shows, that a neural mass model incorporating few key mechanisms is sufficient to reproduce the complex brain dynamics observed during sleep.
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Affiliation(s)
- Michael Schellenberger Costa
- Institute for Neuro- and Bioinformatics, University of Lübeck, Lübeck, Germany
- Institute for Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen, Germany
- * E-mail:
| | - Arne Weigenand
- Institute for Neuro- and Bioinformatics, University of Lübeck, Lübeck, Germany
- Graduate School for Computing in Medicine and Life Science, University of Lübeck, Lübeck, Germany
| | - Hong-Viet V. Ngo
- Institute for Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen, Germany
| | - Lisa Marshall
- Graduate School for Computing in Medicine and Life Science, University of Lübeck, Lübeck, Germany
- Institute of Experimental and Clinical Pharmacology and Toxicology, University of Lübeck, Lübeck, Germany
| | - Jan Born
- Institute for Medical Psychology and Behavioral Neurobiology, University of Tübingen, Tübingen, Germany
- Center for Integrative Neuroscience, University of Tübingen, Tübingen, Germany
| | - Thomas Martinetz
- Institute for Neuro- and Bioinformatics, University of Lübeck, Lübeck, Germany
- Graduate School for Computing in Medicine and Life Science, University of Lübeck, Lübeck, Germany
| | - Jens Christian Claussen
- Institute for Neuro- and Bioinformatics, University of Lübeck, Lübeck, Germany
- Computational Systems Biology, Jacobs University Bremen, Bremen, Germany
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Abstract
Brain rhythms regulate information processing in different states to enable learning and memory formation. The <1 Hz sleep slow oscillation hallmarks slow-wave sleep and is critical to memory consolidation. Here we show in sleeping humans that auditory stimulation in phase with the ongoing rhythmic occurrence of slow oscillation up states profoundly enhances the slow oscillation rhythm, phase-coupled spindle activity, and, consequently, the consolidation of declarative memory. Stimulation out of phase with the ongoing slow oscillation rhythm remained ineffective. Closed-loop in-phase stimulation provides a straight-forward tool to enhance sleep rhythms and their functional efficacy.
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Affiliation(s)
- Hong-Viet V Ngo
- Institute of Medical Psychology and Behavioral Neurobiology, and Center for Integrative Neuroscience, University of Tübingen, 72076 Tübingen, Germany
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Abstract
Slow oscillations are electrical potential oscillations with a spectral peak frequency of ∼0.8 Hz, and hallmark the electroencephalogram during slow-wave sleep. Recent studies have indicated a causal contribution of slow oscillations to the consolidation of memories during slow-wave sleep, raising the question to what extent such oscillations can be induced by external stimulation. Here, we examined whether slow oscillations can be effectively induced by rhythmic acoustic stimulation. Human subjects were examined in three conditions: (i) with tones presented at a rate of 0.8 Hz ('0.8-Hz stimulation'); (ii) with tones presented at a random sequence ('random stimulation'); and (iii) with no tones presented in a control condition ('sham'). Stimulation started during wakefulness before sleep and continued for the first ∼90 min of sleep. Compared with the other two conditions, 0.8-Hz stimulation significantly delayed sleep onset. However, once sleep was established, 0.8-Hz stimulation significantly increased and entrained endogenous slow oscillation activity. Sleep after the 90-min period of stimulation did not differ between the conditions. Our data show that rhythmic acoustic stimulation can be used to effectively enhance slow oscillation activity. However, the effect depends on the brain state, requiring the presence of stable non-rapid eye movement sleep.
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Affiliation(s)
- Hong-Viet V Ngo
- Institute for Neuro- and Bioinformatics, University of Lübeck, Germany
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