Oscillatory EEG activity during REM sleep in elderly people predicts subsequent dream recall after awakenings

Several findings underlined that the electrophysiological (EEG) background of the last segment of sleep before awakenings may predict the presence/absence of dream recall (DR) in young subjects. However, little is known about the EEG correlates of DR in elderly people. Only an investigation found differences between recall and non-recall conditions during NREM sleep EEG in older adults, while—surprisingly—no EEG predictor of DR was found for what concerns REMsleep. Considering REMsleep as a privileged scenario to produce mental sleep activity related to cognitive processes, our study aimed to investigate whether specific EEG topography and frequency changes during REM sleep in elderly people may predict a subsequent recall of mental sleep activity. Twenty-one healthy older volunteers (mean age 69.2 ± 6.07 SD) and 20 young adults (mean age 23.4 ± 2.76 SD) were recorded for one night from19 scalp derivations. Dreams were collected upon morning awakenings from REM sleep. EEG signals of the last 5min were analyzed by the Better OSCillation algorithm to detect the peaks of oscillatory activity in both groups. Statistical comparisons revealed that older as well as young individuals recall their dream experience when the last segment of REM sleep is characterized by frontal theta oscillations. No Recall (Recall vs. Non-Recall) × Age (Young vs. Older) interaction was found. This result replicated the previous evidence in healthy young subjects, as shown in within- and between-subjects design. The findings are completely original for older individuals, demonstrating that theta oscillations are crucial for the retrieval of dreaming also in this population. Furthermore, our results did not confirm a greater presence of the theta activity in healthy aging. Conversely, we found a greater amount of rhythmic theta and alpha activity in young than older participants. It is worth noting that the theta oscillations detected are related to cognitive functioning. We emphasize the notion that the oscillatory theta activity should be distinguished from the non-rhythmic theta activity identified in relation to other phenomena such as (a) sleepiness and hypoarousal conditions during the waking state and (b) cortical slowing, considered as an EEG alteration in clinical samples

Cortical electrical activity changes in healthy aging using EEG-eLORETA analysis

Brain aging causes loss of synaptic spines, neuronal apoptosis, and a reduction in neurotransmitter levels. These aging phenomena disturb cortical electrical activity and its synchronization with connected regions. Previous electroencephalography (EEG) studies reported an age-related decrease in electrical activity in the alpha frequency band at occipital, parietal, and temporal areas as well as a decrease in occipital delta activity. However, there is an ongoing debate about whether there is an increase or decrease of the activity in other frequency bands with aging due to inconsistent study findings. In this study, we aimed to detect age-related changes of cortical electrical activities in all five frequency bands (delta, theta, alpha, beta, and gamma) in a large sample of healthy subjects for the first time. Using eLORETA (exact low-resolution brain electromagnetic tomography) analysis, we applied an eLORETA source estimation method to resting-state EEG data in 147 healthy subjects (median age 55, IQR 26.5–67.0) to obtain cortical electrical activity and assessed age-related changes in this activity using correlation analysis with multiple comparison correction. The combination of the eLORETA source estimation method and correlation analysis implemented in eLORETA software detected age-related changes in specific cortical regions for each frequency band: (1) delta and theta cortical electrical activities decreased at the occipital area with age, (2) alpha cortical electrical activity decreased at the occipitoparietotemporal areas with age, (3) beta cortical electrical activity increased at the insula, sensorimotor area, supplementary motor area, premotor area, and right temporal areas with age (most significant correlation at the right insula), (4) gamma cortical electrical activity increased at the frontoparietal and left temporal areas with age. These findings extend previous EEG study findings and provide valuable information related to mechanisms of healthy aging. Overall, our findings revealed that even healthy aging greatly affects cortical electrical activities in a region-specific way

Alterations in rhythmic and non-rhythmic resting-state EEG activity and their link to cognition in older age

While many structural and biochemical changes in the brain have been previously associated with aging, the findings concerning electrophysiological signatures, reflecting functional properties of neuronal networks, remain rather controversial. To try resolve this issue, we took advantage of a large population study (N=1703) and comprehensively investigated the association of multiple EEG biomarkers (power of alpha and theta oscillations, individual alpha peak frequency (IAF), the slope of 1/f power spectral decay), aging, and aging and cognitive performance. Cognitive performance was captured with three factors representing processing speed, episodic memory, and interference resolution. Our results show that not only did IAF decline with age but it was also associated with interference resolution over multiple cortical areas. To a weaker extent, 1/f slope of the PSD showed age-related reductions, mostly in frontal brain regions. Finally, alpha power was negatively associated with the speed of processing in the right frontal lobe, despite the absence of age-related alterations. Our results thus demonstrate that multiple electrophysiological features, as well as their interplay, should be considered when investigating the association between age, neuronal activity, and cognitive performance

Trouble comportemental en sommeil paradoxal idiopathique et synucleinopathies : rythmes spectraux et connectivité fonctionnelle à l’EEG au repos

Le trouble comportemental en sommeil paradoxal idiopathique (TCSPi) précède de plusieurs années le diagnostic d’une maladie synucléinopathique. Dans cette étude, nous cherchions à déterminer si la puissance spectrale relative, les composantes rythmiques et arythmiques des spectres de puissance, ainsi que la connectivité fonctionnelle permettaient d’identifier à un temps de base les patients ayant un TCSPi qui développerait une synucléinopathie lors des suivis cliniques annuels. Un enregistrement EEG au repos et une évaluation neuropsychologique ont été conduits auprès de quatre-vingt-un participants atteints d’un TCSPi (66.89 ± 6.91 ans, 20 femmes) et des évaluations neurologiques annuelles étaient menées afin de définir si les patients montraient des symptômes d’une maladie synucléinopathique. La puissance spectrale standard ainsi qu’une estimation spectrale des composantes rythmiques et arythmiques ont été calculées. Ensuite, la connectivité fonctionnelle globale et entre chaque paire d’électrodes ont été estimée par le weighted Phase Lag Index. Après une durée de suivi de 5.01 ± 2.76 ans, 34 participants ont été diagnostiqués avec une synucléinopathie et 47 sont restés exempts de maladie. Comparativement aux participants avec un TCSPi n’ayant pas converti, ceux ayant converti montraient, lors de l’évaluation de base, une puissance spectrale relative plus élevée dans la bande thêta, une pente de la composante arythmique plus abrupte ainsi qu'une puissance rythmique plus élevée en thêta dans les régions occipitales et temporales ainsi qu’en en bêta1 dans les régions frontales. De plus, les patients TCSPi ayant converti présentaient une hyperconnectivité globale dans la bande bêta, mais une hypoconnectivité dans la bande alpha entre les régions temporo-occipitales gauches lors de l’évaluation de base comparativement à ceux n’ayant pas converti. Les altérations mesurables en EEG au repos lors de l’évaluation de base chez les participants avec TCSPi ayant converti vers une maladie synucléinopathique suggèrent une perturbation des réseaux à grande échelle affectés par la neurodégénérescence précoce des structures sous-corticales.Idiopathic REM sleep behavior disorder (iRBD) precedes the diagnosis of synucleinopathies by several years. In this study, we aimed to determine whether relative spectral power, rhythmic and arrhythmic components of power spectra, and functional connectivity at baseline could identify patients with iRBD who will develop a synucleinopathy at follow-up. Resting-state EEG recordings and neuropsychological evaluations were conducted on eighty-one participants with iRBD (66.89 ± 6.91 years; 20 women), and annual neurological assessments were performed to define the emergence of synucleinopathy symptoms. Standard spectral power and spectral estimates of rhythmic and arrhythmic components were calculated. Additionally, global and pairwise functional connectivity were estimated using the weighted Phase Lag Index. After a follow-up period of 5.01 ± 2.76 years, 34 participants were diagnosed with a synucleinopathic disorder, while 47 remained disease-free. Compared to patients who did not convert, patients who converted at follow-up exhibited higher relative spectral power in the theta band, steeper slopes of the arrhythmic component, and increased rhythmic power in theta in posterior regions and beta1 in frontal regions at baseline evaluation. Furthermore, participants who converted showed hyperconnectivity in the beta band and hypoconnectivity in the alpha band between left temporo-occipital regions at baseline compared to participants who did not convert. The measurable alterations in resting-state EEG at baseline in participants with iRBD who phenoconverted towards a synucleinopathy suggest disruption of large-scale networks affected by early neurodegeneration of subcortical structures

Cognitive aging at work and in daily life—a narrative review on challenges due to age-related changes in central cognitive functions

Demographic change is leading to an increasing proportion of older employees in the labor market. At the same time, work activities are becoming more and more complex and require a high degree of flexibility, adaptability, and cognitive performance. Cognitive control mechanism, which is subject to age-related changes and is important in numerous everyday and work activities, plays a special role. Executive functions with its core functions updating, shifting, and inhibition comprises cognitive control mechanisms that serve to plan, coordinate, and achieve higher-level goals especially in inexperienced and conflicting actions. In this review, influences of age-related changes in cognitive control are demonstrated with reference to work and real-life activities, in which the selection of an information or response in the presence of competing but task-irrelevant stimuli or responses is particularly required. These activities comprise the understanding of spoken language under difficult listening conditions, dual-task walking, car driving in critical traffic situations, and coping with work interruptions. Mechanisms for compensating age-related limitations in cognitive control and their neurophysiological correlates are discussed with a focus on EEG measures. The examples illustrate how to access influences of age and cognitive control on and in everyday and work activities, focusing on its functional role for the work ability and well-being of older people

Measures of Resting State EEG Rhythms for Clinical Trials in Alzheimer’s Disease:Recommendations of an Expert Panel

The Electrophysiology Professional Interest Area (EPIA) and Global Brain Consortium endorsed recommendations on candidate electroencephalography (EEG) measures for Alzheimer's disease (AD) clinical trials. The Panel reviewed the field literature. As most consistent findings, AD patients with mild cognitive impairment and dementia showed abnormalities in peak frequency, power, and "interrelatedness" at posterior alpha (8-12Hz) and widespread delta (<4Hz) and theta (4-8Hz) rhythms in relation to disease progression and interventions. The following consensus statements were subscribed: (1) Standardization of instructions to patients, resting state EEG (rsEEG) recording methods, and selection of artifact-free rsEEG periods are needed; (2) power density and "interrelatedness" rsEEG measures (e.g., directed transfer function, phase lag index, linear lagged connectivity, etc.) at delta, theta, and alpha frequency bands may be use for stratification of AD patients and monitoring of disease progression and intervention; and (3) international multisectoral initiatives are mandatory for regulatory purposes

Measures of resting state EEG rhythms for clinical trials in alzheimer's disease patients : recommendations of an expert panel

Background and Aim: Eyes-closed resting state electroencephalographic (rsEEG) rhythms reflect neurophysiological oscillatory mechanisms of synchronization/desynchronization of activity within neural populations of ascending reticular activating brain systems and thalamus-cortical circuits involved in quite vigilance regulation. Currently, they are not considered as biomarkers of Alzheimer’s disease (AD) in the amyloid, tau and neurodegeneration (ATN) Framework of Alzheimer’s Association and National Institute of Aging (AA-NIA). The Electrophysiology Professional Interest Area (EPIA) of AA and Global Brain Consortium endorsed this article written by a multidisciplinary Expert Panel to provide recommendations on candidate rsEEG measures for AD clinical trials. Method: The Panel revised the field literature and reached consensus about the rsEEG measures consistently associated with clinical phenotypes and neuroimaging markers of AD in previous international multicentric clinical trials. Most consistent findings: AD patients with mild cognitive impairment and dementia displayed reduced peak frequency, power, and paired-electrode “interrelatedness” in posterior alpha (8-12 Hz) rhythms and topographically widespread increases in delta (< 4 Hz) and theta (4-8 Hz) rhythms. Recommendations: (i) Careful multi-center standardization of instructions to patients, rsEEG recordings, and selection of artifact-free rsEEG periods; (ii) extraction of rsEEG power density and paired-electrode “interrelatedness” (e.g., directed transfer function, phase lag index, linear lagged connectivity, etc.) rsEEG measures computed at delta, theta, and alpha frequency bands by validated open-access software platforms for replicability; (iii) valid use of those measures in stratification of AD patients and monitoring of disease progression and intervention; and iv) international initiatives to cross-validate rsEEG measures (including nonlinear) for disease monitoring and intervention

Neurobiologia del ricordo onirico: la ricerca delle basi elettrofisiologiche del richiamo e dell'oblio del sogno

Negli ultimi anni numerosi studi hanno tentato di indagare i correlati EEG alla base del richiamo del sogno, partendo dall’assunzione che il ricordo onirico sia l’unico e possibile oggetto di indagine scientifica. Marzano et al. (2011) hanno osservato che specifici pattern EEG presenti negli ultimi 5 minuti di sonno erano in grado di predire il successivo recupero del sogno. Nello specifico, il decremento dell’alpha temporo-parietale durante lo stadio 2 NREM e l’incremento del theta frontale durante il REM erano associati al ricordo onirico. Dal momento che tali pattern EEG erano già stati riscontrati in veglia in relazione a buone prestazioni in compiti di memoria episodica (Klimesch, 1996; 1999), fu possibile ipotizzare una sovrapponibilità tra i meccanismi di codifica e recupero delle memorie episodiche tra diversi stati di coscienza. Nonostante la ricerca delle basi EEG del richiamo del sogno abbia fatto notevoli passi in avanti negli ultimi decenni, rimangono ancora irrisolte alcune questioni. Da una parte, si deve considerare che la maggior parte delle indagini sono state condotte mediante disegni between-subjects, non consentendo di comprendere se i pattern EEG relati al ricordo onirico fossero ascrivibili a fattori di stato o di tratto. Dall’altra parte, si vuole sottolineare che gli studi sono stati realizzati quasi esclusivamente su soggetti giovani e la relazione tra invecchiamento e dreaming è stata scarsamente indagata. L’obiettivo del primo lavoro è stato proprio quello di chiarire la questione “stato-tratto” mediante un disegno within-subjects, tentando, dunque, di comprendere se i correlati EEG del ricordo onirico fossero dipendenti da fattori contingenti il background fisiologico di riferimento da cui i soggetti venivano risvegliati (ipotesi di stato), oppure se fossero dipendenti da fattori interindividuali stabili dei soggetti registrati (ipotesi di tratto). 24 soggetti giovani sono stati registrati mediante polisonnografia (PSG) per almeno 2 sessioni sperimentali, al fine di ottenere entrambe le condizioni di ricordo (REC) e non-ricordo (NREC) del sogno al risveglio da uno stesso stadio di sonno (2NREM o REM). I dati quantitativi dell’EEG sono stati analizzati con la Fast Fourier Transform. I confronti statistici tra REC e NREC hanno mostrato che: a) il ricordo onirico al risveglio da NREM è predetto da un decremento del delta fronto-temporale sinistro (p≤0.0034).; b) il ricordo onirico al risveglio da REM è associato all’incremento dell’alpha parietale (p≤0.008) e da un trend che va nella direzione di un incremento del theta frontale. Date le numerose evidenze di una relazione tra theta frontale e memoria, si è scelto di applicare un’analisi specifica per l’attività oscillatoria (algoritmo BOSC-Better OSCillation, Caplan et al., 2001) del range del theta, che ha confermato la presenza di una robusta associazione tra il theta delle regioni frontopolari e il ricordo onirico. Tale pattern EEG è risultato, peraltro, relato al carico emotivo soggettivamente stimato del ricordo del sogno. Tali risultati sono da un lato in linea con i Modelli di Attivazione (Antrobus, 1991), vale a dire con l’idea che un background EEG caratterizzato da una maggiore desincronizzazione possa favorire il successivo recupero dell’attività mentale (Antrobus, 1991). Dall’altro, la relazione tra il theta frontale e il ricordo onirico nel REM replica i riscontri di Marzano et al. (2011), fornendo ulteriore supporto all’ipotesi di continuità. Inoltre, i risultati sono coerenti con una ipotesi di “stato”: non sono caratteristiche stabili dei soggetti registrati a predire il ricordo onirico al risveglio, ma è una particolare attività corticale durante uno specifico stadio di sonno a determinare il successivo richiamo del sogno. Il secondo studio aveva lo scopo di indagare gli specifici pattern EEG relati al ricordo onirico nell’anziano. 40 anziani sani sono stati registrati con PSG notturna. 20 soggetti sono stati risvegliati da fase REM e 20 da stadio 2 NREM, raccogliendo al mattino l’eventuale ricordo onirico. I dati quantitativi dell’EEG sono stati analizzati con la Fast Fourier Transform. Per gli ultimi 5 min di sonno è stata effettuata la detezione dell’attività oscillatoria con il metodo BOSC. I confronti statistici tra i REC e i NREC hanno evidenziato che: a) Il ricordo onirico al risveglio da stadio 2 è associato ad una trend che va nella direzione di un incremento dell’attività beta nelle aree temporali durante l’intera notte; b) Il ricordo onirico al risveglio da REM è associato ad un trend che va nella direzione di un incremento dell’attività alpha durante l’intera notte. La BOSC ha rilevato che le oscillazioni alpha a 8.5 Hz negli ultimi minuti di sonno REM predicono il successivo ricordo onirico (p≤0.025). E’ emersa inoltre una relazione robusta tra alcuni parametri macrostrutturali, indicativi della frammentarietà del sonno, e le variabili oniriche. In particolare, per i soggetti risvegliati da sonno NREM: a) la vividezza del ricordo onirico è correlata positivamente alla durata della veglia intrasonno; b) l’indice di efficienza del sonno è correlato negativamente alla lunghezza soggettivamente stimata del sogno; c) il numero totale di parole del report è correlato negativamente al numero di arousal. Per i soggetti risvegliati da sonno REM la bizzarria è correlata positivamente con il numero di arousal. Presi assieme, tali risultati appaiano compatibili con quanto rilevato nello studio precedente, e, dunque, ancora una volta in linea con i Modelli di Attivazione (Antrobus, 1991), dal momento che l’elevata attività beta in NREM e l'attività alpha in REM possono ritenersi espressione di un relativo arousal corticale. E’ opportuno evidenziare alcuni limiti presenti nei due studi condotti. Nel primo esperimento, sebbene i nap pomeridiani abbiano consentito di reiterare più agevolmente le sessioni sperimentali, è possibile che il sonno dei soggetti registrati possa essere meno stabile in questa fascia oraria. Nel secondo lavoro emerge, invece, l’assenza di una notte di adattamento. Tale scelta è stata motivata da una difficoltà di reclutamento e disponibilità, entro la popolazione anziana, di modificare le proprie abitudini di sonno per più di una notte consecutiva. Sarebbe opportuno per il futuro realizzare un’indagine volta a confrontare i correlati EEG del ricordo onirico tra giovani ed anziani entro un unico protocollo notturno. Inoltre, sarà utile considerare anche la condizione del “white dream”, corrispondente alla sensazione del soggetto di aver sognato senza però essere in grado di riportare alcun contenuto onirico. E’, infatti, possibile ipotizzare che a un livello “intermedio” di ricordo onirico, possa corrispondere anche un livello medio di attivazione corticale. Infine, si prevede di tenere sotto controllo, con ulteriori indagini, il contributo della variabile omeostatica e circadiana, implementando un protocollo notturno che preveda risvegli multipli per ciascuno stadio e ciclo di sonno, con la relativa raccolta di report onirici

Phase-Amplitude Coupling of Theta and Gamma Rhythms During Rapid Eye Movement Sleep Impacting Memory Across the Lifespan

Phase-amplitude coupling (PAC) between brain oscillations is thought to be an underlying neural mechanism of memory consolidation. Oscillation coupling may become weaker with greater age, possibly explaining natural memory decline across the lifespan, as suggested by studies of PAC during non-rapid-eye-movement sleep. Theta-gamma PAC (TGC) during wake is correlated with stronger encoding and better recall. However, it is unclear how TGC during rapid-eye-movement (REM) sleep correlates with memory or changes with age. I aimed to find TGC during REM sleep (REM TGC) affecting sleep-dependent memory consolidation that changes with age-related memory decline. We recorded scalp electroencephalography of good sleeping younger and older adults. Oscillatory data was extracted from filtered electroencephalography signals. Before sleep, participants learned a declarative memory or non-memory control task, then retested the respective task after sleep to measure memory consolidation. Memory consolidation was better in younger, compared to older, adults. REM TGC strength, measured by a modulation index, was not different between age groups nor task nights. Faster gamma coupling in a frontal channel was positively correlated with and predicts improvements in memory consolidation in younger adults. Slower gamma coupling in a central channel was positively correlated with memory consolidation in older adults. Our results suggest REM TGC strength is stable across the lifespan. However, the strength of faster TGC in younger and of slower TGC in older adults may improve memory consolidation. These results uncover more about how REM sleep and REM TGC changes across the lifespan, in relation to memory. Keywords: rapid eye movement sleep, theta-gamma phase-amplitude coupling, sleep-dependent memory consolidation, agin