Il Sonniloquio come via d’accesso all’elaborazione cognitiva in sonno: uno studio elettrofisiologico sulle produzioni verbali notturne

INTRODUCTION Sleep Talking (ST) is defined as the utterance of speech during sleep. The available literature cannot address ST as a REM or NREM parasomnias. Rarely studied as an isolated phenomenon, we currently have no definite evidence of its neural correlates. Recently, psycholinguistic features of verbal production in ST has been investigated, pointing to coherence with formal features of the language in wakefulness. This evidence, within the hypothesis of an involvement of parasomnias in sleep-related cognitive processing, suggests the importance of understanding the neural mechanism underlying ST. We aimed to investigate EEG correlates predictive of verbal activation (Verbal ST), with a comparison with Non-verbal ST (moaning, laughing, crying, etc…) with the general hypothesis of shared mechanisms with neural correlates of language processing and production. METHOD Six highly frequent ST (3M, 3F, age 19-27, mean 23.83±3.60) recruited through an online survey (general health assessment, PSQI for the self-declared quality of sleep, MUPS for self-declared presence and frequency of the phenomenon). Presence and frequency of ST, together with the compliance in maintaining a regular sleep schedule, has been further assessed through one week of home sleep/dream-logs and audio-activated recorder. The suitable participants have been recorded in the laboratory for at least 2-consecutive nights of video-PSG. We pursued the conditions of Verbal and Non-verbal ST, obtaining a total of 21 Verbal ST and 21 Non-verbal ST in Stage 2 NREM. Control comparison has been performed between Vocalizations (N=42 vocal activations, combining Verbal and Non-verbal) and Baseline (N=42 equivalent sleep interval, 2 mins preceding each ST), to assess time-locking and specificity of the observed EEG pattern, in relation with vocal production. Artifacts were off-line rejected for the 20 seconds EEG preceding each Verbal and Non-verbal ST and Baseline, on a 4-seconds basis. EEG power spectra have been obtained throughout a Fast Fourier Transform (FFT) routine. The power spectra have been then averaged to obtain the canonical sleep EEG bands: delta (0.5-4.5Hz), theta (4.75-7.75Hz), alpha (8-11.75Hz), sigma (12-15.75Hz) and beta (16-24.75Hz), and subsequently log-transformed. RESULTS Statistical comparisons (t-Test) show a general decrement in power spectra for Verbal ST vs. Non-verbal ST for the theta and alpha EEG bands. This effect is strongly lateralized to the left hemisphere and specifically localized on centro-parietal-occipitals channels. A single left parietal channel (P7; theta t=-4.48, p=0.0002; alpha t=-3.29, p=0.0037) was significant also after the Bonferroni correction. T-test comparisons (t=≥2.96; p≤0.0051) for Vocalizations vs. Baseline show a general increment in power spectra for delta on frontal, central and temporal channels, almost on the entire scalp for the alpha band; on Fc2 and C4 for the beta band. CONCLUSIONS Our results suggest shared neural mechanisms between Verbal ST and language programming during wakefulness. Specifically, the selective decrement for the theta band on the left parietal sites is coherent with the literature about linguistic planning in wakefulness, suggesting a possible functional overlapping. Moreover, the phenomenon seems time-locked to the interval of sleep preceding ST, as demonstrated throughout a comparison with a preceding sleep interval

Spotlight on dream recall. The ages of dreams

Brain and sleep maturation covary across different stages of life. At the same time, dream generation and dream recall are intrinsically dependent on the development of neural systems. The aim of this paper is to review the existing studies about dreaming in infancy, adulthood, and the elderly stage of life, assessing whether dream mentation may reflect changes of the underlying cerebral activity and cognitive processes. It should be mentioned that some evidence from childhood investigations, albeit still weak and contrasting, revealed a certain correlation between cognitive skills and specific features of dream reports. In this respect, infantile amnesia, confabulatory reports, dream-reality discerning, and limitation in language production and emotional comprehension should be considered as important confounding factors. Differently, growing evidence in adults suggests that the neurophysiological mechanisms underlying the encoding and retrieval of episodic memories may remain the same across different states of consciousness. More directly, some studies on adults point to shared neural mechanisms between waking cognition and corresponding dream features. A general decline in the dream recall frequency is commonly reported in the elderly, and it is explained in terms of a diminished interest in dreaming and in its emotional salience. Although empirical evidence is not yet available, an alternative hypothesis associates this reduction to an age-related cognitive decline. The state of the art of the existing knowledge is partially due to the variety of methods used to investigate dream experience. Very few studies in elderly and no investigations in childhood have been performed to understand whether dream recall is related to specific electrophysiological pattern at different ages. Most of all, the lack of longitudinal psychophysiological studies seems to be the main issue. As a main message, we suggest that future longitudinal studies should collect dream reports upon awakening from different sleep states and include neurobiological measures with cognitive performance

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

In search of sleep biomarkers of Alzheimer's disease: K-Complexes do not discriminate between patients with mild cognitive impairment and healthy controls

The K-complex (KC) is one of the hallmarks of Non-Rapid Eye Movement (NREM) sleep. Recent observations point to a drastic decrease of spontaneous KCs in Alzheimer's disease (AD). However, no study has investigated when, in the development of AD, this phenomenon starts. The assessment of KC density in mild cognitive impairment (MCI), a clinical condition considered a possible transitional stage between normal cognitive function and probable AD, is still lacking. The aim of the present study was to compare KC density in AD/ MCI patients and healthy controls (HCs), also assessing the relationship between KC density and cognitive decline. Twenty amnesic MCI patients underwent a polysomnographic recording of a nocturnal sleep. Their data were compared to those of previously recorded 20 HCs and 20 AD patients. KCs during stage 2 NREM sleep were visually identified and KC densities of the three groups were compared. AD patients showed a significant KC density decrease compared with MCI patients and HCs, while no differences were observed between MCI patients and HCs. KC density was positively correlated with Mini-Mental State Examination (MMSE) scores. Our results point to the existence of an alteration of KC density only in a full-blown phase of AD, which was not observable in the early stage of the pathology (MCI), but linked with cognitive deterioratio

Pandemic nightmares: effects on dream activity of the COVID-19 lockdown in Italy

COVID-19 has critically impacted the world. Recent works have found substantial changes in sleep and mental health during the COVID-19 pandemic. Dreams could give us crucial information about people's well-being, so here we have directly investigated the consequences of lockdown on the oneiric activity in a large Italian sample: 5,988 adults completed a web-survey during lockdown. We investigated sociodemographic and COVID-19-related information, sleep quality (by the Medical Outcomes Study-Sleep Scale), mental health (by the Depression, Anxiety, and Stress Scales), dream and nightmare frequency, and related emotional aspects (by the Mannheim Dream Questionnaire). Comparisons between our sample and a population-based sample revealed that Italians are having more frequent nightmares and dreams during the pandemic. A multiple logistic regression model showed the predictors of high dream recall (young age, female gender, not having children, sleep duration) and high nightmare frequency (young age, female gender, modification of napping, sleep duration, intrasleep wakefulness, sleep problem index, anxiety, depression). Moreover, we found higher emotional features of dream activity in workers who have stopped working, in people who have relatives/friends infected by or who have died from COVID-19 and in subjects who have changed their sleep habits. Our findings point to the fact that the predictors of high dream recall and nightmares are consistent with the continuity between sleep mentation and daily experiences. According to the arousal-retrieval model, we found that poor sleep predicts a high nightmare frequency. We suggest monitoring dream changes during the epidemic, and also considering the implications for clinical treatment and prevention of mental and sleep disorders

History of Dreaming

In the late 1920s, the psychiatrist Hans Berger introduced a new technique to detect the cortical activity from the scalp of human being. In 1929, the physician showed the first registration of the cortical electric activity obtained by means of electroencephalography machine, from which it was possible to get an electroencephalogram (EEG) on printed paper. In subsequent years, such technique was also adopted for sleep recordings (Loomis et al., 1937), revealing that the electric activity was not homogeneous, but instead, it changed across each night. For several decades, ocular movements observed during sleep were considered casual and insignificant. However, Eugene Aserinsky, a physiology student at the University of Chicago under the supervision of Nathaniel Kleitman, revolutionized sleep scientific research by measuring cerebral activity and ocular movements simultaneously through electrooculography (EOG). They discovered specific intervals with rapid and recurrent eye movement and burst of alpha activity, comparable to those during wakefulness (Aserinsky e Kleitman, 1953). They named this particular kind of sleep as Rapid Eye Movement (REM), which for its features (i.e., desynchronized EEG activity, muscular atonia and rapid eye movements) is also known as "paradoxical sleep". On the other hand, the Non-Rapid Eye Movement (NREM) sleep consists of 1 and 2 lighter sleep stages and 3 and 4 deeper sleep stages and exhibits slow and synchronized EEG activity. Essentially, the year 1953 coincides with the birth of psychophysiology of sleep. Until then, psychoanalysis had the primacy in the study of dreams. Freudian theories about their interpretation considered the oneiric activity as a doorway to access the unconscious functions of mind in the neurosis care (Freud, 1899). From 1953, the enthusiasm for the discovery of REM sleep considerably influenced the following research about dreaming: it was developed the idea that the specific physiology of REM sleep would generate oneiric activity, since it was being observed the highest probability to find the dream recall at awake from this stage. IndeedAserinsky e Kleitman (1953b) , in their first studies, found dream reports with hallucinatory, complex and bizarre content in 74% of awakes from REM sleep. On the contrary, the same results were found only in 9% of awakenings from NREM sleep (Eiser, 2005), in which mental activity with poor mental images was more frequent, without structured plot or, in some cases, the impossibility to recall the dream (Horne, 1993). For several years thereafter, almost the totality of studies was set up on the biunivocal correspondence REM=dreaming (Hobson & McCarley, 1977; Hobson, 1988; Maquet et al., 1996; Braun et al., 1997; Nofzinger et al., 1997; Hobson et al., 2000). In fact, because of the specific physiological differences between sleep stages, many researchers considered REM sleep as the neural correlate of dreaming. Researchers asked the subjects if they were dreaming something before awakening, influencing in this way the answer. Indeed, any individual could give a different subjective interpretation to the word "dream". Bearing in mind this consideration, in 1962 the psychologist David Foulkes realized that it was possible to obtain oneiric report also after awakenings from NREM sleep, just modifying the question and using more liberal criteria. More generally, Foulkes asked the participants if “anything passing through your mind” (Foulkes, 1962; Horne, 1993). After several in-depth analyses in this direction, two fundamental studies questioned correspondence REM=dreaming. Antrobus (1983) and Foulkes & Schmidt (1983) reported that sleep mentation occurred for the whole night, without any qualitative or quantitative difference between REM and NREM sleep. Indeed, dreams occurred in any sleep stage, during the slow wave activity and the sleep onset or the relaxed wakefulness (e.g., hypnagogic and hypnopompic hallucinations; Cavallero, 2000) and, sometimes, they could be longer in NREM than in REM sleep (Foulkes & Schmidt, 1983; Cavallero et al., 1990). Currently, the correspondence REM sleep=dreaming is still present, but it is transformed in a long debate about different mechanisms of dream's generation (Nielsen, 2000). According to many neuropsychological, neuroimaging and EEG studies, it can be now stated that mental activity occurs for the entire period of sleep (Foulkes, 1962; 1967), although with some differences which concern dream-like features (many characters, vivid images, structured and bizarre plot), on one side, (Foulkes & Rechtschaffen, 1964; Foulkes, 1967; Foulkes & Schmidt, 1983; Antrobus, 1983; Casagrande, Violani & Bertini, 1996; Stickgold, Pace-Scott & Hobson, 1994; Waterman, Elton & Kenemans, 1993) and thought-like features (vague and few images; Foulkes, 1967), on the other. In this contest, some researchers hypothesized that dreams produced from REM sleep would be more dream-like and that dreams generated from NREM sleep would be more thought-like and proposed the so-called Two-Generation Model (2-gen model; Hobson, Pace-Scott & Stickgold, 2000; Nielsen, 2000). Nevertheless, this hypothesis was not ever being demonstrated (Antrobus, 1983; Bartolacci, Scarpelli & De Gennaro, 2017). Indeed, many vivid and hallucinatory dreams also occur in NREM sleep, as pavor nocturnus from stages 3 and 4 (Nielsen, 2000; Fisher et al., 1970a; 1970b; 1973; Kahan, Fisher & Edwards, 1991) or hypnagogic and hypnopompic hallucinations in transient states sleep-wakefulness (Nielsen, 2017). For these reasons, assuming the homogeneity of mental activity during the sleep, the One-Generation Model has been proposed (1-gen model; Solms, 2000; Foulkes, 1962; 1967), that will be discussed more in detail below

Sleep talking:.A viable access to mental processes during sleep

SUMMARY: Sleep talking is one of the most common altered nocturnal behaviours in the whole population. It does not represent a pathological condition and consists in the unaware production of vocalisations during sleep. Although in the last few decades we have experienced a remarkable increase in knowledge about cognitive processes and behavioural manifestations during sleep, the literature regarding sleep talking remains dated and fragmentary. We first provide an overview of historical and recent findings regarding sleep talking, and we then discuss the phenomenon in the context of mental activity during sleep. It is shown that verbal utterances, reflecting the ongoing dream content, may represent the unique possibility to access the dreamlike mental experience directly. Furthermore, we discuss such phenomena within a cognitive theoretical framework, considering both the atypical activation of psycholinguistic circuits during sleep and the implications of verbal ‘replay’ of recent learning in memory consolidation. Despite current knowledge on such a common experience being far from complete, an in-depth analysis of sleep talking episodes could offer interesting opportunities to address fundamental questions on dreaming or information processing during sleep. Further systematic polysomnographic and neuroimaging investigations are expected to shed new light on the manifestation of the phenomenon and related aspect

Sleep talking:.A viable access to mental processes during sleep

SUMMARY: Sleep talking is one of the most common altered nocturnal behaviours in the whole population. It does not represent a pathological condition and consists in the unaware production of vocalisations during sleep. Although in the last few decades we have experienced a remarkable increase in knowledge about cognitive processes and behavioural manifestations during sleep, the literature regarding sleep talking remains dated and fragmentary. We first provide an overview of historical and recent findings regarding sleep talking, and we then discuss the phenomenon in the context of mental activity during sleep. It is shown that verbal utterances, reflecting the ongoing dream content, may represent the unique possibility to access the dreamlike mental experience directly. Furthermore, we discuss such phenomena within a cognitive theoretical framework, considering both the atypical activation of psycholinguistic circuits during sleep and the implications of verbal ‘replay’ of recent learning in memory consolidation. Despite current knowledge on such a common experience being far from complete, an in-depth analysis of sleep talking episodes could offer interesting opportunities to address fundamental questions on dreaming or information processing during sleep. Further systematic polysomnographic and neuroimaging investigations are expected to shed new light on the manifestation of the phenomenon and related aspect

Spatiotemporal dynamics of sleep spindle sources across NREM Sleep Cycles

The existence of two different types of sleep spindles (slow and fast) is well-established, according to their topographical distribution at scalp- and cortical-level. Our aim was to provide a systematic investigation focused on the temporal evolution of sleep spindle sources during non-rapid eye movement (NREM) sleep. Spindle activity was recorded and automatically detected in 20 healthy subjects. Low resolution brain electromagnetic tomography (LORETA) was applied for the EEG source localization. Aiming to evaluate the time course of the detected slow and fast spindle sources, we considered the first four NREM sleep cycles and divided each cycle into five intervals of equal duration. We confirmed the preferential localization in the frontal (Brodmann area 10) and parietal (Brodmann area 7) cortical regions, respectively for slow (11.0–12.5) and fast (13.0–14.5) spindles. Across subsequent NREM sleep episodes, the maximal source activation remained systematically located in Brodmann area 10 and Brodmann area 7, showing the topographical stability of the detected generators. However, a different time course was observed as a function of the type of spindles: a linear decrease across subsequent cycles was found for slow spindle but not for fast spindle source. The intra-cycle variations followed a “U” shaped curve for both spindle source, with a trough around third and fourth interval (middle part) and the highest values at the beginning and the end of the considered temporal window.We confirmed the involvement of the frontal and parietal brain regions in spindle generation, showing for the first time their changes within and between consecutive NREM sleep episodes. Our results point to a correspondence between the scalp-recorded electrical activity and the underlying source topography, supporting the notion that spindles are not uniform phenomena: complex region- and time-specific patterns are involved in their generation and manifestatio