Carlo Cipolli

Recalling and Forgetting Dreams: Theta and Alpha Oscillations during Sleep Predict Subsequent Dream Recall

Under the assumption that dream recall is a peculiar form of declarative memory, we have hypothesized that (1) the encoding of dream contents during sleep should share some electrophysiological mechanisms with the encoding of episodic memories of the awake brain and (2) recalling a dream(s) after awakening from non-rapid eye movement (NREM) and rapid eye movement (REM) sleep should be associated with different brain oscillations. Here, we report that cortical brain oscillations of human sleep are predictive of successful dream recall. In particular, after morning awakening from REM sleep, a higher frontal 5–7 Hz (theta) activity was associated with successful dream recall. This finding mirrors the increase in frontal theta activity during successful encoding of episodic memories in wakefulness. Moreover, in keeping with the different EEG background, a different predictive relationship was found after awakening from stage 2 NREM sleep. Specifically, a lower 8–12 Hz (alpha) oscillatory activity of the right temporal area was associated with a successful dream recall. These findings provide the first evidence of univocal cortical electroencephalographic correlates of dream recall, suggesting that the neurophysiological mechanisms underlying the encoding and recall of episodic memories may remain the same across different states of consciousness.

Prioritized Detection of Personally Familiar Faces

We investigated whether personally familiar faces are preferentially processed in conditions of reduced attentional resources and in the absence of conscious awareness. In the first experiment, we used Rapid Serial Visual Presentation (RSVP) to test the susceptibility of familiar faces and faces of strangers to the attentional blink. In the second experiment, we used continuous flash interocular suppression to render stimuli invisible and measured face detection time for personally familiar faces as compared to faces of strangers. In both experiments we found an advantage for detection of personally familiar faces as compared to faces of strangers. Our data suggest that the identity of faces is processed with reduced attentional resources and even in the absence of awareness. Our results show that this facilitated processing of familiar faces cannot be attributed to detection of low-level visual features and that a learned unique configuration of facial features can influence preconscious perceptual processing.

Slow EEG rhythms and inter-hemispheric synchronization across sleep and wakefulness in the human hippocampus

Converging data that attribute a central role to sleep in memory consolidation have increased the interest to understand the characteristics of the hippocampal sleep and their relations with the processing of new information. Neural synchronization between different brain regions is thought to be implicated in long-term memory consolidation by facilitating neural communication and by promoting neural plasticity. However, the majority of studies have focused their interest on intra-hippocampal, rhinal-hippocampal or cortico-hippocampal synchronization, while inter-hemispheric synchronization has been so far neglected. To clarify the features of spontaneous human hippocampal activity and to investigate inter-hemispheric hippocampal synchronization across vigilance states, pre-sleep wakefulness and nighttime sleep were recorded from right and left homologous hippocampal loci using stereo-EEG techniques. Hence, quantitative and inter-hemispheric coherence analyses of hippocampal activity across sleep and waking states were carried out. The results showed the presence of delta activity in human hippocampal spontaneous EEG also during wakefulness. The activity in the delta range exhibited a peculiar bimodal distribution, namely a low frequency non-oscillatory activity (up to 2 Hz) synchronized between hemispheres mainly during wake and REM sleep, and a faster oscillatory rhythm (2-4 Hz). The latter was less synchronized between the hippocampi and seemed reminiscent of animal RSA (rhythmic slow activity). Notably, the low-delta activity showed high inter-hemispheric hippocampal coherence during REM sleep and, to a lesser extent, during wakefulness, paralleled by a (unexpected) decrease of coherence during NREM sleep. Therefore, low-delta hippocampal state-dependent synchronization starkly contrasts with neocortical behavior in the same frequency range. Further studies might shed light on the role of these low frequency rhythms in the encoding processes during wakefulness and in the consolidation processes during subsequent sleep.

Sleep, Dreams and memory: an overview

SUMMARY  Investigations into the role played by sleep in information processing have consistently shown that the retention of information is better when the memory storage is followed by a period of sleep than of waking. Less definitive evidence, however, is available as to whether the better performance is mainly due to (a) reduction of interference during sleep, (b) slowing down of decay, or (c) consolidation processes at work during sleep. Important insights as to whether consolidation takes place during sleep have recently been provided by the thematic continuity of dreams elaborated in the same night and by the repeated incorporation of pre‐sleep stimuli into dream contents. The analysis of such aspects of dreaming indicates that the items of information which are repeatedly accessed during sleep and elaborated for insertion into the ongoing dream experience are better retained at delayed recall. Finally, it is suggested that the use of the strategies applied in studying the information processing in normals may also be extended to sleep‐disturbed individuals, in order to establish how memory functioning during sleep is influenced by sleep disturbances.

Sleep-dependent memory consolidation in patients with sleep disorders

Sleep can improve the off-line memory consolidation of new items of declarative and non-declarative information in healthy subjects, whereas acute sleep loss, as well as sleep restriction and fragmentation, impair consolidation. This suggests that, by modifying the amount and/or architecture of sleep, chronic sleep disorders may also lead to a lower gain in off-line consolidation, which in turn may be responsible for the varying levels of impaired performance at memory tasks usually observed in sleep-disordered patients. The experimental studies conducted to date have shown specific impairments of sleep-dependent consolidation overall for verbal and visual declarative information in patients with primary insomnia, for verbal declarative information in patients with obstructive sleep apnoeas, and for visual procedural skills in patients with narcolepsy-cataplexy. These findings corroborate the hypothesis that impaired consolidation is a consequence of the chronically altered organization of sleep. Moreover, they raise several novel questions as to: a) the reversibility of consolidation impairment in the case of effective treatment, b) the possible negative influence of altered prior sleep also on the encoding of new information, and c) the relationships between altered sleep and memory impairment in patients with other (medical, psychiatric or neurological) diseases associated with quantitative and/or qualitative changes of sleep architecture.

How we remember the stuff that dreams are made of: Neurobiological approaches to the brain mechanisms of dream recall

Intrinsic and historical weaknesses delayed the spread of a sound neurobiological investigation on dreaming. Nevertheless, recent independent findings confirm the hypothesis that the neurophysiological mechanisms of encoding and recall of episodic memories are largely comparable across wakefulness and sleep. Brain lesion and neuroimaging studies converge in indicating that temporo-parieto-occipital junction and ventromesial prefrontal cortex play a crucial role in dream recall. Morphoanatomical measurements disclose some direct relations between volumetric and ultrastructural measures of the hippocampus-amygdala on the one hand, and some specific qualitative features of dreaming on the other. Intracranial recordings of epileptic patients also provide support for the notion that hippocampal nuclei mediate memory formation during sleep as well as in wakefulness. Finally, surface EEG studies showed that sleep cortical oscillations associated to a successful dream recall are the same involved in encoding and recall of episodic memories during wakefulness. Although preliminary, these converging pieces of evidence strengthen the general view that the neurophysiological mechanisms underlying episodic/declarative memory formation may be the same across different states of consciousness.

STORY-LIKE ORGANIZATION OF DREAM EXPERIENCE IN DIFFERENT PERIODS OF REM SLEEP

Four dream reports, collected from each of 16 subjects in an experimental night, were analysed using the criteria of Mandler and Johnsons story grammar. The experimental night was the first of the four nights where subjects had spontaneously given a dream report after each of the four awakenings planned in REM sleep. A multivariate analysis of covariance, taking the order of the nights where the experimental night occurred and the order of reports as factors, the number of stories per report as covariate and the number of statements in the setting, the number of statements in the event structure and number of episodes per story as dependent variables, showed that the greater length and complexity of reports collected in the second half of the night depends on a greater effectiveness of the dream production system rather than on a greater accuracy of recall. This increase concerns the organization of individual stories rather than the number of stories developed in a given time. These findings raise the issue of how dream production is re‐triggered during REM sleep. To cast light on this issue, it seems important to establish whether and how the themes of the various stories developed in a given dream experience are interrelated.

Active processing of declarative knowledge during REM-sleep dreaming

The ability to process recently acquired knowledge is clearly maintained during sleep. Here we assess whether and how far the sleeper controls this processing (in a non‐volitional and non‐conscious manner). We posit that during sleep, the cognitive concerns of previous waking may guide access to, and processing of, items of declarative knowledge with which those concerns are associated. In a delayed recall task, before each of three sleep onsets in the same night, 12 subjects heard a different nonsense sentence. When awakened in rapid eye movement (REM) sleep, they were asked to report their dream experience and to recall the last sentence heard. Occurrences of incorporation into dream content were more frequent for this sentence than for the sentences heard before previous sleep onsets, and also more frequent than occurrences of similar contents in reports from a control night. However, the modalities of elaboration of dream contents did not vary. These findings indicate that cognitive concern can affect the accessing of recently acquired declarative knowledge during sleep, but not the modalities by which this is inserted into dream content. They also suggest that cognitive concern may help consolidate knowledge by increasing the likelihood of it being processed during sleep.

The Validity of Informant Reports in Assessing the Severity of Dementia: Evidence from the CAMDEX Interview

The evaluation of a patient’s mental state, overall clinical profile and behavioural disturbance in the process of diagnosing dementia requires at least two sources of information: the patient and the informant. Since the severity of the dementia may interfere with the subjective perception of these disorders, it is important to evaluate the consistency between these two sources of information and the clinical and psychometric evaluation made by the physician. Accordingly, in this study five behavioural areas, derived from the semi-structured interview schedule provided by the Cambridge Examination for Mental Disorders of the Elderly (CAMDEX, i.e., Sleep, Depressed Mood, Everyday Activity, Memory and Global Mental Functioning) have been tested on the patient and his/her informant. Eighty dementia patients (mean age = 74 years) and their informants participated in the study. The dementia group was subdivided into two levels of severity according to DSM-IIIR criteria: 41 with mild dementia and 39 with moderate dementia, respectively, matched for age and schooling. The rating of impairment was found to increase along with the severity of dementia in all the above-mentioned areas, except for sleep. However, the source of information per se significantly influenced the evaluation of memory functioning. Moreover, the significant interaction between the two factors considered indicates that memory functioning is evaluated quite differently by the patients and the informants, as only in the assessment made by the latter group did the impairment increase in parallel with severity of dementia. Finally, whereas none of the subjective measures recorded in the patients were significantly correlated with their test scores, the correlations between the informant memory appraisals and patient test results proved to be significant. The present findings confirm the validity of informant reports in assessing cognitive and memory disorders in early-stage dementia, as well as in distinguishing patients with mild from those with moderate dementia.

Dream structure in Parkinson's patients.

Dream reports of patients with Parkinsons disease (PD) were analyzed to ascertain whether cognitive deficits associated with this nonfocal brain pathology influence dream structure or dream recall. Fifteen outpatients with idiopathic PD were sampled (diagnosed from 1 to 10 years and currently in stage II or III of Hoehn and Yarhs scale); all were without psychiatric symptoms or major medical illnesses and were currently being treated with L-dopa. After an adaptation night in the sleep laboratory, each patient spent a night in which he/she was awakened at least twice in rapid eye movement sleep and asked to report dream experience. Thirteen patients were able to report at least one dream. Overall frequency of dream recall (71.4%) was fully compatible with normative data for the elderly. Multiple regression analyses showed that both the length of the dream report as story and the organization of contents into coherent episodes (analyzed using Mandler and Johnsons story grammar) varied significantly in relation to level of cognitive functioning and, in part, of language comprehension, but not in relation to age, illness duration, and dose of L-dopa.