Cholesterol dysregulation in peripheral blood mononuclear cells of Alzheimer's disease

Cholesterol and the immune system are involved in Alzheimer's Disease (AD). To investigate the relations among them, we compared the cholesterol content in peripheral blood mononuclear cells (PBMC) of cognitively healthy controls and patients with mild cognitive impairment (MCI) and AD in two independent samples. Free cholesterol content of PBMC was lower in MCI and AD patients, and was modulated by APOE genotype. A decrease of CD8+ and an increase of CD16+ was also found in AD patients. These results suggest that cholesterol levels in PBMCs may represent an early signature of the disease and support the involvement of immune system in AD.

JNK1 and JNK3: divergent functions in hippocampal metabolic-cognitive function

Background and aim

The appearance of alterations in normal metabolic activity has been increasingly considered a risk factor for the development of sporadic and late-onset neurodegenerative diseases. In this report, we induced chronic metabolic stress by feeding of a high-fat diet (HFD) in order to study its consequences in cognition. We also studied the effects of a loss of function of isoforms 1 and 3 of the c-Jun N-terminal Kinases (JNK), stress and cell death response elements.

Methods

Animals were fed either with conventional chow or with HFD, from their weaning until their sacrifice at 9 months. Before sacrifice, body weight, intraperitoneal glucose and insulin tolerance test (IP-GTT and IP‑ITT) were performed to evaluate peripheral biometrics. Additionally, cognitive behavioral tests and analysis of spine density were performed to assess cognitive function. Molecular studies were carried out to confirm the effects of metabolic stressors in the hippocampus relative to cognitive loss.

Results

Our studies demonstrated that HFD in Jnk3^−/− lead to synergetic responses. Loss of function of JNK3 led to increased body weight, especially when exposed to an HFD and they had significantly decreased response to insulin. These mice also showed increased stress in the endoplasmic reticulum and diminished cognitive capacity. However, loss of function of JNK1 promoted normal or heightened energetic metabolism and preserved cognitive function even when chronically metabolically stressed.

Conclusions

Downregulation of JNK3 does not seem to be a suitable target for the modulation of energetic-cognitive dysregulations while loss of function of JNK1 seems to promote a good metabolic-cognitive profile, just like resistance to the negative effects of chronic feeding with HFD.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00471-y.

Lactoferrin as Immune-Enhancement Strategy for SARS-CoV-2 Infection in Alzheimer's Disease Patients

Coronavirus 2 (SARS-CoV2) (COVID-19) causes severe acute respiratory syndrome. Severe illness of COVID-19 largely occurs in older people and recent evidence indicates that demented patients have higher risk for COVID-19. Additionally, COVID-19 further enhances the vulnerability of older adults with cognitive damage. A balance between the immune and inflammatory response is necessary to control the infection. Thus, antimicrobial and anti-inflammatory drugs are hopeful therapeutic agents for the treatment of COVID-19. Accumulating evidence suggests that lactoferrin (Lf) is active against SARS-CoV-2, likely due to its potent antiviral and anti-inflammatory actions that ultimately improves immune system responses. Remarkably, salivary Lf levels are significantly reduced in different Alzheimer's disease (AD) stages, which may reflect AD-related immunological disturbances, leading to reduced defense mechanisms against viral pathogens and an increase of the COVID-19 susceptibility. Overall, there is an urgent necessity to protect AD patients against COVID-19, decreasing the risk of viral infections. In this context, we propose bovine Lf (bLf) as a promising preventive therapeutic tool to minimize COVID-19 risk in patients with dementia or AD.

Effects of Nutrition on Cognitive Function in Adults with or without Cognitive Impairment: A Systematic Review of Randomized Controlled Clinical Trials

New dietary approaches for the prevention of cognitive impairment are being investigated. However, evidence from dietary interventions is mainly from food and nutrient supplement interventions, with inconsistent results and high heterogeneity between trials. We conducted a comprehensive systematic search of randomized controlled trials (RCTs) published in MEDLINE-PubMed, from January 2018 to July 2021, investigating the impact of dietary counseling, as well as food-based and dietary supplement interventions on cognitive function in adults with or without cognitive impairment. Based on the search strategy, 197 eligible publications were used for data abstraction. Finally, 61 articles were included in the analysis. There was reasonable evidence that dietary patterns, as well as food and dietary supplements improved cognitive domains or measures of brain integrity. The Mediterranean diet showed promising results, whereas the role of the DASH diet was not clear. Healthy food consumption improved cognitive function, although the quality of these studies was relatively low. The role of dietary supplements was mixed, with strong evidence of the benefits of polyphenols and combinations of nutrients, but with low evidence for PUFAs, vitamin D, specific protein, amino acids, and other types of supplements. Further well-designed RCTs are needed to guide the development of dietary approaches for the prevention of cognitive impairment.

Impact of sleep loss before learning on cortical dynamics during memory retrieval

Evidence shows that sleep loss before learning decreases activation of the hippocampus during encoding and promotes forgetting. But it remains to be determined which neural systems are functionally affected during memory retrieval after one night of recovery sleep. To investigate this issue, we evaluated memory for pairs of famous people's faces with the same or different profession (i.e., semantically congruent or incongruent faces) after one night of undisturbed sleep in subjects who either underwent 4hours of acute sleep restriction (ASR, N=20) or who slept 8hours the pre-training night (controls, N=20). EEG recordings were collected during the recognition memory task in both groups, and the cortical sources generating this activity localized by applying a spatial beamforming filter in the frequency domain. Even though sleep restriction did not affect accuracy of memory performance, controls showed a much larger decrease of alpha power relative to a baseline period when compared to sleep-deprived subjects. These group differences affected a widespread frontotemporoparietal network involved in retrieval of episodic/semantic memories. Regression analyses further revealed that associative memory in the ASR group was negatively correlated with alpha power in the occipital regions, whereas the benefit of congruency in the same group was positively correlated with delta power in the left lateral prefrontal cortex. Retrieval-related decreases of alpha power have been associated with the reactivation of material-specific memory representations, whereas increases of delta power have been related to inhibition of interferences that may affect the performance of the task. We can therefore draw the conclusion that a few hours of sleep loss in the pre-training night, though insufficient to change the memory performance, is sufficient to alter the processes involved in retrieving and manipulating episodic and semantic information.

Individual and contextual factors associated to smoking on school premises

INTRODUCTION

Despite regulations, tobacco consumption in schools is still very common. The objective was to evaluate the relationship of personal, family, and school-level contextual factors with smoking on school premises.

METHODS

A representative survey was undertaken of students in the 4th year of secondary education in the Madrid region (Spain), including 79 schools and 3,622 individuals. The student questionnaire gathered information about personal and family variables. The contextual factors were type of school, perception of compliance with the law, smoking policy, existence of complaints against smoking, and undertaking of educational activities regarding smoking. Analysis was carried out in the smoking population (n = 1,179) using multilevel logistic regression models.

RESULTS

During the last 30 days, 50.6% of smokers had smoked on school premises. Having a father with a university education (in comparison with fathers who have not attained any educational level) reduces this probability (odds ratio [OR]: 0.43; 95% CI: 0.19-0.96), whereas smoking a larger number of cigarettes (p < .001), illicit drug consumption (p < .001), and low academic achievement (p = .052) increases it. The probability is reduced when there is no parental permission to smoke (OR: 0.66; 95% CI: 0.43-1.01) and is lower both in nonsubsidized private schools (OR: 0.29; 95% CI: 0.12-0.67) and in state subsidized private schools (OR: 0.17; 95% CI: 0.09-0.34) than in public schools.

CONCLUSIONS

A very low level of educational attainment by the father, smoking a higher number of cigarettes, as well as illicit drug consumption, low academic achievement, having parental permission to smoke, and attending public schools are all related to a higher probability of smoking on school premises.

Associative memory deficits in mild cognitive impairment: the role of hippocampal formation

Neuropathological events featuring early stages of Alzheimer's disease (AD) appear in the entorhinal cortex (EC), subiculum (SB) and cornu ammonis 1 (CA1) of hippocampus, which may account for associative memory deficits in non-demented people with mild cognitive impairment (MCI). To test this hypothesis in vivo, we investigated whether volume changes in these regions are related to failures in associative memory in MCI as compared to cognitively normal (CN) elderly subjects. Volume changes in EC and hippocampal subfields were determined by using deformation-based morphometry techniques applied to probabilistic cytoarchitectonic maps derived from post mortem human brains. CN subjects were distinguished from MCI patients by firstly identifying local volume differences in EC and hippocampus, and then evaluating the way in which these anatomical changes correlated with performance in a non-intentional face-location association task. MCI patients not only performed worse than CN elders in building new associations, but they were further unable to benefit from semantic encoding to improve episodic binding. According to our initial hypothesis, local volume reductions in both EC and hippocampal CA accounted for group differences in associative memory whereas atrophy in CA, but not in EC, accounted for semantic encoding of associations. Two main conclusions can be drawn from the present study: i) access to semantic information during encoding does not reduce the episodic deficit in MCI; and ii) EC and hippocampal CA, two regions early affected by AD neuropathology, are responsible, at least partially, for associative memory deficits observed in MCI patients.

Precise timing accounts for posttraining sleep-dependent enhancements of the auditory mismatch negativity

Memory consolidation is a long-lasting dynamic process by which new acquired information is transformed at different analysis levels, from molecules to cognition, without additional practice. Results from a previous study on event-related potentials (ERPs) suggest that part of the neural events promoting changes in the electrophysiological correlates of enhanced automatization in a sound discrimination task occur during sleep. These data were reanalyzed in the present study at the single-trial level, and results indicated that the first night of sleep succeeding training is absolutely required to improve the timing consistency of cortical neural assemblies involved in automatic sound-change detection, as revealed by a significant reduction in the latency-jitter of the MMN response across trials. This change in the regularity of the brain response to previously trained sounds facilitated involuntary switch of attention towards the same sounds when they were task irrelevant, as reflected by the P3a emergence after posttraining sleep. Both responses were, however, prevented in subjects deprived of sleep the night following training in the sound discrimination task. We hypothesize that the reduction in the MMN latency-jitter, which, in turn, triggered an automatic shift of attention, might result from a change in synaptic efficacy and/or neural excitability, rather than from changes in firing synchronization and/or size of representation.

Sensory and motor attentional modulation during the manual gap effect in humans: a high-density ERP study

The present study investigated reaction time (RT) and event-related potential (ERP) differences between gap and step conditions using visual stimulation and manual responses. RTs during the gap condition were facilitated with respect to those of the step condition. The ERPs, which were obtained from electrodes placed at 58 scalp sites, showed differences when the gap and step conditions were compared for the following components: an early positive component centred at the vertex, an enhanced P1 component, a frontal negativity, a negative lateralized motor potential, and an increased P3. All these results suggest that the facilitation induced by the gap is mediated by a modulation of the neural circuits involved in sensory, motor, and cognitive functions.

Auditory information processing during human sleep as revealed by event-related brain potentials

The main goal of this review is to elucidate up to what extent pre-attentive auditory information processing is affected during human sleep. Evidence from event-related brain potential (ERP) studies indicates that auditory information processing is selectively affected, even at early phases, across the different stages of sleep-wakefulness continuum. According to these studies, 3 main conclusions are drawn: (1) the sleeping brain is able to automatically detect stimulus occurrence and trigger an orienting response towards that stimulus if its degree of novelty is large; (2) auditory stimuli are represented in the auditory system and maintained for a period of time in sensory memory, making the automatic-change detection during sleep possible; and (3) there are specific brain mechanisms (sleep-specific ERP components associated with the presence of vertex waves and K-complexes) by which information processing can be improved during non-rapid eye movement sleep. However, the remarkably affected amplitude and latency of the waking-ERPs during the different stages of sleep suggests deficits in the building and maintenance of a neural representation of the stimulus as well as in the process by which neural events lead to an orienting response toward such a stimulus. The deactivation of areas in the dorsolateral pre-frontal cortex during sleep contributing to the generation of these ERP components is hypothesized to be one of the main causes for the attenuated amplitude of these ERPs during human sleep.

The initial orienting response during human REM sleep as revealed by the N1 component of auditory event-related potentials

The large N1 wave of the auditory event-related potentials (ERPs) typically occurring to the first stimulus after a long silent interval seems to be associated with the involuntary initial-orienting response. Since the mechanisms involved in the generation of this brain response are assumed to be activated automatically, the present study aims at determining whether this electrophysiological response can also be elicited during human REM sleep, the sleep stage considered most sensitive to external stimuli. To achieve this goal, the auditory N1 wave was analyzed in wakefulness and REM sleep for frequency deviant tones delivered in several positions (1, 2, 4 and 6) within homogenous stimulus trains separated by different intervals of silence (3, 6 and 9 s), the intra-train stimulus interval being 600 ms. A significant increment in the amplitude of the N1 component for the first deviant tone, as compared with deviants delivered in remaining positions, was observed in both brain states, independently of the inter-train interval length. This result cannot be explained by a release-from-refractoriness effect, since only one deviant was presented in each train and the inter-deviant interval hardly changed from one train to another. The increase in N1 to the first stimulus of the train, probably due to the contribution of the neuronal elements responsible for the supratemporal and non-specific components, may be explained by changes in the silent interval, rather than by variations in the stimulus frequency. The enhanced N1 could be reflecting a general increase in sensory sensitivity associated with the arousal factor of the orienting response. These findings suggest that the brain maintains the potential ability to trigger the brain events responsible for the OR elicitation, even during REM sleep.

Complex sound processing during human REM sleep by recovering information from long-term memory as revealed by the mismatch negativity (MMN)

Perceptual learning is thought to be the result of neural changes that take place over a period of several hours or days, allowing information to be transferred to long-term memory. Evidence suggests that contents of long-term memory may improve attentive and pre-attentive sensory processing. Therefore, it is plausible to hypothesize that learning-induced neural changes that develop during wakefulness could improve automatic information processing during human REM sleep. The MMN, an objective measure of the automatic change detection in auditory cortex, was used to evaluate long-term learning effects on pre-attentive processing during wakefulness and REM sleep. When subjects learned to discriminate two complex auditory patterns in wakefulness, an increase in the MMN was obtained in both wake and REM states. The automatic detection of the infrequent complex auditory pattern may therefore be improved in both brain states by reactivating information from long-term memory. These findings suggest that long-term learning-related neural changes are accessible during REM sleep as well.

State-modulation of cortico-cortical connections underlying normal EEG alpha variants

Normal electroencephalographic (EEG) alpha variants appear during relaxed wakefulness with closed eyes, drowsiness period at sleep onset, and rapid eye movement (REM) sleep in bursts without arousal signals. Previous results revealed that fronto-occipital and fronto-frontal alpha coherences became weaker from wakefulness to drowsiness, and finally to REM sleep. The present work was aimed at determining whether a generalized or a unidirectional deactivation of the long fronto-occipital fasciculi, previously proposed to be involved in the alpha rhythm generation, could explain the above-mentioned results. Polynomial regression analyses, applied to the change of alpha coherence with distance along the antero-posterior axis, suggested that the anterior and posterior local circuits show a similar level of activation in all brain states. Bivariate partial correlation analyses between local alpha coherences revealed that such local circuits maintain a reciprocal dependency during wakefulness, but unidirectional during drowsiness (anterior-to-posterior, A-P) and REM sleep (posterior-to-anterior, P-A). From these findings, both anterior and posterior cortical structures are suggested as being involved in the generation of the three alpha variants. If the implication of a double cortical generation source (anterior and posterior) of alpha variants is assumed, these two generators seem to maintain a mutual inter-dependency during wakefulness, whereas during the transition to human sleep, the anterior areas work quite independently of the posterior regions. Finally, the occipital structures may be the driving force for the REM-alpha bursts generation, since involvement of frontal regions demonstrated a high dependence on the posterior neural circuits in the genesis of this sleep event.

Spectral features of EEG alpha activity in human REM sleep: two variants with different functional roles?

Evidence suggests that an important contribution of spectral power in the alpha range is characteristic of human REM sleep. This contribution is, in part, due to the appearance of well-defined bursts of alpha activity not associated with arousals during both tonic and phasic REM fragments. The present study aims at determining if the REM-alpha bursts constitute a different alpha variant from the REM background alpha activity. Since previous findings showed a selective suppression of background alpha activity over occipital regions during phasic REM fragments and, on the other hand, the density of alpha bursts seem to be independent of the presence or absence of rapid eye movements, one expects to find the same spectral power contribution of alpha bursts in tonic and phasic REM fragments. The results indicated that REM-alpha bursts showed a similar power contribution and topographic distribution (maximum energy over occipital regions) both in tonic and phasic REM fragments. This suggests that two variants of alpha activity with different functional roles are present during the human REM sleep: i) background alpha activity, modulated over occipital regions by the presence of rapid eye movements, which may be an electrophysiological correlate of the visual dream contents; and ii) REM-alpha bursts, independent of the presence of rapid eye movements, which could be facilitating the connection between the dreaming brain and the external world, working as a micro-arousal in this brain state.

[Clinical value of EEG coherence as electrophysiological index of cortico-cortical connections during sleep]

OBJECTIVE

The technique of EEG coherence gives a non-invasive objective index of the functional relations between the different regions of the cerebral cortex. The main objectives of this study were firstly to obtain methodological information to facilitate its use in any context, whether clinical or in investigation, and secondly to draw attention to the results obtained with this technique during the different phases of sleep, both in healthy persons and in certain clinical conditions where its use in evaluation and/or diagnosis has been shown.

DEVELOPMENT

The results derived from the application of coherence analysis during normal sleep show the existence of a high level of interhemisphere connectivity during all phases of sleep. This result has fomented its use in the evaluation and diagnosis of disorders in which it is suspected that there are anomalies in the relation between the two hemispheres, such as neurological changes (agenesis of the corpus callosum, AIDS), psychiatric disorders (depression) and in the prognosis of states of coma. Also, progressive neurone degeneration and neurochemical deficits characteristic of Alzheimer-type dementia suggest that the coherence EEG during the REM phase may give electrophysiological indices in the establishment of the diagnosis and prognosis of the disorder.

CONCLUSION

This study shows that the coherence technique is a useful tool when establishing the pattern of cortico-cortical interactions subjacent to different functional states of the brain, both in healthy persons and in those with the different diseases in which there are alterations in cerebral function.

Spectral structure and brain mapping of human alpha activities in different arousal states

In a study with 10 young, healthy subjects, alpha activities were studied in three different arousal states: eyes closed in relaxed wakefulness (EC), drowsiness (DR), and REM sleep. The alpha band was divided into three subdivisions (slow, middle, and fast) which were analyzed separately for each state. The results showed a different spectral composition of alpha band according to the physiological state of the subject. Slow alpha seemed to be independent of the arousal state, whereas middle alpha showed a difference between REM and the other states. The fast-alpha subdivision appears mainly as a waking EEG component because of the increased power displayed only in wakefulness and lower and highly stable values for DR and REM. Scalp distribution of alpha activity was slightly different in each state: from occipital to central regions in EC, this topography was extended to fronto-polar areas in DR, with a contribution from occipital to frontal regions in REM sleep. These results provide evidence for an alpha power modulation and a different scalp distribution according to the cerebral arousal state.

Decay time of the auditory sensory memory trace during wakefulness and REM sleep

In a repetitive auditory stimulus sequence, deviant infrequent tones typically elicit a component of auditory event-related potentials termed mismatch negativity (MMN). The elicitation of MMN is assumed to reflect the existence of a memory trace of the standard stimulus that has a decay time of about 10 s and is strengthened by repetition of the standards. The main aim of the present study was to test the decay time of the sensory memory trace during rapid-eye movement (REM) sleep vs. wakefulness, as indexed by the MMN. Subjects were presented 10 tone trains, separated by 3, 6, or 9 s of silence, during waking and REM sleep. Each train consisted of 9 standards of 1000 Hz and 1 deviant of 2000 Hz that occurred at position 1, 2, 4, or 6. The waking deviants elicited a frontocentral negativity with a scalp topography equivalent to the MMN component. During REM sleep, the negative component showed the same scalp distribution only for the 3-s intertrain interval (ITI). In this brain state, the MMN amplitude was smaller and decreased with prolongation of the ITI. These results suggest a weaker sensory memory trace formation and a premature decay time of such a memory trace during REM sleep as compared with wakefulness.

Spectral and Topographic Microstructure of Brain Alpha Activity During Drowsiness at Sleep Onset and REM Sleep

Abstract High-resolution frequency methods were used to describe the spectral and topographic microstructure of human spontaneous alpha activity in the drowsiness (DR) period at sleep onset and during REM sleep. Electroencephalographic (EEG), electrooculographic (EOG), and electromyographic (EMG) measurements were obtained during sleep in 10 healthy volunteer subjects. Spectral microstructure of alpha activity during DR showed a significant maximum power with respect to REM-alpha bursts for the components in the 9.7-10.9 Hz range, whereas REM-alpha bursts reached their maximum statistical differentiation from the sleep onset alpha activity at the components between 7.8 and 8.6 Hz. Furthermore, the maximum energy over occipital regions appeared in a different spectral component in each brain activation state, namely, 10.1 Hz in drowsiness and 8.6 Hz in REM sleep. These results provide quantitative information for differentiating the drowsiness alpha activity and REM-alpha by studying their microstructural properties. On the other hand, these data suggest that the spectral microstructure of alpha activity during sleep onset and REM sleep could be a useful index to implement in automatic classification algorithms in order to improve the differentiation between the two brain states.

Prognostic influence of p53 nuclear overexpression in colorectal carcinoma

PURPOSE

The aim of this study was to test the prognostic influence of p53 nuclear overexpression in colorectal carcinoma.

METHODS

We performed an analysis of the prognostic influence of the nuclear overexpression of p53 with immunohistochemistry in 126 cases of colorectal carcinoma operated on in our hospital between 1987 and 1992, with a minimum follow-up time of 60 months (5 years).

RESULTS

Our results show a statistically significant prognostic influence of p53 overexpression on disease-free survival time, but not on the overall survival time, in univariate analysis, but this influence is lost in multivariate analysis.

CONCLUSIONS

Our results confirm recent reports by other authors that failed to show the independent prognostic value of p53 in colorectal carcinoma.

Alpha burst activity during human REM sleep: descriptive study and functional hypotheses

OBJECTIVES

Spectral power contribution in the range of alpha activity is a well-known electrophysiological feature of human REM sleep, which could be caused by the spontaneous bursts of alpha activity not associated with arousals that usually appear during this brain state. The present study was undertaken to determine the density of alpha bursts during tonic and phasic (oculomotor) REM periods for each REM cycle. In addition, this phasic brain event was also described from a spectral and topographical point of view.

METHODS

Ten healthy right-handed subjects (5 females) aged 19-25 years (mean 22.9 years, SD 2.6) participated in the present study. Each selected subject filled in a daily sleep log for 2 weeks before the experimental night to provide information on all 3 salient aspects of sleep pattern, sleep experience and sleep effects.

RESULTS

The results revealed that transient REM-alpha bursts, which lasted about 3 s and were accompanied by no increase in the EMG amplitude, appeared in all subjects who participated in this study, showing a higher density in the third and fourth REM cycle during phasic in comparison with tonic periods. The bandpass filtered signals showed the highest spectral contribution for the slower alpha components (8-9 Hz), the occipital scalp regions being the main generator source of this brain activity.

CONCLUSIONS

The authors hypothesize that REM-alpha bursts may work as micro-arousals (or incomplete arousals) facilitating the brain connection with the external world in this cerebral state, whereas REM-alpha arousals - usually longer and accompanied by changes in the EMG amplitude - generate a shift of brain state associated with sleep fragmentation (complete arousal).

Alpha EEG coherence in different brain states: an electrophysiological index of the arousal level in human subjects

The functional relationships between the brain areas supposedly involved in the generation of the alpha activity were quantified by means of INTRA- and INTER-hemispheric coherences during different arousal states (relaxed wakefulness, drowsiness at sleep onset, and rapid eye movement sleep) where such an activity can be clearly detectable in the human EEG. A significant decrease in the fronto-occipital as well as in the inter-frontal coherence values in the alpha range was observed with the falling of the vigilance level, which suggests that the brain mechanisms underlying these coherences are state dependent. Making fronto-frontal coherence values in the alpha frequency band useful indexes to discern between brain functional states characterized by a different arousal level.

Brain spatial microstates of human spontaneous alpha activity in relaxed wakefulness, drowsiness period, and REM sleep

Spontaneous alpha activity clearly present in relaxed wakefulness with closed eyes, drowsiness period at sleep onset, and REM sleep was studied with spatial segmentation methods in order to determine if the brain activation state would be modulating the alpha spatial microstates composition and duration. These methods of spatial segmentation show some advantages: i) they extract topographic descriptors independent of the chosen reference (reference-free methods), and ii) they achieve spatial data reduction that are more data-driven than dipole source analysis. The results obtained with this study revealed that alpha activity presented a different spatio-temporal pattern of brain electric fields in each arousal state used in this study. These differences were reflected in a) the mean duration of alpha microstates (longer in relaxed wakefulness than in drowsy period and REM sleep), b) the number of brain microstates contained in one second (drowsiness showed more different microstates than did relaxed wakefulness and REM state), and c) the number of different classes (more abundant in drowsiness than in the rest of brain states). If we assume that longer segments of stable brain activity imply a lesser amount of different information to process (as reflected by a higher stability of the brain generator), whereas shorter segments imply a higher number of brain microstates caused by more different steps of information processing, it is possible that the alpha activity appearing in the sleep onset period could be indexing the hypnagogic imagery self-generated by the sleeping brain, and a phasic event in the case of REM sleep. Probably, REM-alpha bursts are associated with a brain microstate change (such as sleep spindles), as demonstrated by its phasic intrusion in a desynchronized background of brain activity. On the other hand, alpha rhythm could be the "baseline" of brain activity when the sensory inputs are minimum and the state is relaxed wakefulness.

Alpha power modulation during periods with rapid oculomotor activity in human REM sleep

Alpha activity attenuation (blocking) over occipital regions is an electrophysiological index of cortical activation associated with visual attention and waking mental imagery. The present work focused on exploring whether the human REM background alpha activity was modulated, attending to tonic- (without rapid oculomotor activity) and phasic-REM periods (with a prominent burst of REMs). The obtained results revealed that the background alpha activity showed a decreased spectral power over occipital brain regions during phasic-REM in comparison with tonic-REM periods. This result suggests an active visual processing caused by the complex mental imagery generated during periods of oculomotor activity in human REM sleep.

[Cerebral mapping during sleep: a critical review of literature]

INTRODUCTION

Cerebral mapping is a useful tool which permits graphic representation of certain EEG characteristics which are imperceptible on simple visual inspection. This technique offers quite a good solution to analysis of cerebral rhythmicity, by including spectral, spatial and statistical parameters. Sleep is a physiological process during which dynamic interchange of cerebral rhythms has an important part in delimiting the different phases, not to mention the decisive part played by phasic events at each stage of it.

DEVELOPMENT

In this paper we review the studies which have used cerebral mapping techniques during the different stages of sleep. In order to give structure to the data obtained from these papers, we have classified the information into aspects related to the methodology used in these studies and the results obtained. Decisions regarding methodology are discussed, and further information given regarding technical aspects which might have had decisive influence on the results obtained using this technique.

CONCLUSIONS

We give suggestions as to the possibilities of the use of cerebral mapping in studies on sleep, both clinically and experimentally.

The mismatch negativity component reveals the sensory memory during REM sleep in humans

Auditory evoked potentials (AEPs) were recorded during presentation of stimuli of 1000 Hz (standard) and 2000 Hz (deviant) in trains of 10 tone bursts (one deviant per train) in the wake and rapid eye movement (REM) sleep states. The constant inter-stimulus interval (ISI) was 600 ms and the trains were separated by 3 s of silence. The deviant tone occurring at the train start elicited a mismatch negativity component (MMN) in both arousal states, displaying a peak latency between 100 and 150 ms post-stimulation at fronto-central areas. These results suggest the existence of an auditory memory trace (sensory memory) surviving for at least 3 s during REM sleep.

National survey on laparoscopic cholecystectomy in Spain. Results of a multiinstitutional study conducted by the Committee for Endoscopic Surgery (Associación Española de Cirujanos)

We present a joint study conducted by the Committee for Endoscopic Surgery in Spain. Sixty-nine surgeons reported 2,342 laparoscopic cholecystectomies (LCs) performed until November 1992. The conversion rate was 5.1%. The overall morbidity was 7.1%. The biliary morbidity was 0.45%: Seven severe bile duct injuries were recognized at laparoscopy (0.28%) and four lesions were postoperatively diagnosed (0.16%). Bile leak unrelated to bile duct lesion occurred in 14 patients (0.7%), leading to five reoperations. The mortality was 0.12% and was unrelated to the laparoscopic approach in two cases. The risk factors for biliary complications were obesity, previous history of jaundice, and previous hospital admissions. Surgeon experience was defined by 50 LCs performed and the overall complication rate presented a statistically significant relation to surgeon experience (P < 0.001).