False memories in obstructive sleep apnoea syndrome: evidence from the divided attention paradigm at encoding or retrieval.

Patients with obstructive sleep apnoea syndrome (OSAS) exhibit impaired retrieval of item-specific information, increasing their propensity to generate false recognitions. The present study investigated the effect of OSAS on false recognition, using a divided-attention paradigm to examine whether reducing the availability of attentional resources during encoding or retrieval in healthy participants mimics the effect of OSAS. We tested four groups of participants, using the Deese - Roediger - McDermott paradigm: patients with OSAS and controls, either under full attention or under divided attention at encoding or retrieval. Results showed that divided attention at retrieval, but not at encoding, mimicked the effects of OSAS on memory performance, as controls in this group exhibited a higher level of false recognition than those under full attention, but a similar level of correct recognition. Our results suggest that the greater susceptibility of patients with OSAS to false recognition may be due to a limited availability of attentional resources, which may specifically disrupt retrieval processes.

Human Voice as a Measure of Mental Load Level.

PURPOSE: The aim of this study was to determine a reliable and efficient set of acoustic parameters of the human voice able to estimate individuals' mental load level. Implementing detection methods and real-time analysis of mental load is a major challenge for monitoring and enhancing human task performance, especially during high-risk activities (e.g., flying aircraft). METHOD: The voices of 32 participants were recorded during a cognitive task featuring word list recall. The difficulty of the task was manipulated by varying the number of words in each list (i.e., between 1 and 7, corresponding to 7 mental load conditions). Evoked pupillary response, known to be a useful proxy of mental load, was recorded simultaneously with speech to attest variations in mental load level during the experimental task. RESULTS: Classic features (fundamental frequency, its standard deviation, number of periods) and original features (frequency modulation and short-term variation in digital amplitude length) of the acoustic signals were predictive of memory load condition. They varied significantly according to the number of words to recall, specifically beyond a threshold of 3-5 words to recall, that is, when memory performance started to decline. CONCLUSIONS: Some acoustic parameters of the human voice could be an appropriate and efficient means for detecting mental load levels.

Increased phantom recollection after sleep.

Sleep is known to benefit memory consolidation, but its effect on false memory is less clear. We applied the simplified conjoint recognition paradigm to investigate how sleep affects the cognitive processes behind correct or false recognition, according to fuzzy-trace theory, and measured the retrieval of verbatim traces, retrieval of gist traces, and phantom recollection. Participants studied 24 lists of semantically related words lacking the strongest common associate or theme word. Recognition was tested 12 h later, following either a night's sleep or daytime wakefulness. The recognition test featured studied words, nonstudied theme words (false recognition), and unrelated words. False recognition rate was higher after sleep than after daytime wakefulness. True recognition rate was the same. Analysis of the cognitive processes underlying recognition showed that phantom recollection was higher after sleep. Assuming that phantom recollection reflects the retrieval of strong gist traces, sleep may strengthen gist traces and promote gist extraction.

Cannabis smoking impairs driving performance on the simulator and real driving: a randomized, double-blind, placebo-controlled, crossover trial.

Driving experiments in real conditions are considered as a 'gold standard' to evaluate the effects of drugs on driving performance. Several constraints are difficult to manage in these conditions, so driving simulation appears as the best alternative. A preliminary comparison is crucial before being able to use driving simulation as a valid evaluation method. The aim of this study was to design a driving simulation method for assessing drug effects on driving. We used cannabis (THC) as a positive control and assessed whether THC affects driving performance in simulation conditions and whether these effects are consistent with performance in real driving conditions. A double-blind, placebo-controlled, two successive two-way crossover design was performed using cigarettes containing 20 mg of THC. Healthy occasional users of THC, aged 25-35 years, who had a consistent driving experience were included. The first two sessions were realized in simulation conditions, and the last two sessions were in real driving conditions. Driving performance was estimated through inappropriate line crossings (ILC) and the standard deviation of the vehicle's lateral position. Participants felt significantly drowsier and more tired after THC, whatever the driving condition. Driving stability was significantly impaired after THC, both in simulated and real driving conditions. We also found that ILC were significantly more numerous in driving simulation conditions, as compared to real driving. In conclusion, the driving simulator was proven to be more sensitive for demonstrating THC-induced effects on driving performances. Driving simulation appears to be a good qualitative predictor of driving safety after drug intake.

Obstructive sleep apnoea syndrome increases source-confusion errors: A pilot study.

We explored external source monitoring (i.e., discrimination between memories of two externally derived sources) in patients with obstructive sleep apnoea syndrome (OSAS). Our specific aim was to ascertain whether, relative to controls, patients exhibit more source-confusion errors when there are similarities between two external memory sources. We recruited 22 patients with OSAS and 22 controls matched for sex, age, and education. The experimental procedure we used came in three phases. First, participants viewed a target film. Second, they were shown a mixed set of photographs, some taken from the film (target photographs), others not (photographs taken from other films not viewed by participants; lures). Lures differed either conceptually or perceptually from the target film. Third, the following day, participants were shown a set of photographs and urged to determine whether the photographs were taken from the target film or whether they were images they had seen for the first time in Phase 2. Patients correctly attributed the same number of target photographs to the target film as controls. By contrast, they incorrectly attributed more lures to the target film than controls did, especially when the lures were semantically similar to the film (perceptual lures). Both perceptual and conceptual source-confusion errors were significantly correlated with oxygen desaturation during sleep. Results suggest that the higher number of source-confusion errors observed in patients with OSAS was linked to an impaired ability to recollect specific perceptual details of the study items and that hypoxia is the main contributing factor to this deficit.

[Obstructive sleep apnea syndrome and cognition: A review]. / Syndrome d'apnées obstructives du sommeil et cognition : une revue.

Obstructive sleep apnea syndrome (OSAS) is a sleep-related breathing disorder characterized by repetitive episodes of airflow cessation, resulting in brief arousals and intermittent hypoxemia. OSAS is associated with a number of adverse health consequences, and cognitive difficulties. The overall pattern of cognitive impairment in OSAS is complex, and research in this field is mixed. On balance, OSAS have negative effects on cognition, most likely in the domain of attention/vigilance, verbal and visual delayed long-term memory, and executive functions. A still unanswered question is whether these deficits are primarily a consequence of sleep fragmentation and/or hypoxemia, or whether they coexist independently from OSAS. Continuous positive airway pressure (CPAP) is the most effective and widely used treatment of OSAS. No consistent effect of CPAP use on cognitive performance was evident. This may be due, in part, to variability in study design and sampling methodology across studies. Structural changes have been reported in different brain regions, particularly in hippocampus and frontal cortex. Recent evidence suggests that the OSAS-related structural changes may improve with CPAP treatment. However, one of the challenges is to interpret the findings in light of comorbid conditions that also cause neural lesions. Animal models will be specifically useful to disentangle the different potential contributors to cognitive impairment in OSAS. The purpose of this article is to provide a review of the literature on cognition and neuroimaging in OSAS patients before and after CPAP treatment. We also discuss the mechanisms that have been proposed to explain cognitive deficits in OSAS patients.

Naturalistic conversation improves daytime motorway driving performance under a benzodiazepine: a randomised, crossover, double-blind, placebo-controlled study.

The adverse effects of benzodiazepines on driving are widely recognised. The aims of this study were both to determine the impact of naturalistic conversation on the driving ability of drivers under a benzodiazepine, and to measure the accuracy of drivers' assessments of the joint effects of the benzodiazepine and conversation. Sixteen healthy male participants (29.69 ± 3.30 years) underwent a randomised, crossover, double-blind, placebo-controlled study with the benzodiazepine lorazepam (2mg). They drove 200 km (125 miles) on a motorway in the morning. We measured two driving ability-related variables (i.e., lane-keeping performance), and collected a set of self-assessed variables (i.e., self-assessment of driving performance) during two 10-min sequences of interest (no conversation vs. conversation). An analysis of variance revealed an interaction whereby lane-keeping performance under lorazepam was worse in the no-conversation condition than in the conversation condition. No such difference was detected under placebo. Pearson's correlation coefficients revealed that self-assessments were (i) not at all predictive of lane-keeping when performed before the drive, but (ii) moderately predictive of lane-keeping performance when performed during or after the drive. We conclude that conversation with a passenger may contribute to safer lane-keeping when driving under a benzodiazepine. Moreover, a degree of awareness may be attained after some experience of driving under the influence of this type of medication.

Memory monitoring and memory control in patients suffering from obstructive sleep apnoea syndrome.

Patients with obstructive sleep apnoea syndrome exhibit memory deficit. The present study looked at whether this deficit is related to impaired memory monitoring and/or memory control. Here 25 patients and 26 healthy controls performed a paired-associate learning task. After participants had made a judgement of learning for each pair and performed an initial recall test they were free to restudy any items they wished, for as long or little as they wished, within a 5-minute period. They then performed a second recall test. Monitoring and control processes were assessed on the basis of judgements of learning, item selection, and study-time allocation. In spite of their memory impairment, patients accurately predicted their recall. For the restudy phase patients preferentially selected the judged-easy items, while controls selected the judged-difficult items. However, all the participants allocated more restudy time to the judged-difficult items than to the judged-easy ones. There were no significant correlations between memory performance, metamemory processes, and clinical measures (i.e., subjective sleepiness, subjective sleep quality, anxiety, and depression scores). Results suggested that both memory monitoring and memory control were preserved in our sample of patients with obstructive sleep apnoea.

Lorazepam impairs highway driving performance more than heavy alcohol consumption.

While research indicates that benzodiazepine (BZD)-like drugs impair driving performance, it remains unclear (i) how far BZDs affect lane-keeping performance, compared with alcohol and (ii) to what extent this impact can realistically be measured in a simulated environment. To clarify these issues, 16 healthy male drivers who had never previously taken BZDs underwent a randomized, crossover, double-blind, placebo-controlled driving paradigm (with the BZD lorazepam) in both real-world and simulated settings. Two lane-keeping variables, namely inappropriate line crossings (ILCs) and standard deviation of lateral position (SDLP), were recorded during the driving sessions. Analyses revealed that (i) a single lorazepam dose (2 mg given by mouth) caused higher SDLP increases than a blood alcohol concentration of above 0.05%, and that (ii) this BZD effect was amplified in the simulated driving setting, mainly for ILCs. As a consequence, we recommend that physicians be made more aware of BZD-related risks and that researchers make a clear distinction between the effects of BZD intake per se and the impact of simulated driving settings.

Decision making is affected in obstructive sleep apnoea syndrome.

We assessed decision making in 20 patients newly diagnosed with obstructive sleep apnoea (OSA) and 20 healthy controls with the Iowa Gambling Task (IGT), which evaluates the ability to learn to sacrifice immediate rewards in favour of long-term gains. A standard neuropsychological battery was administered. Switching scores tended to be lower in patients. Patients persisted in selecting risky decks throughout the IGT, whereas controls behaved normally. Performance was correlated with hypoxaemia. Brain regions underlying decision making may be affected by OSA-related hypoxaemia.

Metamemory beliefs and episodic memory in obstructive sleep apnea syndrome.

This study assessed metamemory and its role in actual episodic memory performance in 26 patients with obstructive sleep apnea syndrome and 27 healthy controls. Metamemory knowledge and memory beliefs were assessed using the Metamemory Inventory in Adulthood. Episodic memory performance was investigated with the Remember/Know paradigm. Subjective sleepiness was evaluated. Patients underwent a polysomnographic assessment. In contrast to the control group's more stable memory beliefs, patients self-assessed their memory as declining across time, and felt more anxious about their memory. There was only a modest difference between patients' self-perceptions of their memory capacities and those of the control group, but patients' actual memory performance was strongly disturbed. While the latter was significantly correlated with severity of obstructive sleep apnea, scores on the Metamemory Inventory in Adulthood scales were not correlated with physiological measures, subjective sleepiness, or episodic memory performance. Obstructive sleep apnea may affect prefrontal cortex functioning and hence the ability to assess one's own memory impairment.

Spatial and temporal memories are affected by sleep fragmentation in obstructive sleep apnea syndrome.

This study evaluated episodic memory, with an emphasis on the recollection of spatial and temporal contexts, in 28 patients suffering from obstructive sleep apnea syndrome and 29 healthy controls. Recollection was assessed by means of the R/K paradigm and the process-dissociation procedure. Attentional abilities were also evaluated. A polysomnographic assessment, including nocturnal oxygen saturation and daytime sleepiness, was conducted. Recollection was strongly disturbed in patients, the number of microarousals being the best predictor of the memory deficit. Attention was only slightly disturbed. Results suggest a link between episodic memory deficit and those areas of the brain that are particularly sensitive to sleep fragmentation, in particular the hippocampus.

Slow wave sleep and recollection in recognition memory.

Recognition memory performance reflects two distinct memory processes: a conscious process of recollection, which allows remembering specific details of a previous event, and familiarity, which emerges in the absence of any conscious information about the context in which the event occurred. Slow wave sleep (SWS) and rapid eye movement (REM) sleep are differentially involved in the consolidation of different types of memory. The study assessed the effects of SWS and REM sleep on recollection, by means of the "remember"/"know" paradigm. Subjects studied three blocks of 12 words before a 3-h retention interval filled with SWS, REM sleep or wakefulness, placed between 3 a.m. and 6 a.m. Afterwards, recognition and recollection were tested. Recollection was higher after a retention interval rich in SWS than after a retention interval rich in REM sleep or filled with wakefulness. The results suggest that SWS facilitates the process of recollection in recognition memory.

Sleep strategies of 12-hour shift nurses with emphasis on night sleep episodes.

OBJECTIVES: Episodes of sleep during a nightshift are frequently reported in various types of jobs. This phenomenon has been seldom documented so far. This field study investigated individual differences in the sleep-wake behavior of nurses. METHODS: A group of eight nurses working in an intensive care unit on a two 12-hour shift system kept a "sleep diary" for 1 month, recording main sleep periods and naps. They subjectively assessed sleepiness, sleep quality, and the need for sleep at various times of the day and night. Continuous actimetric measurements provided an evaluation of the rest-activity patterns and of the sleep parameters. RESULTS: Half of the nurses chose to take naps in 75% of their nightshifts. No differences between the night-nappers and nonnight-nappers were found for either total sleep length or the temporal patterns of subjective sleepiness at night but, during nightwork, night-nappers needed sleep earlier than nonnight-nappers. They had long naps during a worknight and short daytime sleep, sometimes followed by a late afternoon nap. This strategy probably favored the maintenance of a diurnal orientation. Nonnight-nappers had long daytime sleep and took preventive naps to anticipate sleepiness during nightwork. However, their readjustment to diurnal life seemed more difficult than that of night-nappers. CONCLUSIONS: Nurses use different sleep-wake strategies to cope with nightwork. These different strategies may be due to circadian influence although social factors cannot be totally excluded.