Transient changes in frontal alpha asymmetry as a measure of emotional and physical distress during sleep

Influencing dreams through sensory stimulation: A systematic review

Sleep is typically considered a state of disconnection from the environment, yet instances of external sensory stimuli influencing dreams have been reported for centuries. Explaining this phenomenon could provide valuable insight into dreams' generative and functional mechanisms, the factors that promote sleep continuity, and the processes that underlie conscious awareness. Moreover, harnessing sensory stimuli for dream engineering could benefit individuals suffering from dream-related alterations. This PRISMA-compliant systematic review assessed the current evidence concerning the influence of sensory stimulation on sleep mentation. We included 51 publications, of which 21 focused on auditory stimulation, ten on somatosensory stimulation, eight on olfactory stimulation, four on visual stimulation, two on vestibular stimulation, and one on multimodal stimulation. Furthermore, nine references explored conditioned associative stimulation: six focused on targeted memory reactivation protocols and three on targeted lucid reactivation protocols. The reported frequency of stimulus-dependent dream changes across studies ranged from 0 to ∼80%, likely reflecting a considerable heterogeneity of definitions and methodological approaches. Our findings highlight a lack of comprehensive understanding of the mechanisms, functions, and neurophysiological correlates of stimulus-dependent dream changes. We suggest that a paradigm shift is required for meaningful progress in this field.

Sleep and dreaming in the light of reactive and predictive homeostasis

Dreams are often viewed as fascinating but irrelevant mental epihenomena of the sleeping mind with questionable functional relevance. Despite long hours of oneiric activity, and high individual differences in dream recall, dreams are lost into oblivion. Here, we conceptualize dreaming and dream amnesia as inherent aspects of the reactive and predictive homeostatic functions of sleep. Mental activity during sleep conforms to the interplay of restorative processes and future anticipation, and particularly during the second half of the night, it unfolds as a special form of non-constrained, self-referent, and future-oriented cognitive process. Awakening facilitates constrained, goal-directed prospection that competes for shared neural resources with dream production and dream recall, and contributes to dream amnesia. We present the neurophysiological aspects of reactive and predictive homeostasis during sleep, highlighting the putative role of cortisol in predictive homeostasis and forgetting dreams. The theoretical and methodological aspects of our proposal are discussed in relation to the study of dreaming, dream recall, and sleep-related cognitive processes.

Association between preoperative frontal electroencephalogram alpha asymmetry and postoperative quality of recovery: an observational study

BACKGROUND

Left-sided frontal alpha asymmetry on electroencephalograms, which indicates decreased relative left-hemispheric activity, has been associated with depression, anxiety, and stress responsivity. We aimed to evaluate the association between perioperative measures of frontal alpha asymmetry and quality of recovery (QoR) after surgery.

METHODS

We enrolled 110 female patients undergoing thyroidectomy and recorded perioperative electroencephalograms. The power of the prefrontal alpha band (8-13 Hz) was measured in the Fp1 and Fp2 leads. Left-sided frontal alpha asymmetry was defined as a higher alpha band power in Fp1 than in Fp2 and vice versa. QoR was assessed using the QoR-15 score on the day before surgery and postoperative days 1 and 2. The primary study endpoint was a difference in postoperative global QoR-15 score between preoperative left-sided and right-sided alpha asymmetry groups. The predictability of frontal alpha asymmetry for poor QoR-15 score was also evaluated.

RESULTS

The global QoR-15 score showed a significant group-by-time interaction, and post-hoc analysis revealed significantly lower scores on postoperative days 1 (P=0.006) and 2 (P<0.001) in the left-sided frontal alpha asymmetry group. In the multivariate logistic regression analysis, preoperative left-sided frontal alpha asymmetry was associated with a 3.3-fold increased risk of the lowest tertile for the postoperative day 1 QoR-15 score (95% CI: 1.31-8.24; P=0.011).

CONCLUSIONS

Preoperative left-sided frontal alpha asymmetry was independently associated with a lower postoperative QoR-15 score in female patients undergoing thyroidectomy, highlighting the potential role of preoperative frontal electroencephalography in predicting patient-centred outcomes after surgery.

CLINICAL TRIAL REGISTRATION

KCT0006586 (http://cris.nih.go.kr/).

Sleep spindle dynamics suggest over-consolidation in post-traumatic stress disorder

Devastating and persisting traumatic memories are a central symptom of post-traumatic stress disorder (PTSD). Sleep problems are highly co-occurrent with PTSD and intertwined with its etiology. Notably, sleep hosts memory consolidation processes, supported by sleep spindles (11–16 Hz). Here we assess the hypothesis that intrusive memory symptoms in PTSD may arise from excessive memory consolidation, reflected in exaggerated spindling. We use a newly developed spindle detection method, entailing minimal assumptions regarding spindle phenotype, to assess spindle activity in PTSD patients and traumatized controls. Our results show increased spindle activity in PTSD, which positively correlates with daytime intrusive memory symptoms. Together, these findings provide a putative mechanism through which the profound sleep disturbance in PTSD may contribute to memory problems. Due to its uniform and unbiased approach, the new, minimal assumption spindle analysis seems a promising tool to detect aberrant spindling in psychiatric disorders.

Feeling better or not: Adjusting affective style moderates the association between sleep duration and positive affect on next day

Affect is intertwined with sleep, yet how to adjust sleep duration to enhance affect remains unknown. Previous studies found that adjusting affective style, reflecting interindividual differences in emotion regulation, functions in processes where sleep modulates our affective state. Hence, this study examined whether and how it moderates the association between daily sleep duration and subsequent affect. An ambulatory assessment design was employed among 64 participants, wherein both within-person sleep duration and affect, and between-person affective styles were measured. Multilevel moderation analysis and simple-slope analysis were applied to test the moderation of adjusting affective style in the sleep-affect association. This study found that adjusting affective style significantly moderated the association between sleep duration and subsequent positive affect. Specifically, the association between sleep duration and subsequent positive affect was positive under higher adjusting affective style and negative under extremely lower adjusting affective style. However, such moderation was not observed in associations between subsequent negative affect and sleep duration. This study uncovers the relationship between sleep duration and subsequent affect, wherein the likelihood for individuals to reach more positive affective state by increasing sleeping duration might count on their ability of emotion regulation. Additionally, negative affect cannot be downregulated simply through long sleep duration.

Investigating real-life emotions in romantic couples: a mobile EEG study

The neural basis of emotional processing has been largely investigated in constrained spatial environments such as stationary EEGs or fMRI scanners using highly artificial stimuli like standardized pictures depicting emotional scenes. Typically, such standardized experiments have low ecological validity and it remains unclear whether their results reflect neuronal processing in real-life affective situations at all. Critically, emotional situations do not only encompass the perception of emotions, but also behavioral components associated with them. In this study, we aimed to investigate real-life emotions by recording couples in their homes using mobile EEG technology during embracing, kissing and emotional speech. We focused on asymmetries in affective processing as emotions have been demonstrated to be strongly lateralized in the brain. We found higher alpha and beta power asymmetry during kissing and embracing on frontal electrodes during emotional kisses and speech compared to a neutral control condition indicative of stronger left-hemispheric activation. In contrast, we found lower alpha power asymmetry at parieto-occipital electrode sites in the emotional compared to the neutral condition indicative of stronger right-hemispheric activation. Our findings for alpha power asymmetries are in line with models of emotional lateralization that postulate a valence-specific processing over frontal cortices and right-hemispheric dominance in emotional processing in parieto-occipital regions. In contrast, beta power asymmetries pointed more towards valence-specific processing indicating that, while alpha and beta frequencies seem to be functionally associated, they are not reflecting identical cognitive processing.

The Shape of Water Stream Induces Differences in P300 and Alpha Oscillation

Touching is a fundamental human behavior used to evaluate objects in the external world. Many previous studies have used tactile stimulation to conduct psychological and psychophysiological experiments. However, most of these studies used solid material, not water stream, as an experimental stimulus. To investigate water perception, or to easily control the temperature of an experimental stimulus, it is important to be able to control the water stimulus. In this study, we investigated the usability of water as an experimental stimulus for electroencephalography (EEG) experiments and report the basic EEG response to water stimulus. We developed a tactile stimulation device using a water stream to study EEG responses, with the ability to control the stimulus onset timing. As stimuli, we selected two types of water stream, normal and soft, based on a psychological experiment to confirm a difference of subjective feeling induced by these water streams. We conducted a typical oddball task using the two different water streams and recorded EEG waveforms from 64 electrodes while participants touched the water streams. We calculated P300 at the Pz electrode, alpha asymmetry at the frontal electrodes, and alpha suppression at the parietal area. As a result, we observed typical P300 differentiation based on the stimulus proportion (target 20% and standard 80%). We observed a weaker alpha suppression when participants touched the soft water stream compared to the normal shower. These results demonstrate the usability of water stream in psychophysiological studies and suggested that alpha suppression could be a candidate to evaluate comfort of water stream.

Goal Orientations and Activation of Approach Versus Avoidance Motivation While Awaiting an Achievement Situation in the Laboratory

While some students try to give their best in an achievement situation, others show disengagement and just want to get the situation over and done with. The present study investigates the role of students' tendencies for approach or avoidance motivation while anticipating tasks and the corresponding activation of the approach/avoidance motivational system as indicated by transient changes of EEG alpha asymmetry. Overall, 62 students (50 female; age: M = 23.8, SD = 3.5) completed a goal orientation questionnaire (learning goals, performance-approach, performance-avoidance, and work avoidance). They joined a laboratory experiment where EEG was recorded during resting condition as well as when students were anticipating tasks. Standard multiple regression analysis showed that higher values on performance-avoidance were related to a higher activation of the approach system whereas higher values on work avoidance were related to a higher activation of the avoidance system. Results question present assumptions about avoidance related goal orientations.

Unihemispheric sleep and asymmetrical sleep: behavioral, neurophysiological, and functional perspectives

Sleep is a behavior characterized by a typical body posture, both eyes' closure, raised sensory threshold, distinctive electrographic signs, and a marked decrease of motor activity. In addition, sleep is a periodically necessary behavior and therefore, in the majority of animals, it involves the whole brain and body. However, certain marine mammals and species of birds show a different sleep behavior, in which one cerebral hemisphere sleeps while the other is awake. In dolphins, eared seals, and manatees, unihemispheric sleep allows them to have the benefits of sleep, breathing, thermoregulation, and vigilance. In birds, antipredation vigilance is the main function of unihemispheric sleep, but in domestic chicks, it is also associated with brain lateralization or dominance in the control of behavior. Compared to bihemispheric sleep, unihemispheric sleep would mean a reduction of the time spent sleeping and of the associated recovery processes. However, the behavior and health of aquatic mammals and birds does not seem at all impaired by the reduction of sleep. The neural mechanisms of unihemispheric sleep are unknown, but assuming that the neural structures involved in sleep in cetaceans, seals, and birds are similar to those of terrestrial mammals, it is suggested that they involve the interaction of structures of the hypothalamus, basal forebrain, and brain stem. The neural mechanisms promoting wakefulness dominate one side of the brain, while those promoting sleep predominates the other side. For cetaceans, unihemispheric sleep is the only way to sleep, while in seals and birds, unihemispheric sleep events are intermingled with bihemispheric and rapid eye movement sleep events. Electroencephalogram hemispheric asymmetries are also reported during bihemispheric sleep, at awakening, and at sleep onset, as well as being associated with a use-dependent process (local sleep).

The brain's response to pleasant touch: an EEG investigation of tactile caressing

Somatosensation as a proximal sense can have a strong impact on our attitude toward physical objects and other human beings. However, relatively little is known about how hedonic valence of touch is processed at the cortical level. Here we investigated the electrophysiological correlates of affective tactile sensation during caressing of the right forearm with pleasant and unpleasant textile fabrics. We show dissociation between more physically driven differential brain responses to the different fabrics in early somatosensory cortex - the well-known mu-suppression (10-20 Hz) - and a beta-band response (25-30 Hz) in presumably higher-order somatosensory areas in the right hemisphere that correlated well with the subjective valence of tactile caressing. Importantly, when using single trial classification techniques, beta-power significantly distinguished between pleasant and unpleasant stimulation on a single trial basis with high accuracy. Our results therefore suggest a dissociation of the sensory and affective aspects of touch in the somatosensory system and may provide features that may be used for single trial decoding of affective mental states from simple electroencephalographic measurements.

Serotonin transporter genotype (5-HTTLPR) and electrocortical responses indicating the sensitivity to negative emotional cues

Growing literature indicates that emotional reactivity and regulation are strongly linked to genetic modulation of serotonergic neurotransmission. However, until now, most studies have focused on the relationship between genotypic markers, in particular the serotonin transporter-linked polymorphic region (5-HTTLPR), and neural structures using MRI. The current study aimed to bridge the gap between the relevant MRI literature on the effects of the 5-HTTLPR genotype and the research tradition focusing on transient lateralized changes of electrocortical activity in the prefrontal cortex using electroencephalography (EEG). Lateral shifts of EEG alpha asymmetry in response to an aversive film consisting of scenes of real injury and death were assessed in healthy participants (n = 165). To evaluate the specificity of the 5-HTTLPR effect, participants were also tested for the COMT Val158Met polymorphism which is linked to dopamine inactivation. While viewing the film, individuals homozygous for the 5-HTTLPR short allele displayed a clear lateral shift of dorsolateral frontal activity to the right, which was virtually absent in participants carrying the long allele. The heightened electrocortical response to the aversive stimulation and its direction indicates a greater propensity of s/s homozygotes to experience withdrawal oriented affect in response to negative emotion cues in the environment. Moreover, together with previous research the findings support the notion of a link between the serotonergic system and self-regulation related to avoidance motivation, and a link between the dopaminergic system and self-regulation related to approach motivation.

An ensemble with the Chinese pentatonic scale using electroencephalogram from both hemispheres

To listen to brain activity as a piece of music, we previously proposed scale-free brainwave music (SFBM) technology, which translated the scalp electroencephalogram (EEG) into musical notes according to the power law of both the EEG and music. In this study, the methodology was further extended to ensemble music on two channels from the two hemispheres. EEG data from two channels symmetrically located on the left and right hemispheres were translated into MIDI sequences by SFBM, and the EEG parameters modulated the pitch, duration and volume of each note. Then, the two sequences were filtered into an ensemble with two voices: the pentatonic scale (traditional Chinese music) or the heptatonic scale (standard Western music). We demonstrated differences in harmony between the two scales generated at different sleep stages, with the pentatonic scale being more harmonious. The harmony intervals of this brain ensemble at various sleep stages followed the power law. Compared with the heptatonic scale, it was easier to distinguish the different stages using the pentatonic scale. These results suggested that the hemispheric ensemble can represent brain activity by variations in pitch, tempo and harmony. The ensemble with the pentatonic scale sounds more consonant, and partially reflects the relations of the two hemispheres. This can be used to distinguish the different states of brain activity and provide a new perspective on EEG analysis.

Preventing construction worker injury incidents through the management of personal stress and organizational stressors

Construction workers (CWs) are positioned at the lowest level of an organization and thus have limited control over their work. For this reason, they are often deprived of their due rewards and training or sometimes are even compelled to focus on production at the expense of their own safety. These organizational stressors not only cause the CWs stress but also impair their safety behaviors. The impairment of safety behaviors is the major cause of CW injury incidents. Hence, to prevent injury incidents and enhance safety behaviors of CWs, the current study aimed to identify the impact of various organizational stressors and stress on CW safety behaviors and injury incidents. To achieve this aim, we surveyed 395 CWs. Using factor analysis, we identified five organizational stressors (unfair reward and treatment, inappropriate safety equipment, provision of training, lack of goal setting, and poor physical environment), two types of stress (emotional and physical), and safety behaviors. The results of correlation and regression analyses revealed the following: (1) injury incidents were minimized by safety behaviors but escalated by a lack of goal setting, (2) safety behaviors were maximized by moderate levels of emotional stress (i.e., an inverted U-shape relationship between these two variables) and increased in line with physical stress and inappropriate safety equipment, (3) emotional stress was positively predicted by the provision of training and inappropriate safety equipment, and (4) physical stress was predicted only by inappropriate safety equipment. Based on these results, we suggest various recommendations to construction stakeholders on how to prevent CW injury incidents.