Trait And Neurobiological Correlates Of Individual Differences In Dream Recall And Dream Content

Subjective experiences during dexmedetomidine- or propofol-induced unresponsiveness and non-rapid eye movement sleep in healthy male subjects

BACKGROUND

Anaesthetic-induced unresponsiveness and non-rapid eye movement (NREM) sleep share common neural pathways and neurophysiological features. We hypothesised that these states bear resemblance also at the experiential level.

METHODS

We compared, in a within-subject design, the prevalence and content of experiences in reports obtained after anaesthetic-induced unresponsiveness and NREM sleep. Healthy males (N=39) received dexmedetomidine (n=20) or propofol (n=19) in stepwise doses to induce unresponsiveness. Those rousable were interviewed and left unstimulated, and the procedure was repeated. Finally, the anaesthetic dose was increased 50%, and the participants were interviewed after recovery. The same participants (N=37) were also later interviewed after NREM sleep awakenings.

RESULTS

Most subjects were rousable, with no difference between anaesthetic agents (P=0.480). Lower drug plasma concentrations were associated with being rousable for both dexmedetomidine (P=0.007) and propofol (P=0.002) but not with recall of experiences in either drug group (dexmedetomidine: P=0.543; propofol: P=0.460). Of the 76 and 73 interviews performed after anaesthetic-induced unresponsiveness and NREM sleep, 69.7% and 64.4% included experiences, respectively. Recall did not differ between anaesthetic-induced unresponsiveness and NREM sleep (P=0.581), or between dexmedetomidine and propofol in any of the three awakening rounds (P>0.05). Disconnected dream-like experiences (62.3% vs 51.1%; P=0.418) and memory incorporation of the research setting (88.7% vs 78.7%; P=0.204) were equally often present in anaesthesia and sleep interviews, respectively, whereas awareness, signifying connected consciousness, was rarely reported in either state.

CONCLUSIONS

Anaesthetic-induced unresponsiveness and NREM sleep are characterised by disconnected conscious experiences with corresponding recall frequencies and content.

CLINICAL TRIAL REGISTRATION

Clinical trial registration. This study was part of a larger study registered at ClinicalTrials.gov (NCT01889004).

Topographic-dynamic reorganisation model of dreams (TRoD) - A spatiotemporal approach

Dreams are one of the most bizarre and least understood states of consciousness. Bridging the gap between brain and phenomenology of (un)conscious experience, we propose the Topographic-dynamic Re-organization model of Dreams (TRoD). Topographically, dreams are characterized by a shift towards increased activity and connectivity in the default-mode network (DMN) while they are reduced in the central executive network, including the dorsolateral prefrontal cortex (except in lucid dreaming). This topographic re-organization is accompanied by dynamic changes; a shift towards slower frequencies and longer timescales. This puts dreams dynamically in an intermediate position between awake state and NREM 2/SWS sleep. TRoD proposes that the shift towards DMN and slower frequencies leads to an abnormal spatiotemporal framing of input processing including both internally- and externally-generated inputs (from body and environment). In dreams, a shift away from temporal segregation to temporal integration of inputs results in the often bizarre and highly self-centric mental contents as well as hallucinatory-like states. We conclude that topography and temporal dynamics are core features of the TroD, which may provide the connection of neural and mental activity, e.g., brain and experience during dreams as their "common currency".

An observatory on changes in dreaming during a pandemic: a living systematic review (part 1)

A 'new' way of dreaming has emerged during the pandemic, enhancing the interest of psychological literature. Indeed, during the years of the spread of coronavirus disease 2019 (COVID-19), many studies have investigated dream-related phenomena and dreaming functions. Considering the constant and rapid emergence of new results on this topic, the main aim of this study was to create an 'observatory' on the short- and long-term consequences of the COVID-19 pandemic on dreaming, by means of a living systematic review. The baseline results are presented, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement guidelines, to identify and discuss existing studies about dreams and dreaming during the COVID-19 pandemic published until February 2022. Web of Science, Embase, EBSCO, and PubMed were used for the search strategy, yielding 71 eligible papers included in the review. Our results show: (a) a more intense oneiric activity during lockdown; (b) changes in dreaming components (especially dream-recall and nightmare frequency); (c) a particular dreaming scenario ('pandemic dreams'); (d) an alteration of the dreaming-waking-life continuum and a specific function of dreaming as emotional regulator. Findings suggest that monitoring changes in dreaming provides important information about psychological health and could also contribute to the debate on the difficulties of dreaming, as well as sleeping, in particular during and after a period of 'collective trauma'.

The route to recall a dream: theoretical considerations and methodological implications

The goal of this paper is to shed new light on the relation between dream recall and dream experiences by providing a thorough analysis of the process that leads to dream reports. Three crucial steps of this process will be distinguished: dream production (the generation of a conscious experience during sleep), dream encoding (storing a trace of this experience in memory) and dream retrieval (accessing the memory trace upon awakening). The first part of the paper will assess how major theories think about the relationship between dream reports and these distinct steps. The second part will systematise how trait and state factors affecting dream recall-given different theoretical assumptions-might interact with dream production, encoding and retrieval. Understanding how the distinct steps of dream recall can be modulated by different factors is crucial for getting a better grip on how to acquire information about these steps empirically and for drawing methodological conclusions with regard to the tools dream research relies on to collect subjective data about dream experiences. The third part of the paper will analyse how laboratory reports, logs and retrospective scales interact with the different factors that affect the distinct steps leading to dream reports and will argue that prospective methods provide more direct access to data regarding dream production and encoding than retrospective methods, which-due to their inability to provide systematic control over the factors affecting the retrieval stage-screen-off the variability in the production and the encoding of dreams.

The dynamic framework of mind wandering revisited: How mindful meta-awareness affects mental states' constraints

The dynamic framework of mind wandering (Christoff, Irving, Fox, Spreng, & Andrews-Hanna, 2016) is reviewed and modified through integrating the construct of mindful meta-awareness. The dynamic framework maintains that mind wandering belongs to a family of spontaneous thought phenomena. The key defining feature of mind wandering is 'spontaneity' which characterizes the dynamic nature of thoughts in the framework. The argument is made that incorporating the mindful meta-awareness construct modifies the dynamic framework as follows: (1) the framework's criteria for mind wandering do not hold anymore as meta-awareness changes the relationship between thoughts and constraints, and (2) lucid dreaming can be categorized as unguided thought while at the same time being dependent on deliberate constraints. Finally, the application of this modified framework will be discussed in terms of the treatment of mental disorders related to spontaneous thought alterations, in particular depression and nightmares.

Dream Recall/Affect and the Hypothalamic-Pituitary-Adrenal Axis

In this concise review, we present an overview of research on dream recall/affect and of the hypothalamic–pituitary–adrenal (HPA) axis, discussing caveats regarding the action of hormones of the HPA axis (mainly cortisol and its free form, cortisol-binding globulin and glucocorticoid receptors). We present results of studies regarding dream recall/affect and the HPA axis under physiological (such as waking) or pathological conditions (such as in Cushing’s syndrome or stressful situations). Finally, we try to integrate the effect of the current COVID-19 situation with dream recall/affect vis-à-vis the HPA axis.

Changes in dream features across the first and second waves of the Covid-19 pandemic

Research during the Covid‐19 pandemic has highlighted its significant impact on dreaming. Here we address changes in dream features both during the first wave, when the Italian government imposed a total lockdown, and the second wave (autumn 2020), when a partial lockdown was effected. In April 2020 (total lockdown), 1,622 participants (M_age = 34.1 ± 13.6 years; 1171F) completed an online survey including the Pittsburgh Sleep Quality Index and a set of questions on dream features and their possible changes relative to the month preceding the lockdown (pre‐total lockdown). In November 2020 (partial lockdown), 214 participants (M_age = 36.78 ± 14.2 years; 159F) from the previous sample completed the same survey. Approximately half of the subjects reported increased or decreased dream frequency (30.5% and 21.8%), length (27.1% and 15.8%) and vividness (31.5% and 17.1%) during total lockdown as well as during partial lockdown (frequency: 30.3% and 13.5%; length: 23.3% and 12.6%; vividness: 31.6% and 24.1%). Dream affect became significantly more negative in total lockdown relative to pre‐total lockdown and in partial lockdown relative to pre‐partial lockdown (both p < .001). Both in total lockdown and partial lockdown, increased negative dream emotionality significantly predicted changes in dream frequency, length and vividness, and was significantly predicted, in turn, by worsened sleep quality. Our data confirm that dream features are significantly affected by major life changes such as those imposed by a pandemic. The fact that between lockdowns negative dream affect returned almost to baseline level suggests that dream emotionality is closely related to lifestyle and wake‐time emotional changes. Also, our findings point to a modulating role of sleep quality on dream emotionality.

Methodological Recommendations to Control for Factors Influencing Dream and Nightmare Recall in Clinical and Experimental Studies of Dreaming

In order to ensure robust relationships between the dependent and independent variables in clinical dream/nightmare studies, the major factors which influence the frequency of reported dreams must be controlled. This article sets out methodological recommendations to both researchers seeking to ensure the equivalence of experimental groups of participants in group-matching designs, and to clinicians who wish to check that any change in frequency of reported nightmares over the course of a psychological or a pharmacological intervention is not caused by factors other than the experimental treatment itself. The main factors influencing the frequency of dream recall are presented: demographic variables, psychological characteristics, pathological dimensions, and substance consumption. A series of questionnaires is proposed for easily measuring these control variables.

Sexual dream and family relationships in frequent sexual dreamers and healthy volunteers

Early life family relationships affect the sexuality in adulthood, and these influences might be reflected in sexual dreams. The present study was designed to investigate the exact associations between family relationships and sexual dream experience. We therefore invited 62 frequent sexual dreamers (dreamers) and 104 healthy volunteers (controls) to answer the Sexual Dream Experience Questionnaire (SDEQ) and the Family Relationship Questionnaire (FRQ). Compared to controls, dreamers scored higher on all SDEQ factors and sexual dream frequency, higher on FRQ Paternal Abuse, and lower on FRQ General Attachment and Maternal Freedom Release. In controls, Paternal Abuse was associated with Joyfulness, Maternal Dominance with Aversion, and Maternal Abuse with dream frequency (-). In dreamers, Paternal Abuse was associated with Aversion, Bizarreness and dream frequency, and Maternal Freedom Release with Aversion (-). In conclusion, there were pronounced associations between sexual dreams and family relationships in frequent sexual dreamers. Paternal Abuse in particular was associated with sexual dream experience. Adverse family relationships might induce frequent sexual dream occurrence, and family therapy or early intervention of Paternal Abuse might alleviate the negative sexual dream experience.

Predicting the affective tone of everyday dreams: A prospective study of state and trait variables

Although emotions are reported in a large majority of dreams, little is known about the factors that account for night-to-night and person-to-person variations in people’s experience of dream affect. We investigated the relationship between waking trait and state variables and dream affect by testing multilevel models intended to predict the affective valence of people’s everyday dreams. Participants from the general population completed measures of personality and trauma history followed by a three-week daily journal in which they noted dream recall, valence of dreamed emotions and level of perceived stress for the day as well as prior to sleep onset. Within-subject effects accounted for most of the explained variance in the reported valence of dream affect. Trait anxiety was the only variable that significantly predicted dream emotional valence at the between-subjects level. In addition to highlighting the need for more fine-grained measures in this area of research, our results point to methodological limitations and biases associated with retrospective estimates of general dream affect and bring into focus state variables that may best explain observed within-subject variance in emotions experienced in everyday dreams.

Dream Recall and Content versus the Menstrual Cycle: A Cross-Sectional Study in Healthy Women

The association between sleep and the menstrual cycle has been scarcely studied. This study aimed to investigate the association between dream recall and content and the menstrual cycle among a large sample of young women. To this aim, 944 women were asked about their day of menstrual cycle, whether they remembered the previous night’s dreams and if they did so to describe the dream content as pleasant or unpleasant. A total of 378 women recalled the previous nights’ dreams, with 199 reporting pleasant dream affect/content and 179 reporting unpleasant dream content. In women who recalled their dreams, there was an association of pleasant dream content with the luteal phase (p = 0.038). In conclusion, in women, the hormonal milieu of the luteal phase may influence dream content.

A Novel Approach to Dream Content Analysis Reveals Links Between Learning-Related Dream Incorporation and Cognitive Abilities

Can dreams reveal insight into our cognitive abilities and aptitudes (i.e., "human intelligence")? The relationship between dream production and trait-like cognitive abilities is the foundation of several long-standing theories on the neurocognitive and cognitive-psychological basis of dreaming. However, direct experimental evidence is sparse and remains contentious. On the other hand, recent research has provided compelling evidence demonstrating a link between dream content and new learning, suggesting that dreams reflect memory processing during sleep. It remains to be investigated whether the extent of learning-related dream incorporation (i.e., the semantic similarity between waking experiences and dream content) is related to inter-individual differences in cognitive abilities. The relationship between pre-post sleep memory performance improvements and learning-related dream incorporation was investigated (N = 24) to determine if this relationship could be explained by inter-individual differences in intellectual abilities (e.g., reasoning, short term memory (STM), and verbal abilities). The extent of dream incorporation using a novel and objective method of dream content analysis, employed a computational linguistic approach to measure the semantic relatedness between verbal reports describing the experience on a spatial (e.g., maze navigation) or a motor memory task (e.g., tennis simulator) with subsequent hypnagogic reverie dream reports and waking "daydream" reports, obtained during a daytime nap opportunity. Consistent with previous studies, the extent to which something new was learned was related (r = 0.47) to how richly these novel experiences were incorporated into the content of dreams. This was significant for early (the first 4 dream reports) but not late dreams (the last 4 dream reports). Notably, here, we show for the first time that the extent of this incorporation for early dreams was related (r = 0.41) to inter-individual differences in reasoning abilities. On the other hand, late dream incorporation was related (r = 0.46) to inter-individual differences in verbal abilities. There was no relationship between performance improvements and intellectual abilities, and thus, inter-individual differences in cognitive abilities did not mediate the relationship between performance improvements and dream incorporation; suggesting a direct relationship between reasoning abilities and dream incorporation. This study provides the first evidence that learning-related dream production is related to inter-individual differences in cognitive abilities.

Characteristics of the memory sources of dreams: A new version of the content-matching paradigm to take mundane and remote memories into account

Several studies have demonstrated that dream content is related to the waking life of the dreamer. However, the characteristics of the memory sources incorporated into dreams are still unclear. We designed a new protocol to investigate remote memories and memories of trivial experiences, both relatively unexplored in dream content until now. Upon awakening, for 7 days, participants identified the waking life elements (WLEs) related to their dream content and characterized them and their dream content on several scales to assess notably emotional valence. Thanks to this procedure, they could report WLEs from the whole lifespan, and mundane ones before they had been forgotten. Participants (N = 40, 14 males, age = 25.2 ± 7.6) reported 6.2 ± 2.0 dreams on average. For each participant, 83.4% ± 17.8 of the dream reports were related to one or more WLEs. Among all the WLEs incorporated into dreams dated by the participants (79.3 ± 19%), 40.2 ± 30% happened the day before the dream, 26.1 ± 26% the month before (the day before excluded), 15.8 ± 21% the year before the dream (the month before excluded), and 17.9 ± 24% happened more than one year before the dream. As could be expected from previous studies, the majority of the WLEs incorporated into dreams were scored as important by the dreamers. However, this was not true for incorporated WLEs dating from the day before the dream. In agreement with Freud's observations, the majority of the day residues were scored as mundane. Finally, for both positive and negative WLEs incorporated into dreams, the dreamt version of the WLE was rated as emotionally less intense than the original WLE. This result, showing that dreams tend to attenuate the emotional tone of waking-life memories towards a more neutral one, argues in favor of the emotional regulation hypothesis of dreaming.

Is dream recall underestimated by retrospective measures and enhanced by keeping a logbook? An empirical investigation

In a recent review, Aspy, Delfabbro, and Proeve (2015) highlighted the tendency for retrospective measures of dream recall to yield substantially lower recall rates than logbook measures, a phenomenon they termed the retrospective-logbook disparity. One explanation for this phenomenon is that retrospective measures underestimate true dream recall. Another explanation is that keeping a logbook tends to enhance dream recall. The present study provides a thorough empirical investigation into the retrospective-logbook disparity using a range of retrospective and logbook measures and three different types of logbook. Retrospective-logbook disparities were correlated with a range of variables theoretically related to the retrospective underestimation effect, and retrospective-logbook disparities were greater among participants that reported improved dream recall during the logbook period. These findings indicate that dream recall is underestimated by retrospective measures and enhanced by keeping a logbook. Recommendations for the use of retrospective and logbook measures of dream recall are provided.

Dreaming and personality: Wake-dream continuity, thought suppression, and the Big Five Inventory

Studies have found relationships between dream content and personality traits, but there are still many traits that have been underexplored or have had questionable conclusions drawn about them. Experimental work has found a 'rebound' effect in dreams when thoughts are suppressed prior to sleep, but the effect of trait thought suppression on dream content has not yet been researched. In the present study participants (N=106) reported their Most Recent Dream, answered questions about the content of the dream, and completed questionnaires measuring trait thought suppression and the 'Big Five' personality traits. Of these, 83 were suitably recent for analyses. A significant positive correlation was found between trait thought suppression and participants' ratings of dreaming of waking-life emotions, and high suppressors reported dreaming more of their waking-life emotions than low suppressors did. The results may lend support to the compensation theory of dreams, and/or the ironic process theory of mental control.

Evidence that non-dreamers do dream: a REM sleep behaviour disorder model

To determine whether non-dreamers do not produce dreams or do not recall them, subjects were identified with no dream recall with dreamlike behaviours during rapid eye movement sleep behaviour disorder, which is typically characterised by dream-enacting behaviours congruent with sleep mentation. All consecutive patients with idiopathic rapid eye movement sleep behaviour disorder or rapid eye movement sleep behaviour disorder associated with Parkinson's disease who underwent a video-polysomnography were interviewed regarding the presence or absence of dream recall, retrospectively or upon spontaneous arousals. The patients with no dream recall for at least 10 years, and never-ever recallers were compared with dream recallers with rapid eye movement sleep behaviour disorder regarding their clinical, cognitive and sleep features. Of the 289 patients with rapid eye movement sleep behaviour disorder, eight (2.8%) patients had no dream recall, including four (1.4%) patients who had never ever recalled dreams, and four patients who had no dream recall for 10-56 years. All non-recallers exhibited, daily or almost nightly, several complex, scenic and dreamlike behaviours and speeches, which were also observed during rapid eye movement sleep on video-polysomnography (arguing, fighting and speaking). They did not recall a dream following sudden awakenings from rapid eye movement sleep. These eight non-recallers with rapid eye movement sleep behaviour disorder did not differ in terms of cognition, clinical, treatment or sleep measures from the 17 dreamers with rapid eye movement sleep behaviour disorder matched for age, sex and disease. The scenic dreamlike behaviours reported and observed during rapid eye movement sleep in the rare non-recallers with rapid eye movement sleep behaviour disorder (even in the never-ever recallers) provide strong evidence that non-recallers produce dreams, but do not recall them. Rapid eye movement sleep behaviour disorder provides a new model to evaluate cognitive processing during dreaming and subsequent recall.

The Cognitive Social Network in Dreams: Transitivity, Assortativity, and Giant Component Proportion Are Monotonic

For five individuals, a social network was constructed from a series of his or her dreams. Three important network measures were calculated for each network: transitivity, assortativity, and giant component proportion. These were monotonically related; over the five networks as transitivity increased, assortativity increased and giant component proportion decreased. The relations indicate that characters appear in dreams systematically. Systematicity likely arises from the dreamer's memory of people and their relations, which is from the dreamer's cognitive social network. But the dream social network is not a copy of the cognitive social network. Waking life social networks tend to have positive assortativity; that is, people tend to be connected to others with similar connectivity. Instead, in our sample of dream social networks assortativity is more often negative or near 0, as in online social networks. We show that if characters appear via a random walk, negative assortativity can result, particularly if the random walk is biased as suggested by remote associations.

Is dream recall underestimated by retrospective measures and enhanced by keeping a logbook? A review

There are two methods commonly used to measure dream recall in the home setting. The retrospective method involves asking participants to estimate their dream recall in response to a single question and the logbook method involves keeping a daily record of one's dream recall. Until recently, the implicit assumption has been that these measures are largely equivalent. However, this is challenged by the tendency for retrospective measures to yield significantly lower dream recall rates than logbooks. A common explanation for this is that retrospective measures underestimate dream recall. Another is that keeping a logbook enhances it. If retrospective measures underestimate dream recall and if logbooks enhance it they are both unlikely to reflect typical dream recall rates and may be confounded with variables associated with the underestimation and enhancement effects. To date, this issue has received insufficient attention. The present review addresses this gap in the literature.

Resting brain activity varies with dream recall frequency between subjects

Dreaming is still poorly understood. Notably, its cerebral underpinning remains unclear. Neuropsychological studies have shown that lesions in the temporoparietal junction (TPJ) and/or the white matter of the medial prefrontal cortex (MPFC) lead to the global cessation of dream reports, suggesting that these regions of the default mode network have key roles in the dreaming process (forebrain 'dream-on' hypothesis). To test this hypothesis, we measured regional cerebral blood flow (rCBF) using [(15)O]H2O positron emission tomography in healthy subjects with high and low dream recall frequencies (DRFs) during wakefulness (rest) and sleep (rapid eye movement (REM) sleep, N2, and N3). Compared with Low recallers (0.5 ± 0.3 dream recall per week in average), High recallers (5.2 ± 1.4) showed higher rCBF in the TPJ during REM sleep, N3, and wakefulness, and in the MPFC during REM sleep and wakefulness. We demonstrate that the resting states of High recallers and Low recallers differ during sleep and wakefulness. It coheres with previous ERP results and confirms that a high/low DRF is associated with a specific functional organization of the brain. These results support the forebrain 'dream-on' hypothesis and suggest that TPJ and MPFC are not only involved in dream recall during wakefulness but also have a role in dreaming during sleep (production and/or encoding). Increased activity in the TPJ and MPFC might promote the mental imagery and/or memory encoding of dreams. Notably, increased activity in TPJ might facilitate attention orienting toward external stimuli and promote intrasleep wakefulness, facilitating the encoding of the dreams in memory.

Dreams are made of memories, but maybe not for memory

Llewellyn's claim that rapid eye movement (REM) dream imagery may be related to the processes involved in memory consolidation during sleep is plausible. However, whereas there is voluntary and deliberate intention behind the construction of images in the ancient art of memory (AAOM) method, there is a lack of intentionality in producing dream images. The memory for dreams is also fragile, and dependent on encoding once awake.

Dream recall frequency: impact of prospective measures and motivational factors

Significant individual differences exist in dream recall frequency (DRF) but some variance is likely attributable to instrument choice in measuring DRF. Three hundred and fifty eight participants estimated their weekly DRF and recorded their dreams in either a narrative log (n = 165) or checklist log (n = 193) for 2-5 weeks. There was an early peak in DRF within the first week of both types of prospective logs after which DRF remained relatively stable. Although the two groups did not differ in their estimated DRF, significantly fewer dreams were reported per week on the narrative logs and only checklist logs yielded significantly higher DRF than participants' questionnaire estimates. The interactions between DRF measures did not vary across groups with low, medium or high baseline levels of DRF. Keeping a dream log does not necessarily increase DRF and narrative logs' time consuming nature can impact subjects' motivation to report all of their dreams over time.

Experimental research on dreaming: state of the art and neuropsychoanalytic perspectives

Dreaming is still a mystery of human cognition, although it has been studied experimentally for more than a century. Experimental psychology first investigated dream content and frequency. The neuroscientific approach to dreaming arose at the end of the 1950s and soon proposed a physiological substrate of dreaming: rapid eye movement sleep. Fifty years later, this hypothesis was challenged because it could not explain all of the characteristics of dream reports. Therefore, the neurophysiological correlates of dreaming are still unclear, and many questions remain unresolved. Do the representations that constitute the dream emerge randomly from the brain, or do they surface according to certain parameters? Is the organization of the dream's representations chaotic or is it determined by rules? Does dreaming have a meaning? What is/are the function(s) of dreaming? Psychoanalysis provides hypotheses to address these questions. Until now, these hypotheses have received minimal attention in cognitive neuroscience, but the recent development of neuropsychoanalysis brings new hopes of interaction between the two fields. Considering the psychoanalytical perspective in cognitive neuroscience would provide new directions and leads for dream research and would help to achieve a comprehensive understanding of dreaming. Notably, several subjective issues at the core of the psychoanalytic approach, such as the concept of personal meaning, the concept of unconscious episodic memory and the subject's history, are not addressed or considered in cognitive neuroscience. This paper argues that the focus on singularity and personal meaning in psychoanalysis is needed to successfully address these issues in cognitive neuroscience and to progress in the understanding of dreaming and the psyche.