Free-viewing gaze patterns reveal a mood-congruency bias in MDD during an affective fMRI/eye-tracking task

Major depressive disorder (MDD) has been related to abnormal amygdala activity during emotional face processing. However, a recent large-scale study (n = 28,638) found no such correlation, which is probably due to the low precision of fMRI measurements. To address this issue, we used simultaneous fMRI and eye-tracking measurements during a commonly employed emotional face recognition task. Eye-tracking provide high-precision data, which can be used to enrich and potentially stabilize fMRI readouts. With the behavioral response, we additionally divided the active task period into a task-related and a free-viewing phase to explore the gaze patterns of MDD patients and healthy controls (HC) and compare their respective neural correlates. Our analysis showed that a mood-congruency attentional bias could be detected in MDD compared to healthy controls during the free-viewing phase but without parallel amygdala disruption. Moreover, the neural correlates of gaze patterns reflected more prefrontal fMRI activity in the free-viewing than the task-related phase. Taken together, spontaneous emotional processing in free viewing might lead to a more pronounced mood-congruency bias in MDD, which indicates that combined fMRI with eye-tracking measurement could be beneficial for our understanding of the underlying psychopathology of MDD in different emotional processing phases.Trial Registration: The BeCOME study is registered on ClinicalTrials (gov: NCT03984084) by the Max Planck Institute of Psychiatry in Munich, Germany.

Assessing hypo-arousal during reward anticipation with pupillometry in patients with major depressive disorder: replication and correlations with anhedonia

Major depressive disorder (MDD) is a devastating and heterogenous disorder for which there are no approved biomarkers in clinical practice. We recently identified anticipatory hypo-arousal indexed by pupil responses as a candidate mechanism subserving depression symptomatology. Here, we conducted a replication and extension study of these findings. We analyzed a replication sample of 40 unmedicated patients with a diagnosis of depression and 30 healthy control participants, who performed a reward anticipation task while pupil responses were measured. Using a Bayesian modelling approach taking measurement uncertainty into account, we could show that the negative correlation between pupil dilation and symptom load during reward anticipation is replicable within MDD patients, albeit with a lower effect size. Furthermore, with the combined sample of 136 participants (81 unmedicated depressed and 55 healthy control participants), we further showed that reduced pupil dilation in anticipation of reward is inversely associated with anhedonia items of the Beck Depression Inventory in particular. Moreover, using simultaneous fMRI, particularly the right anterior insula as part of the salience network was negatively correlated with depressive symptom load in general and anhedonia items specifically. The present study supports the utility of pupillometry in assessing noradrenergically mediated hypo-arousal during reward anticipation in MDD, a physiological process that appears to subserve anhedonia.

Data-Driven Pupil Response Profiles as Transdiagnostic Readouts for the Detection of Neurocognitive Functioning in Affective and Anxiety Disorders

BACKGROUND

Neurocognitive functioning is a relevant transdiagnostic dimension in psychiatry. As pupil size dynamics track cognitive load during a working memory task, we aimed to explore if this parameter allows identification of psychophysiological subtypes in healthy participants and patients with affective and anxiety disorders.

METHODS

Our sample consisted of 226 participants who completed the n-back task during simultaneous functional magnetic resonance imaging and pupillometry measurements. We used latent class growth modeling to identify clusters based on pupil size in response to cognitive load. In a second step, these clusters were compared on affective and anxiety symptom levels, performance in neurocognitive tests, and functional magnetic resonance imaging activity.

RESULTS

The clustering analysis resulted in two distinct pupil response profiles: one with a stepwise increasing pupil size with increasing cognitive load (reactive group) and one with a constant pupil size across conditions (nonreactive group). A larger increase in pupil size was significantly associated with better performance in neurocognitive tests in executive functioning and sustained attention. Statistical maps of parametric modulation of pupil size during the n-back task showed the frontoparietal network in the positive contrast and the default mode network in the negative contrast. The pupil response profile of the reactive group was associated with more thalamic activity, likely reflecting better arousal upregulation and less deactivation of the limbic system.

CONCLUSIONS

Pupil measurements have the potential to serve as a highly sensitive psychophysiological readout for detection of neurocognitive deficits in the core domain of executive functioning, adding to the development of valid transdiagnostic constructs in psychiatry.

Startle Latency as a Potential Marker for Amygdala-Mediated Hyperarousal

BACKGROUND

Fear-related disorders are characterized by hyperexcitability in reflexive circuits and maladaptive associative learning mechanisms. The startle reflex is suited to investigate both processes, either by probing it under baseline conditions or by deriving it in fear conditioning studies. In anxiety research, the amplitude of the fear-potentiated startle has been shown to be influenced by amygdalar circuits and has typically been the readout of interest. In schizophrenia research, prolonged startle peak latency under neutral conditions is an established readout, thought to reflect impaired processing speed. We therefore explored whether startle latency is an informative readout for human anxiety research.

METHODS

We investigated potential similarities and differences of startle peak latency and amplitude derived from a classical fear conditioning task in a sample of 206 participants with varying severity levels of anxiety disorders and healthy control subjects. We first reduced startle response to stable components and regressed individual amygdala gray matter volumes onto the resulting startle measures. We then probed time, stimulus, and group effects of startle latency.

RESULTS

We showed that startle latency and startle amplitude were 2 largely uncorrelated measures; startle latency, but not amplitude, showed a sex-specific association with gray matter volume of the amygdala; startle latencies showed a fear-dependent task modulation; and patients with fear-related disorders displayed shorter startle latencies throughout the fear learning task.

CONCLUSIONS

These data provide support for the notion that probing startle latencies under threat may engage amygdala-modulated threat processing, making them a complementary marker for human anxiety research.

Facing Your Fear in Immersive Virtual Reality: Avoidance Behavior in Specific Phobia

Specific phobias are the most common anxiety disorder and are characterized by avoidance behavior. Avoidance behavior impacts daily function and is proposed to impair extinction learning. However, despite its prevalence, its objective assessment remains a challenge. To this end, we developed a fully automated experimental procedure using immersive virtual reality. The procedure contained a behavioral search, forced-choice, and an approach task with varying degrees of freedom and task relevance of the stimuli. In this study, we examined the sensitivity and feasibility of these tasks to assess avoidance behavior in patients with specific phobia. We adapted the tasks by replacing the originally conditioned stimuli with a spider and a neutral animal and investigated 31 female participants composed of 15 spider-phobic and 16 non-phobic participants. As the non-phobics were quite heterogeneous in terms of their Fear of Spiders Questionnaire (FSQ) scores, we subdivided them into six “fearfuls” that had elevated FSQ scores, and 10 “non-fearfuls” that had no fear of spiders. The phobics successfully managed to complete the procedure and showed consistent avoidance behavior across all behavioral tasks. Compared to the non-fearfuls, which did not show any avoidance behavior at all, the phobics looked at the spider much more often and clearly directed their body toward it in the search task. In the approach task, they hesitated most when they were close to the spider, and their difficulty to touch the spider was reflected in a strong increase in right hand acceleration changes. The fearfuls showed avoidance behavior depending on the tasks: strongest in the search task and weakest in the approach task. Additionally, we identified subjective valence ratings of the spider as the main influence on both objective avoidance behavior and subjective well-being after exposure, mediating the effect of the FSQ. In summary, the behavioral tasks are well suited to assess avoidance behavior in phobic participants and provide detailed insights into the process of avoidance.

Pupillometry tracks cognitive load and salience network activity in a working memory functional magnetic resonance imaging task

The diameter of the human pupil tracks working memory processing and is associated with activity in the frontoparietal network. At the same time, recent neuroimaging research has linked human pupil fluctuations to activity in the salience network. In this combined functional magnetic resonance imaging (fMRI)/pupillometry study, we recorded the pupil size of healthy human participants while they performed a blockwise organized working memory task (N‐back) inside an MRI scanner in order to monitor the pupil fluctuations associated neural activity during working memory processing. We first confirmed that mean pupil size closely followed working memory load. Combining this with fMRI data, we focused on blood oxygen level dependent (BOLD) correlates of mean pupil size modeled onto the task blocks as a parametric modulation. Interrogating this modulated task regressor, we were able to retrieve the frontoparietal network. Next, to fully exploit the within‐block dynamics, we divided the blocks into 1 s time bins and filled these with corresponding pupil change values (first‐order derivative of pupil size). We found that pupil change within N‐back blocks was positively correlated with BOLD amplitudes in the areas of the salience network (namely bilateral insula, and anterior cingulate cortex). Taken together, fMRI with simultaneous measurement of pupil parameters constitutes a valuable tool to dissect working memory subprocesses related to both working memory load and salience of the presented stimuli.

Examining Differences in Fear Learning in Patients With Obsessive-Compulsive Disorder With Pupillometry, Startle Electromyography and Skin Conductance Responses

Obsessive-compulsive disorder (OCD) is characterized by recurrent, persistent thoughts and repetitive behaviors causing stress and anxiety. In the associative learning model of OCD, mechanisms of fear extinction are supposed to partly underlie symptom development, maintenance and treatment of OCD, proposing that OCD patients suffer from rigid memory associations and inhibitory learning deficits. To test these assumptions, previous studies have used skin conductance and subjective ratings as readouts in fear conditioning paradigms, finding impaired fear extinction learning, impaired fear extinction recall or no differences between individuals with OCD and healthy controls. Against this heterogeneous background, we tested fear acquisition and extinction in 37 OCD patients and 56 healthy controls, employing skin conductance as well as pupillometry and startle electromyography. Extinction recall was also included in a subsample. We did not observe differences between groups in any of the task phases, except a trend toward higher startle amplitudes during extinction for OCD. Overall, sensitive readouts such as pupillometry and startle responses did not provide evidence for moderate-to-large inhibitory learning deficits using classical fear conditioning, challenging the assumption of generically impaired extinction learning and memory in OCD.

Pupil Dilation during Reward Anticipation Is Correlated to Depressive Symptom Load in Patients with Major Depressive Disorder

Depression is a debilitating disorder with high prevalence and socioeconomic cost, but the brain-physiological processes that are altered during depressive states are not well understood. Here, we build on recent findings in macaques that indicate a direct causal relationship between pupil dilation and anterior cingulate cortex mediated arousal during anticipation of reward. We translated these findings to human subjects with concomitant pupillometry/fMRI in a sample of unmedicated participants diagnosed with major depression and healthy controls. We could show that the upregulation and maintenance of arousal in anticipation of reward was disrupted in patients in a symptom-load dependent manner. We could further show that the failure to maintain reward anticipatory arousal showed state-marker properties, as it tracked the load and impact of depressive symptoms independent of prior diagnosis status. Further, group differences of anticipatory arousal and continuous correlations with symptom load were not traceable only at the level of pupillometric responses, but were mirrored also at the neural level within salience network hubs. The upregulation and maintenance of arousal during reward anticipation is a novel translational and well-traceable process that could prove a promising gateway to a physiologically informed patient stratification and targeted interventions.

Quantifying Human Avoidance Behavior in Immersive Virtual Reality

Avoidance behavior is a key symptom of most anxiety disorders and a central readout in animal research. However, the quantification of real-life avoidance behavior in humans is typically restricted to clinical populations, who show actual avoidance of phobic objects. In experimental approaches for healthy participants, many avoidance tasks utilize button responses or a joystick navigation on the screen as indicators of avoidance behavior. To allow the ecologically valid assessment of avoidance behavior in healthy participants, we developed a new automated immersive Virtual Reality paradigm, where participants could freely navigate in virtual 3-dimensional, 360-degrees scenes by real naturalistic body movements. A differential fear conditioning procedure was followed by three newly developed behavioral tasks to assess participants’ avoidance behavior of the conditioned stimuli: an approach, a forced-choice, and a search task. They varied in instructions, degrees of freedom, and high or low task-related relevance of the stimuli. We initially examined the tasks in a quasi-experiment (N = 55), with four consecutive runs and various experimental adaptations. Here, although we observed avoidance behavior in all three tasks after additional reinforcement, we only detected fear-conditioned avoidance behavior in the behavioral forced-choice and search tasks. These findings were largely replicated in a confirmatory experiment (N = 72) with randomized group allocation, except that fear-conditioned avoidance behavior was only manifest in the behavioral search task. This supports the notion that the behavioral search task is sensitive to detect avoidance behavior after fear conditioning only, whereas the behavioral approach and forced-choice tasks are still able to detect “strong” avoidance behavior after fear conditioning and additional reinforcement.

The biological classification of mental disorders (BeCOME) study: a protocol for an observational deep-phenotyping study for the identification of biological subtypes

BACKGROUND

A major research finding in the field of Biological Psychiatry is that symptom-based categories of mental disorders map poorly onto dysfunctions in brain circuits or neurobiological pathways. Many of the identified (neuro) biological dysfunctions are "transdiagnostic", meaning that they do not reflect diagnostic boundaries but are shared by different ICD/DSM diagnoses. The compromised biological validity of the current classification system for mental disorders impedes rather than supports the development of treatments that not only target symptoms but also the underlying pathophysiological mechanisms. The Biological Classification of Mental Disorders (BeCOME) study aims to identify biology-based classes of mental disorders that improve the translation of novel biomedical findings into tailored clinical applications.

METHODS

BeCOME intends to include at least 1000 individuals with a broad spectrum of affective, anxiety and stress-related mental disorders as well as 500 individuals unaffected by mental disorders. After a screening visit, all participants undergo in-depth phenotyping procedures and omics assessments on two consecutive days. Several validated paradigms (e.g., fear conditioning, reward anticipation, imaging stress test, social reward learning task) are applied to stimulate a response in a basic system of human functioning (e.g., acute threat response, reward processing, stress response or social reward learning) that plays a key role in the development of affective, anxiety and stress-related mental disorders. The response to this stimulation is then read out across multiple levels. Assessments comprise genetic, molecular, cellular, physiological, neuroimaging, neurocognitive, psychophysiological and psychometric measurements. The multilevel information collected in BeCOME will be used to identify data-driven biologically-informed categories of mental disorders using cluster analytical techniques.

DISCUSSION

The novelty of BeCOME lies in the dynamic in-depth phenotyping and omics characterization of individuals with mental disorders from the depression and anxiety spectrum of varying severity. We believe that such biology-based subclasses of mental disorders will serve as better treatment targets than purely symptom-based disease entities, and help in tailoring the right treatment to the individual patient suffering from a mental disorder. BeCOME has the potential to contribute to a novel taxonomy of mental disorders that integrates the underlying pathomechanisms into diagnoses.

TRIAL REGISTRATION

Retrospectively registered on June 12, 2019 on ClinicalTrials.gov (TRN: NCT03984084).

Neural Processing During Fear Extinction Predicts Intrusive Memories

BACKGROUND

Deficient extinction learning has been suggested as an important mechanism involved in the etiology of posttraumatic stress disorder. A key feature of posttraumatic stress disorder, reexperiencing the trauma in form of intrusions, may be linked to deficient extinction learning. This link is investigated in a novel, functional magnetic resonance imaging-compatible fear conditioning procedure that uses trauma films. Based on previous results, we expected deficient fear extinction indexed by exaggerated responding in the anterior insula and dorsal anterior cingulate cortex to predict subsequent intrusions.

METHODS

A total of 58 healthy participants underwent acquisition and extinction learning with faces as conditioned stimuli (CS) and highly aversive 16-second films depicting interpersonal violence as unconditioned stimuli. During the subsequent 3 days, participants reported intrusive memories on their smartphone.

RESULTS

Successful fear acquisition was evidenced by differential (CS+ > CS-) activity (threat cues associated with trauma films > cues paired only with neutral films) of a widespread network, including the anterior insula and dorsal anterior cingulate cortex, whereas extinction was characterized exclusively by differential anterior insula activity. Differential conditioned responding during late extinction in the anterior insula and dorsal anterior cingulate cortex was positively related to intrusive memory frequency independent of unconditioned stimuli responding. Exploratory analysis also revealed intrusion sensitivity of the hippocampus, rostral anterior cingulate cortex, and ventromedial prefrontal cortex, among others.

CONCLUSIONS

Results support the role of extinction learning in intrusive memory formation; a failure to uncouple conditioned emotional responding from external threat cues was associated with subsequent intrusive memories, representing a potential risk marker for developing posttraumatic stress disorder symptomatology after trauma.

Hyperarousal captured in increased number of arousal events during pre-REM periods in individuals with frequent nightmares

The aim of this study was to investigate hyperarousal in individuals with frequent nightmares (NM participants) by calculating arousal events during nocturnal sleep. We hypothesized an increased number of arousals in NM participants compared with controls, especially during those periods where the probability of spontaneous arousal occurrence is already high, such as non-rapid eye movement to rapid eye movement transitions (pre-rapid eye movement periods). Twenty-two NM participants and 23 control participants spent two consecutive nights in our sleep laboratory, monitored by polysomnography. Arousal number and arousal length were calculated only for the second night, for 10 min before rapid eye movement (pre-rapid eye movement) and 10 min after rapid eye movement (post-rapid eye movement) periods, as well as non-rapid eye movement and rapid eye movement phases separately. Repeated-measures ANOVA model testing revealed significant Group (NM participants, controls) × Phase (pre-rapid eye movement, post-rapid eye movement) interaction in case of the number of arousals. Furthermore, post hoc analysis showed a significantly increased number of arousals during pre-rapid eye movement periods in NM participants, compared with controls, a difference that disappeared in post-rapid eye movement periods. We propose that focusing the analyses of arousals specifically on state transitory periods offers a unique perspective into the fragile balance between the sleep-promoting and arousal systems. This outlook revealed an increased number of arousals in NM participants, reflecting hyperarousal during pre-rapid eye movement periods.

Cortical hyperarousal in NREM sleep normalizes from pre- to post- REM periods in individuals with frequent nightmares

Study Objectives

Frequent nightmares have a high prevalence and constitute a risk factor for psychiatric conditions, but their pathophysiology is poorly understood. Our aim was to examine sleep architecture and electroencephalographic markers—with a specific focus on state transitions—related to sleep regulation and hyperarousal in participants with frequent nightmares (NM participants) versus healthy controls.

Methods

Healthy controls and NM participants spent two consecutive nights in the sleep laboratory. Second night spectral power during NREM to REM sleep (pre-REM) and REM to NREM (post-REM) transitions as well as during NREM and REM periods were evaluated for 22 NM participants compared to 22 healthy controls with a similar distribution of age, gender, and dream recall frequency.

Results

We found significant differences between the groups in the pre-REM to post-REM changes in low- and high-frequency domains. NM participants experienced a lower amount of slow-wave sleep and showed increased beta and gamma power during NREM and pre-REM periods. No difference was present during REM and post-REM phases. Furthermore, while increased pre-REM high-frequency power seems to be mainly driven by post-traumatic stress disorder (PTSD) symptom intensity, decreased low-frequency activity occurred regardless of PTSD symptom severity.

Conclusion

Our findings indicate that NM participants had increased high-frequency spectral power during NREM and pre-REM periods, as well as relatively reduced slow frequency and increased fast frequency spectral power across pre-and post-REM periods. This combination of reduced sleep-protective activity and increased hyperarousal suggests an imbalance between sleep regulatory and wake-promoting systems in NM participants.

Human Memories Can Be Linked by Temporal Proximity

Real-world memories involve the integration of multiple events across time, yet the mechanisms underlying this integration is unknown. Recent rodent studies show that distinct memories encoded within a few hours, but not several days, share a common neural ensemble, and a common fate whereby later fear conditioning can transfer from one memory to the other. Here, we tested if distinct memories could be linked by temporal proximity in humans. 74 young adults encoded two memories (A and B) close (3-h) or far apart (7-day) in time. One day after encoding the second memory (B), Memory A was updated by pairing it with electric shock (i.e., fear conditioning). We tested whether the memory and fear associated with Memory B would be stronger in the 3-h, compared with the 7-day condition. Results were generally consistent with rodent studies, where we found heightened Memory B fear expression when the two memories were encoded close, but not far apart, in time. Furthermore, there was less forgetting of Memory B in the 3-h compared to 7-day condition. Our results suggest that temporally proximal memories may be linked, such that updating one experience updates the other.

Peritraumatic Neural Processing and Intrusive Memories: The Role of Lifetime Adversity

BACKGROUND

Pathological peritraumatic encoding is proposed as a proximal risk factor for the development of posttraumatic stress disorder (PTSD), with trauma-analog studies linking increased neural processing of trauma films to intrusive trauma recollections, a core symptom of PTSD. Cumulative lifetime adversity is proposed as a more distal risk factor, with research indicating a tipping point at about five events with regard to PTSD development following re-exposure to trauma. Thus, within a diathesis × stress framework, increased peritraumatic neural processing may constitute a specific risk factor for PTSD, particularly in individuals with several lifetime adversities.

METHODS

Fifty-three healthy women watched highly aversive films depicting severe interpersonal violence versus neutral films during functional magnetic resonance imaging, and they reported involuntary recollections during subsequent days. Moderation analyses tested the interactive relationship between peritraumatic neural processing and lifetime adversity in predicting intrusion load, i.e., the total number of intrusions weighted for their average distress.

RESULTS

Increased processing of aversive versus neutral films in the amygdala, anterior insula, dorsal and rostral anterior cingulate cortices, and hippocampus predicted increased intrusion load only in participants reporting above five lifetime adversities; for participants reporting few to none, no such relationship was found. This interactive relationship explained ≤59% of variance. Conditioned stimuli preceding film viewing mirrored this pattern.

CONCLUSIONS

Peritraumatic neural processing in multiple salience network regions and cumulative lifetime adversity interactively predicted PTSD-like symptomatology, representing a diathesis × stress framework that might guide identification of at-risk individuals and potential targets for symptom prevention after traumatic incidents.

Aetiology and treatment of nightmare disorder: State of the art and future perspectives

This consensus paper provides an overview of the state of the art in research on the aetiology and treatment of nightmare disorder and outlines further perspectives on these issues. It presents a definition of nightmares and nightmare disorder followed by epidemiological findings, and then explains existing models of nightmare aetiology in traumatized and non‐traumatized individuals. Chronic nightmares develop through the interaction of elevated hyperarousal and impaired fear extinction. This interplay is assumed to be facilitated by trait affect distress elicited by traumatic experiences, early childhood adversity and trait susceptibility, as well as by elevated thought suppression and potentially sleep‐disordered breathing. Accordingly, different treatment options for nightmares focus on their meaning, on the chronic repetition of the nightmare or on maladaptive beliefs. Clinically, knowledge of healthcare providers about nightmare disorder and the delivery of evidence‐based interventions in the healthcare system is discussed. Based on these findings, we highlight some future perspectives and potential further developments of nightmare treatments and research into nightmare aetiology.

Measuring the conditioned response: A comparison of pupillometry, skin conductance, and startle electromyography

In human fear conditioning studies, different physiological readouts can be used to track conditioned responding during fear learning. Commonly employed readouts such as skin conductance responses (SCR) or startle responses have in recent years been complemented by pupillary readouts, but to date it is unknown how pupillary readouts relate to other measures of the conditioned response. To examine differences and communalities among pupil responses, SCR, and startle responses, we simultaneously recorded pupil diameter, skin conductance, and startle electromyography in 47 healthy subjects during fear acquisition, extinction, and a recall test on 2 consecutive days. The different measures correlated only weakly, displaying most prominent differences in their response patterns during fear acquisition. Whereas SCR and startle responses habituated, pupillary measures did not. Instead, they increased in response to fear conditioned stimuli and most closely followed ratings of unconditioned stimulus (US) expectancy. Moreover, we observed that startle-induced pupil responses showed stimulus discrimination during fear acquisition, suggesting a fear potentiation of the auditory pupil reflex. We conclude that different physiological outcome measures of the conditioned response inform about different cognitive-affective processes during fear learning, with pupil responses being least affected by physiological habituation and most closely following US expectancy.

Multi-echo EPI of human fear conditioning reveals improved BOLD detection in ventromedial prefrontal cortex

Standard T₂^* weighted functional magnetic resonance imaging (fMRI) performed with echo-planar imaging (EPI) suffers from signal loss in the ventromedial prefrontal cortex (vmPFC) due to macroscopic field inhomogeneity. However, this region is of special interest to affective neuroscience and psychiatry. The Multi-echo EPI (MEPI) approach has several advantages over EPI but its performance against EPI in the vmPFC has not yet been examined in a study with sufficient statistical power using a task specifically eliciting activity in this region. We used a fear conditioning task with MEPI to compare the performance of MEPI and EPI in vmPFC and control regions in 32 healthy young subjects. We analyzed activity associated with short (12ms), standard (29ms) and long (46ms) echo times, and a voxel-wise combination of these three echo times. Behavioral data revealed successful differentiation of the conditioned versus safety stimulus; activity in the vmPFC was shown by the contrast "safety stimulus > conditioned stimulus" as in previous research and proved significantly stronger with the combined MEPI than standard single-echo EPI. Then, we aimed to demonstrate that the additional cluster extent (ventral extension) detected in the vmPFC with MEPI reflects activation in a relevant cluster (i.e., not just non-neuronal noise). To do this, we used resting state data from the same subjects to show that the time-course of this region was both connected to bilateral amygdala and the default mode network. Overall, we demonstrate that MEPI (by means of the weighted sum combination approach) outperforms standard EPI in vmPFC; MEPI performs always at least as good as the best echo time for a given brain region but provides all necessary echo times for an optimal BOLD sensitivity for the whole brain. This is relevant for affective neuroscience and psychiatry given the critical role of the vmPFC in emotion regulation.

Neural correlates of pupil dilation during human fear learning

BACKGROUND

Fear conditioning and extinction are prevailing experimental and etiological models for normal and pathological anxiety. Pupil dilations in response to conditioned stimuli are increasingly used as a robust psychophysiological readout of fear learning, but their neural correlates remain unknown. We aimed at identifying the neural correlates of pupil responses to threat and safety cues during a fear learning task.

METHODS

Thirty-four healthy subjects underwent a fear conditioning and extinction paradigm with simultaneous functional magnetic resonance imaging (fMRI) and pupillometry. After a stringent preprocessing and artifact rejection procedure, trial-wise pupil responses to threat and safety cues were entered as parametric modulations to the fMRI general linear models.

RESULTS

Trial-wise magnitude of pupil responses to both conditioned and safety stimuli correlated positively with activity in dorsal anterior cingulate cortex (dACC), thalamus, supramarginal gyrus and insula for the entire fear learning task, and with activity in the dACC during the fear conditioning phase in particular. Phasic pupil responses did not show habituation, but were negatively correlated with tonic baseline pupil diameter, which decreased during the task. Correcting phasic pupil responses for the tonic baseline pupil diameter revealed thalamic activity, which was also observed in an analysis employing a linear (declining) time modulation.

CONCLUSION

Pupil dilations during fear conditioning and extinction provide useful readouts to track fear learning on a trial-by-trial level, particularly with simultaneous fMRI. Whereas phasic pupil responses reflect activity in brain regions involved in fear learning and threat appraisal, most prominently in dACC, tonic changes in pupil diameter may reflect changes in general arousal.

Validation of non-REM sleep stage decoding from resting state fMRI using linear support vector machines

A growing body of literature suggests that changes in consciousness are reflected in specific connectivity patterns of the brain as obtained from resting state fMRI (rs-fMRI). As simultaneous electroencephalography (EEG) is often unavailable, decoding of potentially confounding sleep patterns from rs-fMRI itself might be useful and improve data interpretation. Linear support vector machine classifiers were trained on combined rs-fMRI/EEG recordings from 25 subjects to separate wakefulness (S0) from non-rapid eye movement (NREM) sleep stages 1 (S1), 2 (S2), slow wave sleep (SW) and all three sleep stages combined (SX). Classifier performance was quantified by a leave-one-subject-out cross-validation (LOSO-CV) and on an independent validation dataset comprising 19 subjects. Results demonstrated excellent performance with areas under the receiver operating characteristics curve (AUCs) close to 1.0 for the discrimination of sleep from wakefulness (S0|SX), S0|S1, S0|S2 and S0|SW, and good to excellent performance for the classification between sleep stages (S1|S2:~0.9; S1|SW:~1.0; S2|SW:~0.8). Application windows of fMRI data from about 70 s were found as minimum to provide reliable classifications. Discrimination patterns pointed to subcortical-cortical connectivity and within-occipital lobe reorganization of connectivity as strongest carriers of discriminative information. In conclusion, we report that functional connectivity analysis allows valid classification of NREM sleep stages.

Imagery rehearsal therapy in addition to treatment as usual for patients with diverse psychiatric diagnoses suffering from nightmares: a randomized controlled trial

OBJECTIVE

Nightmares are associated with psychopathology and daily distress. They are highly prevalent in a psychiatric population (30%). Currently, imagery rehearsal therapy (IRT) is the treatment of choice for nightmares. With IRT, the script of the nightmare is changed into a new dream, which is imagined during the day. However, the effects of IRT in a psychiatric population remain unknown. The aim of this study was to determine the effectiveness of IRT in a heterogeneous psychiatric population.

METHOD

Between January 2006 and July 2010, 90 patients with psychiatric disorders (DSM-IV-TR) were randomized to IRT or treatment-as-usual conditions. IRT consisted of 6 individual sessions added to the treatment as usual. Nightmare frequency was assessed using daily nightmare logs and the Nightmare Frequency Questionnaire. Nightmare distress was assessed using the Nightmare Distress Questionnaire and the Nightmare Effects Survey. General psychiatric symptoms were assessed using the Symptom Checklist-90 and a PTSD symptom questionnaire. Assessments were administered at the start of the trial, after the IRT and at follow-up 3 months later.

RESULTS

IRT showed a moderate effect (Cohen d = 0.5-0.7, P < .05) on nightmare frequency, nightmare distress, and psychopathology measures compared with treatment as usual. These effects were largely sustained at the 3-month follow-up (Cohen d = 0.4-0.6, P < .10).

CONCLUSIONS

IRT is an effective treatment for nightmares among patients with comorbid psychiatric disorders and can be employed in addition to the on-going treatment.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00291031.

Neural correlates of insight in dreaming and psychosis

The idea that dreaming can serve as a model for psychosis has a long and honourable tradition, however it is notoriously speculative. Here we demonstrate that recent research on the phenomenon of lucid dreaming sheds new light on the debate. Lucid dreaming is a rare state of sleep in which the dreamer gains insight into his state of mind during dreaming. Recent electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) data for the first time allow very specific hypotheses about the dream-psychosis relationship: if dreaming is a reasonable model for psychosis, then insight into the dreaming state and insight into the psychotic state should share similar neural correlates. This indeed seems to be the case: cortical areas activated during lucid dreaming show striking overlap with brain regions that are impaired in psychotic patients who lack insight into their pathological state. This parallel allows for new therapeutic approaches and ways to test antipsychotic medication.

One night of partial sleep deprivation affects habituation of hypothalamus and skin conductance responses

Sleep disturbances are prevalent in clinical anxiety, but it remains unclear whether they are cause and/or consequence of this condition. Fear conditioning constitutes a valid laboratory model for the acquisition of normal and pathological anxiety. To explore the relationship between disturbed sleep and anxiety in more detail, the present study evaluated the effect of partial sleep deprivation (SD) on fear conditioning in healthy individuals. The neural correlates of 1) nonassociative learning and physiological processing and 2) associative learning (differential fear conditioning) were addressed. Measurements entailed simultaneous functional MRI, EEG, skin conductance response (SCR), and pulse recordings. Regarding nonassociative learning, partial SD resulted in a generalized failure to habituate during fear conditioning, as evidenced by reduced habituation of SCR and hypothalamus responses to all stimuli. Furthermore, SCR and hypothalamus activity were correlated, supporting their functional relationship. Regarding associative learning, effects of partial SD on the acquisition of conditioned fear were weaker and did not reach statistical significance. The hypothalamus plays an integral role in the regulation of sleep and autonomic arousal. Thus sleep disturbances may play a causal role in the development of normal and possibly pathological fear by increasing the susceptibility of the sympathetic nervous system to stressful experiences.

Volitional components of consciousness vary across wakefulness, dreaming and lucid dreaming

Consciousness is a multifaceted concept; its different aspects vary across species, vigilance states, or health conditions. While basal aspects of consciousness like perceptions and emotions are present in many states and species, higher-order aspects like reflective or volitional capabilities seem to be most pronounced in awake humans. Here we assess the experience of volition across different states of consciousness: 10 frequent lucid dreamers rated different aspects of volition according to the Volitional Components Questionnaire for phases of normal dreaming, lucid dreaming, and wakefulness. Overall, experienced volition was comparable for lucid dreaming and wakefulness, and rated significantly higher for both states compared to non-lucid dreaming. However, three subscales showed specific differences across states of consciousness: planning ability was most pronounced during wakefulness, intention enactment most pronounced during lucid dreaming, and self-determination most pronounced during both wakefulness and lucid dreaming. Our data confirm the multifaceted nature of consciousness: different higher-order aspects of consciousness are differentially expressed across different conscious states.

Resting state functional MRI connectivity predicts hypothalamus-pituitary-axis status in healthy males

Homeostasis of the human stress response system is critically maintained by a hierarchical system of neural and endocrine elements for which intact negative feedback is important to prevent maladaptation towards stress. Such feedback is efficiently probed by the established combined dexamethasone-suppression/corticotropin-releasing hormone stimulation (dex/CRH) test. Here we investigate which suprahypothalamic networks might modulate the response assessed by this neuroendocrine test. Combined resting state fMRI (rs-fMRI)/EEG was acquired in 20 healthy male volunteers along with dex/CRH profiles obtained on a different day outside the scanner. Seed-based network analysis and inter-seed cross correlation analysis for selected atlas-based limbic, paralimbic and medial prefrontal cortex seeds were correlated with stimulated cortisol and adrenocorticotropin hormone (ACTH) concentrations. Lower connectivity between a left hippocampus-based network and the right hippocampus significantly predicted stimulated cortisol concentration (R(2)=0.70, corrected pcluster=0.001). Six further significantly negative correlations were detected mainly in the left anterior cingulate cortex (ACC) and the medial prefrontal cortex (mPFC). The strongest positive correlation with stimulated hormone concentration was detected for the left subcallosal ACC (ACTH, R(2)=0.57, corrected pcluster=0.009). Inter-seed connectivity mainly pointed to hippocampal/amygdala interactions as correlates of the dex/CRH response. In conclusion, resting state functional connectivity patterns of limbic, particularly hippocampal, as well as cingulate and medial prefrontal areas can explain some of the variance of the dex/CRH test in healthy subjects. Functional connectivity analysis can be considered useful to study supra-hypothalamic control systems of the HPA axis.

Regional specificity of manganese accumulation and clearance in the mouse brain: implications for manganese-enhanced MRI

Manganese-enhanced MRI has recently become a valuable tool for the assessment of in vivo functional cerebral activity in animal models. As a result of the toxicity of manganese at higher dosages, fractionated application schemes have been proposed to reduce the toxic side effects by using lower concentrations per injection. Here, we present data on regional-specific manganese accumulation during a fractionated application scheme over 8 days of 30 mg/kg MnCl2 , as well as on the clearance of manganese chloride over the course of several weeks after the termination of the whole application protocol supplying an accumulative dose of 240 mg/kg MnCl2 . Our data show most rapid accumulation in the superior and inferior colliculi, amygdala, bed nucleus of the stria terminalis, cornu ammonis of the hippocampus and globus pallidus. The data suggest that no ceiling effects occur in any region using the proposed application protocol. Therefore, a comparison of basal neuronal activity differences in different animal groups based on locally specific manganese accumulation is possible using fractionated application. Half-life times of manganese clearance varied between 5 and 7 days, and were longest in the periaqueductal gray, amygdala and entorhinal cortex. As the hippocampal formation shows one of the highest T1 -weighted signal intensities after manganese application, and manganese-induced memory impairment has been suggested, we assessed hippocampus-dependent learning as well as possible manganese-induced atrophy of the hippocampal volume. No interference of manganese application on learning was detected after 4 days of Mn(2+) application or 2 weeks after the application protocol. In addition, no volumetric changes induced by manganese application were found for the hippocampus at any of the measured time points. For longitudinal measurements (i.e. repeated manganese applications), a minimum of at least 8 weeks should be considered using the proposed protocol to allow for sufficient clearance of the paramagnetic ion from cerebral tissue.

Baseline depression levels do not affect efficacy of cognitive-behavioral self-help treatment for insomnia

BACKGROUND

Cognitive-behavioral therapy can effectively treat insomnia (CBT-I). Randomized controlled trials have shown efficacy of self-help CBT-I, but unclear is whether excluding depressive patients boosted treatment effects.

METHOD

We administered unsupported self-help CBT-I to insomnia patients with low and high depression levels. Based on the validated Centre of Epidemiological Studies-Depression (CES-D) scale, the internet-recruited sample (N = 479) was divided into three groups: low depression scores (n = 198), mild depression scores (n = 182), and high depression scores (n = 99). Follow-ups were 4 and 18 weeks after completion of the treatment.

RESULTS

At 4-week follow-up, all groups had a similar amelioration on the primary sleep measures (d = 0.1-0.7; P < 0.05) and the secondary insomnia ratings (d = 1.2; P < 0.001). The only difference was that the high/mild depression groups had a steeper reduction in depression (d = 1.0-1.1; P < 0.001) and anxiety scores (d = 0.7-0.8; P < 0.001) than the low depression group (depression and anxiety: d = 0.3; P < 0.01), possibly due to floor effects in the latter group. The observed effects were sustained at the 18-week follow-up.

CONCLUSIONS

This study showed that CBT-I is effective regardless of baseline depression levels. Treating the combination of insomnia and depression is an extra challenge since it is associated with increased sleep problems. These data may help us understand the relationship between insomnia and depression and indicate that self-help CBT-I may be a promising addition to regular depression treatment.

Additional support for the existence of skin conductance responses at unconditioned stimulus omission

The existence of a skin conductance response to an expected but omitted aversive stimulus has recently been challenged. To counter this claim, we provide a review of the literature and a temporal analysis of two independent skin conductance data sets during aversive conditioning and extinction that demonstrates a consistent and reproducible skin conductance response at omission of an anticipated aversive stimulus. The validity of this so-called unconditioned stimulus (US) omission response is relevant for skin conductance modeling in the context of neuroimaging and more generally for conditioning theory.

Neural correlates of dream lucidity obtained from contrasting lucid versus non-lucid REM sleep: a combined EEG/fMRI case study

STUDY OBJECTIVES

To investigate the neural correlates of lucid dreaming.

DESIGN

Parallel EEG/fMRI recordings of night sleep.

SETTING

Sleep laboratory and fMRI facilities.

PARTICIPANTS

Four experienced lucid dreamers.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

Out of 4 participants, one subject had 2 episodes of verified lucid REM sleep of sufficient length to be analyzed by fMRI. During lucid dreaming the bilateral precuneus, cuneus, parietal lobules, and prefrontal and occipito-temporal cortices activated strongly as compared with non-lucid REM sleep.

CONCLUSIONS

In line with recent EEG data, lucid dreaming was associated with a reactivation of areas which are normally deactivated during REM sleep. This pattern of activity can explain the recovery of reflective cognitive capabilities that are the hallmark of lucid dreaming.

Frontoparietal Connectivity and Hierarchical Structure of the Brain's Functional Network during Sleep

Frontal and parietal regions are associated with some of the most complex cognitive functions, and several frontoparietal resting-state networks can be observed in wakefulness. We used functional magnetic resonance imaging data acquired in polysomnographically validated wakefulness, light sleep, and slow-wave sleep to examine the hierarchical structure of a low-frequency functional brain network, and to examine whether frontoparietal connectivity would disintegrate in sleep. Whole-brain analyses with hierarchical cluster analysis on predefined atlases were performed, as well as regression of inferior parietal lobules (IPL) seeds against all voxels in the brain, and an evaluation of the integrity of voxel time-courses in subcortical regions-of-interest. We observed that frontoparietal functional connectivity disintegrated in sleep stage 1 and was absent in deeper sleep stages. Slow-wave sleep was characterized by strong hierarchical clustering of local submodules. Frontoparietal connectivity between IPL and superior medial and right frontal gyrus was lower in sleep stages than in wakefulness. Moreover, thalamus voxels showed maintained integrity in sleep stage 1, making intrathalamic desynchronization an unlikely source of reduced thalamocortical connectivity in this sleep stage. Our data suggest a transition from a globally integrated functional brain network in wakefulness to a disintegrated network consisting of local submodules in slow-wave sleep, in which frontoparietal inter-modular nodes may play a role, possibly in combination with the thalamus.

Statistical evaluation of recurrence quantification analysis applied on single trial evoked potential studies

OBJECTIVE

We evaluated the potential of recurrence quantification analysis (RQA) to improve the analysis of trial-by-trial-variability in event-related potentials (ERPs) experiments.

METHODS

We use an acoustic oddball paradigm to compare the efficiency of RQA with a linear amplitude based analysis of single trial ERPs with regard to the power to distinguish responses to different tone types. We further probed the robustness of both analyses towards structured noise induced by parallel magnetic resonance imaging (MRI).

RESULTS

RQA provided robust discrimination of responses to different tone types, even when EEG data were contaminated by structured noise. Yet, its power to discriminate responses to different tone types was not significantly superior to a linear amplitude analysis. RQA measures were only moderately correlated with EEG amplitudes, suggesting that RQA may extract additional information from single trial responses not detected by amplitude evaluation.

CONCLUSIONS

RQA allows quantifying signal characteristics of single trial ERPs measured with and without noise induced by parallel MRI. RQA power to discriminate responses to different tone types was similar to linear amplitude based analysis.

SIGNIFICANCE

RQA has the potential to detect differences of signal features in response to a standard oddball paradigm and provide additional trial-by-trial information compared to classical amplitude based analysis.

Dreamed movement elicits activation in the sensorimotor cortex

Since the discovery of the close association between rapid eye movement (REM) sleep and dreaming, much effort has been devoted to link physiological signatures of REM sleep to the contents of associated dreams [1-4]. Due to the impossibility of experimentally controlling spontaneous dream activity, however, a direct demonstration of dream contents by neuroimaging methods is lacking. By combining brain imaging with polysomnography and exploiting the state of "lucid dreaming," we show here that a predefined motor task performed during dreaming elicits neuronal activation in the sensorimotor cortex. In lucid dreams, the subject is aware of the dreaming state and capable of performing predefined actions while all standard polysomnographic criteria of REM sleep are fulfilled [5, 6]. Using eye signals as temporal markers, neural activity measured by functional magnetic resonance imaging (fMRI) and near-infrared spectroscopy (NIRS) was related to dreamed hand movements during lucid REM sleep. Though preliminary, we provide first evidence that specific contents of REM-associated dreaming can be visualized by neuroimaging.

Internet-delivered or mailed self-help treatment for insomnia?: a randomized waiting-list controlled trial

Cognitive Behavioral Therapy (CBT) is effective in reducing insomnia complaints, but the effects of self-help CBT have been inconsistent. The aim of this study was to determine the effectiveness of self-help for insomnia delivered in either electronic or paper-and-pencil format compared to a waiting-list. Participants kept a diary and filled out questionnaires before they were randomized into electronic (n = 216), paper-and-pencil (n = 205), or waiting-list (n = 202) groups. The intervention consisted of 6 weeks of unsupported self-help CBT, and post-tests were 4, 18, and 48 weeks after intervention. At 4-week follow-up, electronic and paper-and-pencil conditions were superior (p < .01) compared to the waiting-list condition on most daily sleep measures (Δd = 0.29-0.64), global insomnia symptoms (Δd = 0.90-1.00), depression (Δd = 0.36-0.41), and anxiety symptoms (Δd = 0.33-0.40). The electronic and paper-and-pencil groups demonstrated equal effectiveness 4 weeks after treatment (Δd = 0.00-0.22; p > .05). Effects were sustained at 48-week follow-up. This large-scale unsupported self-help study shows moderate to large effects on sleep measures that were still present after 48 weeks. Unsupported self-help CBT for insomnia therefore appears to be a promising first option in a stepped care approach.

Large-scale functional brain networks in human non-rapid eye movement sleep: insights from combined electroencephalographic/functional magnetic resonance imaging studies

This paper reviews the existing body of knowledge on the neural correlates of spontaneous oscillations, functional connectivity and brain plasticity in human non-rapid eye movement (NREM) sleep. The first section reviews the evidence that specific sleep events as slow waves and spindles are associated with transient increases in regional brain activity. The second section describes the changes in functional connectivity during NREM sleep, with a particular focus on changes within a low-frequency, large-scale functional brain network. The third section will discuss the possibility that spontaneous oscillations and differential functional connectivity are related to brain plasticity and systems consolidation, with a particular focus on motor skill acquisition. Implications for the mode of information processing per sleep stage and future experimental studies are discussed.

Effects of rapid eye movement sleep deprivation on fear extinction recall and prediction error signaling

In a temporal difference learning approach of classical conditioning, a theoretical error signal shifts from outcome deliverance to the onset of the conditioned stimulus. Omission of an expected outcome results in a negative prediction error signal, which is the initial step towards successful extinction and may therefore be relevant for fear extinction recall. As studies in rodents have observed a bidirectional relationship between fear extinction and rapid eye movement (REM) sleep, we aimed to test the hypothesis that REM sleep deprivation impairs recall of fear extinction through prediction error signaling in humans. In a three-day design with polysomnographically controlled REM sleep deprivation, 18 young, healthy subjects performed a fear conditioning, extinction and recall of extinction task with visual stimuli, and mild electrical shocks during combined functional magnetic resonance imaging (fMRI) and skin conductance response (SCR) measurements. Compared to the control group, the REM sleep deprivation group had increased SCR scores to a previously extinguished stimulus at early recall of extinction trials, which was associated with an altered fMRI time-course in the left middle temporal gyrus. Post-hoc contrasts corrected for measures of NREM sleep variability also revealed between-group differences primarily in the temporal lobe. Our results demonstrate altered prediction error signaling during recall of fear extinction after REM sleep deprivation, which may further our understanding of anxiety disorders in which disturbed sleep and impaired fear extinction learning coincide. Moreover, our findings are indicative of REM sleep related plasticity in regions that also show an increase in activity during REM sleep.

Development of the brain's default mode network from wakefulness to slow wave sleep

Falling asleep is paralleled by a loss of conscious awareness and reduced capacity to process external stimuli. Little is known on sleep-associated changes of spontaneously synchronized anatomical networks as detected by resting-state functional magnetic resonance imaging (rs-fMRI). We employed functional connectivity analysis of rs-fMRI series obtained from 25 healthy participants, covering all non-rapid eye movement (NREM) sleep stages. We focused on the default mode network (DMN) and its anticorrelated network (ACN) that are involved in internal and external awareness during wakefulness. Using independent component analysis, cross-correlation analysis (CCA), and intraindividual dynamic network tracking, we found significant changes in DMN/ACN integrity throughout the NREM sleep. With increasing sleep depth, contributions of the posterior cingulate cortex (PCC)/retrosplenial cortex (RspC), parahippocampal gyrus, and medial prefrontal cortex to the DMN decreased. CCA revealed a breakdown of corticocortical functional connectivity, particularly between the posterior and anterior midline node of the DMN and the DMN and the ACN. Dynamic tracking of the DMN from wakefulness into slow wave sleep in a single subject added insights into intraindividual network fluctuations. Results resonate with a role of the PCC/RspC for the regulation of consciousness. We further submit that preserved corticocortical synchronization could represent a prerequisite for maintaining internal and external awareness.

Cognitive-behavioral self-help treatment for nightmares: a randomized controlled trial

BACKGROUND

Several cognitive-behavioral techniques are effective in reducing nightmare frequency, but the therapeutic factor (e.g. cognitive restructuring, systematic desensitization) remains unclear. The aim of this study was to compare the nightmare treatments imagery rehearsal therapy (IRT), exposure, and recording (keeping a diary)--in a self-help format--with a waiting list.

METHODS

Participants were recruited through a Dutch nightmare website. After completion of the baseline questionnaires, 399 participants were randomly assigned to a condition, received a 6-week self-help treatment (or were placed on the waiting list), and filled out the post-treatment measurements 11 weeks after baseline.

RESULTS

Compared to the waiting list, IRT and exposure were effective in ameliorating nightmare frequency and distress, subjective sleep quality, anxiety (after imagery rehearsal), and depression (after exposure; Δd = 0.25-0.56). Compared to recording, IRT reduced nightmare frequency while exposure reduced nightmare distress (Δd = 0.20-0.30; p < 0.05). The recording condition was more effective compared to the waiting list in ameliorating nightmare frequency, nightmare distress, and subjective sleep quality (Δd = 0.19-0.28; p < 0.05). IRT had a more rapid reduction on the diary compared to exposure and recording.

CONCLUSIONS

IRT and exposure appear equally effective in ameliorating nightmare complaints. Exposure to nightmare imagery may function as the crucial therapeutic factor; however, cognitive restructuring may be a useful addition to increase immediate effects.

Modelling hierarchical structure in functional brain networks

In this work, we focus on a complex-network approach for the study of the brain. In particular, we consider functional brain networks, where the vertices represent different anatomical regions and the links their functional connectivity. First, we build these networks using data obtained with functional magnetic resonance imaging. Then, we analyse the main characteristics of these complex networks, including degree distribution, the presence of modules and hierarchical structure. Finally, we present a network model with dynamical nodes and adaptive links. We show that the model allows for the emergence of complex networks with characteristics similar to those observed in functional brain networks.

A systematic review of cognitive-behavioral treatment for nightmares: toward a well-established treatment

The aim of this review is to evaluate the effectiveness of cognitive behavioral therapy (CBT) on nightmare frequency and to determine which kind of CBT is the most effective treatment. A systematic literature search was carried out in PsychInfo and PubMed articles published on or before May 1, 2008. The inclusion criteria were: nightmare treatment study, use of nonpharmacological treatment, not a qualitative case study, randomized-controlled trial (RCT). After selection, 12 peer-reviewed studies about 9 RCTs remained (2 follow-up studies and one displaying preliminary results). Several interventions have been reviewed including, recording one's nightmares, relaxation, exposure, and techniques of cognitive restructuring. The 12 evaluated articles varied in quality, and none fulfilled CONSORT guidelines. All articles used nightmare frequency as the primary dependent variable, and all found significant in-group differences (pre vs. post) for intervention or placebo (range d = 0.7-2.9). Five studies were able to find a significant group effect for the intervention compared to a waiting list control group. Only one study found significant differences between 2 intervention groups. Nightmare-focused CBT (exposure and imagery rehearsal therapy [IRT]) revealed better treatment outcomes than indirect CBT (relaxation, recording). IRT and exposure showed no meaningful differences, but only one RCT directly compared both techniques. Three different research groups demonstrated the effects of exposure, but only one group showed the effect of IRT. Thus, RCTs that compare IRT with exposure by independent research groups are much needed.