The impact of melancholia versus non-melancholia on resting-state, EEG alpha asymmetry: electrophysiological evidence for depression heterogeneity

Differentiating melancholic and non-melancholic depression via biological markers: A review

OBJECTIVES

Melancholia is a severe form of depression that is typified by greater genetic and biological influence, distinct symptomatology, and preferential response to physical treatment. This paper sought to broadly overview potential biomarkers of melancholia to benefit differential diagnosis, clinical responses and treatment outcomes. Given nuances in distinguishing melancholia as its own condition from other depressive disorder, we emphasised studies directly comparing melancholic to non-melancholic depression.

METHODS

A comprehensive literature search was conducted. Key studies were identified and summarised qualitatively.

RESULTS

105 studies in total were identified. These studies covered a wide variety of biomarkers, and largely fell into three domains: endocrinological (especially cortisol levels, particularly in response to the dexamethasone suppression test), neurological, and immunological (particularly inflammatory markers). Less extensive evidence also exists for metabolic, genetic, and cardiovascular markers.

CONCLUSIONS

Definitive conclusions were predominantly limited due to substantial heterogeneity in how included studies defined melancholia. Furthermore, this heterogeneity could be responsible for the between- and within-group variability observed in the candidate biomarkers that were examined. Therefore, clarifying these definitional parameters may help identify underlying patterns in biomarker expression to improve diagnostic and therapeutic precision for the depressive disorders.

Alpha wave asymmetry is associated with only one component of melancholia, and in different directions across brain regions

Alpha wave asymmetry inconsistently correlates with Major Depressive Disorder (MDD). One possible reason for this inconsistency is the heterogeneity of MDD, leading to study of depressive 'subtypes', one of which is Melancholia. To investigate the correlation between Melancholia and alpha-wave asymmetry, 100 community participants (44 males, 56 females; aged at least 18 yr) completed the Zung self-rated Depression Scale, and underwent 3 min of eyes closed EEG recording from 24 scalp sites. There was no significant correlation between EEG data and Melancholia total score for the entire sample, but there was for those participants who had clinically significant depression (n = 33). When examined at the level of individual Melancholia scale items, significant EEG data correlations were found for some of the items but not for others. Factor analysis revealed a two-factor structure for the Melancholia scale, only one of which exhibited significant correlations with EEG AA data. Further exploration of those data identified two subcomponents of that Melancholia factor, one which was inversely correlated with frontal alpha asymmetry, and another which was directly correlated with parietal-occipital alpha wave asymmetry. These findings suggest that Melancholia may itself be heterogeneous, similarly to MDD, and rely upon different aspects of cognitive function.

Network analysis of frontal lobe alpha asymmetry confirms the neurophysiological basis of four subtypes of depressive behavior

Introduction

Although depression is widespread carries a major disease burden, current treatments remain non-universally effective, arguably due to the heterogeneity of depression, and leading to the consideration of depressive "subtypes" or "depressive behavior subtypes." One such model of depressive behavior (DB) subtypes was investigated for its associations with frontal lobe asymmetry (FLA), using a different data analytic procedure than in previous research in this field.

Methods

100 community volunteers (54 males, 46 females) aged between 18 yr. and 75 years (M = 32.53 yr., SD = 14.13 yr) completed the Zung Self-rating Depression Scale (SDS) and underwent 15 min of eyes closed EEG resting data collection across 10 frontal lobe sites. DB subtypes were defined on the basis of previous research using the SDS, and alpha-wave (8-13 Hz) data produced an index of FLA. Data were examined via network analysis.

Results

Several network analyses were conducted, producing two models of the association between DB subtypes and FLA, confirming unique neurophysiological profiles for each of the four DB subtypes.

Discussion

As well as providing a firm basis for using these DB subtypes in clinical settings, these findings provide a reasonable explanation for the inconsistency in previous FLA-depression research.

EEG frontal lobe asymmetry as a function of sex, depression severity, and depression subtype

To investigate possible contributors to the inconsistent association between frontal lobe asymmetry (FLA) and depression, EEG data were collected across five frontal sites, and examined for their associations with four subtypes of depression (Depressed mood, Anhedonia, Cognitive depression, Somatic depression). One hundred community volunteers (54 males, 46 females) aged at least 18 yr completed standardized scales for depression and anxiety, and gave EEG data under Eyes Open and Eyes Closed conditions. Results indicated that, although there was no significant correlation between the differences in EEG power across each of the five pairs of frontal sites and total depression scores, there were several meaningful correlations (accounting for at least 10% of the variance) between specific EEG site differences data and each of the four depression subtypes. There were also different patterns of association between FLA and the depression subtypes according to sex, and total depression severity. These findings help to explain the apparent inconsistency in previous FLA-depression results, and argue for a more nuanced approach to this hypothesis.

Functional role of frontal electroencephalogram alpha asymmetry in the resting state in patients with depression: A review

Depression is a psychological disorder that affects the general public worldwide. It is particularly important to make an objective and accurate diagnosis of depression, and the measurement methods of brain activity have gradually received increasing attention. Resting electroencephalogram (EEG) alpha asymmetry in patients with depression shows changes in activation of the alpha frequency band of the left and right frontal cortices. In this paper, we review the findings of the relationship between frontal EEG alpha asymmetry in the resting state and depression. Based on worldwide studies, we found the following: (1) Compared with individuals without depression, those with depression showed greater right frontal EEG alpha asymmetry in the resting state. However, the pattern of frontal EEG alpha asymmetry in the resting state in depressive individuals seemed to disappear with age; (2) Compared with individuals without maternal depression, those with maternal depression showed greater right frontal EEG alpha asymmetry in the resting state, which indicated that genetic or experience-based influences have an impact on frontal EEG alpha asymmetry at rest; and (3) Frontal EEG alpha asymmetry in the resting state was stable, and little or no change occurred after antidepressant treatment. Finally, we concluded that the contrasting results may be due to differences in methodology, clinical characteristics, and participant characteristics.

The Role of Alpha Oscillations among the Main Neuropsychiatric Disorders in the Adult and Developing Human Brain: Evidence from the Last 10 Years of Research

Alpha oscillations (7-13 Hz) are the dominant rhythm in both the resting and active brain. Accordingly, translational research has provided evidence for the involvement of aberrant alpha activity in the onset of symptomatological features underlying syndromes such as autism, schizophrenia, major depression, and Attention Deficit and Hyperactivity Disorder (ADHD). However, findings on the matter are difficult to reconcile due to the variety of paradigms, analyses, and clinical phenotypes at play, not to mention recent technical and methodological advances in this domain. Herein, we seek to address this issue by reviewing the literature gathered on this topic over the last ten years. For each neuropsychiatric disorder, a dedicated section will be provided, containing a concise account of the current models proposing characteristic alterations of alpha rhythms as a core mechanism to trigger the associated symptomatology, as well as a summary of the most relevant studies and scientific contributions issued throughout the last decade. We conclude with some advice and recommendations that might improve future inquiries within this field.

The novel frontal alpha asymmetry factor and its association with depression, anxiety, and personality traits

Frontal alpha asymmetry (FAA) is widely examined in EEG research, yet a procedural consensus on its assessment is lacking. In this study, we tested a latent factorial approach to measure FAA. We assessed resting-state FAA at broad, low, and high alpha bands (8-13; 8-10.5; and 11-13 Hz) using mastoids as reference electrodes and Current Source Density (CSD) transformation (N = 139 non-clinical participants). From mastoid-referenced data, we extracted a frontal alpha asymmetry factor (FAAf) and a parietal factor (PAAf) subjecting all asymmetry indices to a varimax-rotated, principal component analysis. We explored split-half reliability and discriminant validity of the mastoid factors and the mastoid and CSD raw asymmetry indices (F3/4, F7/8, P3/4, and P7/8). Both factor and raw scores reached an excellent split-half reliability (>.99), but only the FAAf reached the maximum discriminant validity from parietal scores. Next, we explored the correlations of latent factor and raw FAA scores with symptoms of depression, anxiety, and personality traits to determine which associations were driven by FAA after variance from parietal activity was removed. After correcting for false discovery rate, only FAAf at the low alpha band was negatively associated with depression symptoms (a latent CES-D factor) and significantly diverged from PAAf's association with depression symptoms. With respect to personality traits, only CSD-transformed F7/8 was positively correlated with Conscientiousness and significantly diverged from the correlations between Conscientiousness and P3/4 and P7/8. Overall, the latent factor approach shows promise for isolating functionally distinct resting-state EEG signatures, although further research is needed to examine construct validity.

Electroencephalography Correlates of Well-Being Using a Low-Cost Wearable System

Electroencephalography (EEG) alpha asymmetry is thought to reflect crucial brain processes underlying executive control, motivation, and affect. It has been widely used in psychopathology and, more recently, in novel neuromodulation studies. However, inconsistencies remain in the field due to the lack of consensus in methodological approaches employed and the recurrent use of small samples. Wearable technologies ease the collection of large and diversified EEG datasets that better reflect the general population, allow longitudinal monitoring of individuals, and facilitate real-world experience sampling. We tested the feasibility of using a low-cost wearable headset to collect a relatively large EEG database (N = 230, 22-80 years old, 64.3% female), and an open-source automatic method to preprocess it. We then examined associations between well-being levels and the alpha center of gravity (CoG) as well as trait EEG asymmetries, in the frontal and temporoparietal (TP) areas. Robust linear regression models did not reveal an association between well-being and alpha (8-13 Hz) asymmetry in the frontal regions, nor with the CoG. However, well-being was associated with alpha asymmetry in the TP areas (i.e., corresponding to relatively less left than right TP cortical activity as well-being levels increased). This effect was driven by oscillatory activity in lower alpha frequencies (8-10.5 Hz), reinforcing the importance of dissociating sub-components of the alpha band when investigating alpha asymmetries. Age was correlated with both well-being and alpha asymmetry scores, but gender was not. Finally, EEG asymmetries in the other frequency bands were not associated with well-being, supporting the specific role of alpha asymmetries with the brain mechanisms underlying well-being levels. Interpretations, limitations, and recommendations for future studies are discussed. This paper presents novel methodological, experimental, and theoretical findings that help advance human neurophysiological monitoring techniques using wearable neurotechnologies and increase the feasibility of their implementation into real-world applications.

Orbitofrontal and Cingulate Thickness Asymmetry Associated with Depressive Symptom Dimensions

Both clinical depression and subthreshold depressive symptoms have been associated with alterations in cortical thickness. Studies have yielded conflicting results regarding whether cortical thinning or cortical thickening best characterize the depressive state. Also unclear is whether cortical thickness differences are lateralized. This study examined the relationship between depressive symptom dimensions and cortical thickness asymmetry in cingulate and orbitofrontal regions. Fifty-four community-dwelling adults between the ages of 18 and 81 years received a 3-Tesla magnetic resonance imaging scan and completed the Center for Epidemiologic Studies Depression Scale (CES-D). Cortical thickness values were extracted for the rostral anterior cingulate, caudal anterior cingulate, posterior cingulate, isthmus cingulate, and orbitofrontal cortex. An asymmetry index was calculated for each region. Data were analyzed using separate general linear models for each region, in which the CES-D somatic symptoms, negative affect, and anhedonia subscale scores predicted the asymmetry indices, controlling for age and sex. Higher scores on the anhedonia subscale were associated with right-sided asymmetry in orbitofrontal thickness, whereas higher somatic symptom subscale scores predicted greater left-sided asymmetry in posterior cingulate thickness. Follow-up analyses showed the orbitofrontal effect was specific to the medial, not the lateral, orbitofrontal cortex. These results suggest asymmetries in cortical thickness are apparent at even subthreshold levels of depressive symptoms, as all but five participants were below the CES-D cutoff for clinical depression, and that the relationship varies for different symptom dimensions of depression. Understanding brain asymmetries across the range of depressive symptom severity is important for informing targeted depression treatment.

Electroencephalogram patterns in patients comorbid with major depressive disorder and anxiety symptoms: Proposing a hypothesis based on hypercortical arousal and not frontal or parietal alpha asymmetry

BACKGROUND

Major depressive disorder (MDD) is often comorbid with anxiety disorders or symptoms. Brain hyperactivity, frontal alpha asymmetry (FAA), and parietal alpha asymmetry (PAA) have been considered as trait markers in patients with MDD. This study investigated the electroencephalogram (EEG) patterns among patients with MDD comorbid with anxiety symptoms.

METHODS

One hundred and thirty-five patients with MDD comorbid with anxiety (MDD group) and 135 healthy controls (HC group) were analyzed. The Beck Depression Inventory-II (BDI-II) and Beck Anxiety Inventory (BAI) were completed, and 19 EEG channels were measured during the resting state, depressive recall and recovery tasks, and happiness recall and recovery tasks. FAA and PAA were computed by log (F4 alpha)-log (F3 alpha) and log (P4 alpha)-log (P3 alpha).

RESULTS

The FAA and PAA indices between the two groups showed no significant differences; however, compared with the HC group, the MDD group had lower total delta and theta values, and higher total beta, low beta, and high beta values in the resting state. The total beta value positively correlated with the BDI-II and BAI scores in the MDD group.

LIMITATIONS

Most patients had anxious MDD and taking prescriptions, antidepressants or benzodiazepine may affect EEG patterns.

CONCLUSION

Compared with HCs, patients with MDD comorbid with anxiety had a higher beta activity in the entire brain region, supporting the role of brain hyperactivity, instead of FAA or PAA, as a trait marker in these patients. A neurofeedback protocol could be developed in future based on the brain hyperactivity findings.

Electroencephalographic Parameters Differentiating Melancholic Depression, Non-melancholic Depression, and Healthy Controls. A Systematic Review

Introduction: The objective of this systematic review was to investigate whether electroencephalographic parameters can serve as a tool to distinguish between melancholic depression, non-melancholic depression, and healthy controls in adults. Methods: A systematic review comprising an extensive literature search conducted in PubMed, Embase, Google Scholar, and PsycINFO in August 2020 with monthly updates until November 1st, 2020. In addition, we performed a citation search and scanned reference lists. Clinical trials that performed an EEG-based examination on an adult patient group diagnosed with melancholic unipolar depression and compared with a control group of non-melancholic unipolar depression and/or healthy controls were eligible. Risk of bias was assessed by the Strengthening of Reporting of Observational Studies in Epidemiology (STROBE) checklist. Results: A total of 24 studies, all case-control design, met the inclusion criteria and could be divided into three subgroups: Resting state studies (n = 5), sleep EEG studies (n = 10), and event-related potentials (ERP) studies (n = 9). Within each subgroup, studies were characterized by marked variability on almost all levels, preventing pooling of data, and many studies were subject to weighty methodological problems. However, the main part of the studies identified one or several EEG parameters that differentiated the groups. Conclusions: Multiple EEG modalities showed an ability to distinguish melancholic patients from non-melancholic patients and/or healthy controls. The considerable heterogeneity across studies and the frequent methodological difficulties at the individual study level were the main limitations to this work. Also, the underlying premise of shifting diagnostic paradigms may have resulted in an inhomogeneous patient population. Systematic Review Registration: Registered in the PROSPERO registry on August 8th, 2020, registration number CRD42020197472.

Frontal alpha asymmetry and emotional processing in youth with psychopathic traits

Emotional processing deficits are often considered central to psychopathy. There is evidence that those high in psychopathy pay less attention to emotional stimuli, and it is possible that these individuals experience diminished withdrawal motivation or heightened approach motivation in response to emotional stimuli. Studying emotional processing abnormalities, especially among youth, may be essential for better understanding psychopathy's development and for informing interventions. However, few studies on psychopathy have experimentally manipulated emotional processing, and despite the growing literature on neuroscience and psychopathy, there are aspects of neural activity that have yet to be investigated. The current study used a sample of 52 justice-involved youth to examine how psychopathy, as measured by the Proposed Specifiers for Conduct Disorder scale, relates to frontal alpha asymmetry (FAA), a neural correlate of approach and withdrawal motivation. Alpha asymmetry was first measured at rest and then while youth were asked to process emotional stimuli spontaneously as well as to increase and decrease their responses to emotional stimuli. Results indicated that total psychopathy was not related to FAA at rest or during task performance. However, youth higher in callous-unemotional traits demonstrated similar patterns of neural activity to youth lower in callous-unemotional traits when instructed to increase their response to emotional stimuli. These findings were not evident for grandiose-manipulative or daring-impulsive traits. These findings may indicate that youth high in callous-unemotional traits are capable of modulating their emotional responding, which could in turn have treatment implications for youth high in psychopathic traits.

Multilayer MEG functional connectivity as a potential marker for suicidal thoughts in major depressive disorder

Major depressive disorder (MDD) is highly heterogeneous in its clinical presentation. The present exploratory study used magnetoencephalography (MEG) to investigate electrophysiological intrinsic connectivity differences between healthy volunteers and unmedicated participants with treatment-resistant MDD. The study examined canonical frequency bands from delta through gamma. In addition to group comparisons, correlational studies were conducted to determine whether connectivity was related to five symptom factors: depressed mood, tension, negative cognition, suicidal thoughts, and amotivation. The MDD and healthy volunteer groups did not differ significantly at baseline when corrected across all frequencies and clusters, although evidence of generalized slowing in MDD was observed. Notably, however, electrophysiological connectivity was strongly related to suicidal thoughts, particularly as coupling of low frequency power fluctuations (delta and theta) with alpha and beta power. This analysis revealed hub areas underlying this symptom cluster, including left hippocampus, left anterior insula, and bilateral dorsolateral prefrontal cortex. No other symptom cluster demonstrated a relationship with neurophysiological connectivity, suggesting a specificity to these results as markers of suicidal ideation.

Women with Major Depressive Disorder, Irrespective of Comorbid Anxiety Disorders, Show Blunted Bilateral Frontal Responses during Win and Loss Anticipation

BACKGROUND

Electroencephalography (EEG) studies suggest that major depressive disorder (MDD) is associated with lower left than right frontal brain activity (asymmetry), a pattern appearing stronger in women than men, and when elicited during emotionally-relevant paradigms versus an uncontrolled resting state. However, it is unclear whether this asymmetry pattern generalizes to the common presentation of MDD with co-occurring anxiety. Moreover, asymmetry may differ for anxiety subtypes, wherein anxious apprehension (AnxApp: worry characteristic of generalized anxiety disorder) appears left-lateralized, but anxious arousal (AnxAro: panic characteristic of social anxiety, posttraumatic stress, and panic disorders) may be right-lateralized.

METHODS

This analysis attempted to replicate frontal EEG asymmetry patterns using functional magnetic resonance imaging (fMRI). Participants completed clinical interviews and a monetary incentive delay (MID) task during fMRI recording. We compared five groups of right-handed women from the Tulsa 1000 study, MDD (n=40), MDD-AnxApp (n=26), MDD-AnxAro (n=34), MDD-Both (with AnxApp and AnxAro; n=26), and healthy controls (CTL; n=24), as a function of MID anticipation condition (no win/loss, win, loss) and hemisphere on frontal blood oxygen-level-dependent (BOLD) signal.

RESULTS

CTL exhibited higher bilateral superior, middle, and inferior middle frontal gyrus BOLD signal than the four MDD groups for high arousal (win and loss) conditions. However, frontal attenuations were unrelated to current depression/anxiety symptoms, suggestive of a trait as opposed to a state marker.

LIMITATIONS

This was a cross-sectional analysis restricted to women.

CONCLUSIONS

Reduced prefrontal cortex recruitment during processing of both positively and negatively valenced stimuli is consistent with the emotion context insensitivity theory of MDD.

Brainwaves Oscillations as a Potential Biomarker for Major Depression Disorder Risk

Major depressive disorder (MDD) is a multidimensional disorder that is characterized by the presence of alterations in mood, cognitive capacity, sensorimotor, and homeostatic functions. Given that about half of the patients diagnosed with MDD do not respond to the various current treatments, new techniques are being sought to predict not only the course of the disease but also the characteristics that differentiate responders from non-responders. Using the electroencephalogram, a noninvasive and inexpensive tool, most studies have proposed that patients with MDD have some lateralization in brain electrical activity, with alterations in alpha and theta rhythms being observed, which would be related to dysfunctions in emotional capacity such as the absence or presence of responses to the different existing treatments. These alterations help in the identification of subjects at high risk of suffering from depression, in the differentiation into responders and nonresponders to various therapies (pharmacological, electroconvulsive therapy, and so on), as well as to establish in which period of the disease the treatment will be more effective. Although the data are still inconclusive and more research is needed, these alpha and theta neurophysiological markers could support future clinical practice when it comes to establishing an early diagnosis and treating state disorders more successfully and accurately of mood disorders.

The effects of alpha asymmetry and high-beta down-training neurofeedback for patients with the major depressive disorder and anxiety symptoms

BACKGROUND

Alpha-asymmetry neurofeedback (ALAY) was applied to patients with major depressive disorder (MDD) based on the theory of frontal alpha asymmetry. Neurophysiological studies have found a higher high-beta activity of electroencephalography (EEG) at the posterior cortex among patients with comorbid MDD and anxiety symptoms. The present study examined the effects of ALAY and high-beta down-training (Beta) neurofeedback in symptoms of depression and anxiety and EEG parameters.

METHOD

Eighty-seven patients with comorbid MDD and anxiety symptoms were allocated to the ALAY, Beta, or control groups. Both neurofeedback groups received ten-session neurofeedback. All participants completed the Beck Depression Inventory II (BDI-II), Beck Anxiety Inventory (BAI), and five minutes resting EEG recording at pre-test and post-test. EEG raw signals were transformed into an A1 score [log (F4 alpha) - log (F3 alpha)], P3 and P4 high-beta power.

RESULTS

BDI-II and BAI scores decreased at post-test in both ALAY and Beta groups, but no significant difference between the two groups. No significant interaction effect in A1 score at pre-test and post-test between the ALAY, Beta, and control groups. The P3 high-beta was significantly decreased in the Beta group, an increase in the control group, and no change in the ALAY group at post-test compared to the pre-test.

CONCLUSIONS

Both neurofeedback groups decreased symptoms of depression and anxiety. The Beta group was more effective in decreasing high-beta power at the parietal cortex compared to other groups. This non-invasive psychological intervention can be used in the future for patients with comorbid MDD and anxiety symptoms.

Childhood trauma and dissociative symptoms predict frontal EEG asymmetry in borderline personality disorder

Frontal EEG asymmetry (FEA) has been studied as both state and trait parameter in emotion regulation and affective disorders. Its significance in borderline personality disorder (BPD) remains largely unknown. Twenty-six BPD patients and 26 healthy controls underwent EEG before and after mood induction using aversive images. A slight but significant shift from left- to right-sided asymmetry over prefrontal electrodes occurred across all subjects. In BPD baseline FEA over F7 and F8 correlated significantly with childhood trauma and functional neurological "conversion" symptoms as assessed by respective questionnaires. Regression analysis revealed a predictive role of both childhood trauma and dissociative neurological symptoms. FEA offers a relatively stable electrophysiological correlate of BPD psychopathology that responds only minimally to acute mood changes. Future studies should address whether this psychophysiological association is universal for trauma- and dissociation-related disorders, and whether it is responsive to psychotherapy.

Electroencephalogram alpha asymmetry in patients with depressive disorders: current perspectives

PURPOSE

Electroencephalogram (EEG) alpha asymmetry (AA) in depressive disorders has been of interest over the last few decades, but it continues to remain unclear whether EEG AA can discriminate between healthy and depressive individuals.

MATERIALS AND METHODS

A systematic literature search for papers addressing EEG AA using the keywords alpha asymmetry, depression, and EEG was performed in PubMed. All studies were checked for sample size, gender, handedness, reference, recording protocol, EEG band range, impedance, type of analysis, drugs, and comorbidity.

RESULTS

A total of 61 articles were found, of which 44 met our inclusion criteria. They have been consecutively analyzed in respect of methodology and results. Approximately 25% (11/44) of the studies did not mention or ignored handedness, 41% (18/44) of the studies used data with only self-reported handedness, and only 34.1% (15/44) of all studies tested handedness. Only 35% (15/44) of the studies reported pharmacological treatment, and only 35% (15/44) of the studies controlled for medication. A total of 52% (23/44) of the studies reported comorbidity, and only 30% (13/44) of the studies controlled for comorbidity. Only 29.6% (13/44) of the studies reported education. In all, 30.5% (13/44) of the studies analyzed group differences and correlations, while 15.9 (7/44) of the studies used only correlational analyses. A total of 52.3% (23/44) of the studies analyzed only group differences. Alpha range was fixed (8-13 Hz) in 59.1% (26/44) of all studies. Reference to common average was used in seven of 44 studies (15.9%). In all, nine of 44 (20.5%) studies used the midline central position as reference, 22 of 44 (50%) studies used the ear or the mastoid as reference, and four of 44 (9.1%) studies used the nose as reference.

CONCLUSION

Discriminative power of EEG AA for depressed and healthy controls remains unclear. A systematic analysis of 44 studies revealed that differences in methodology and disregarding proper sampling are problematic. Ignoring handedness, gender, age, medication, and comorbidity could explain inconsistent findings. Hence, we formulated a guideline for requirements for future studies on EEG AA in order to allow for better comparisons.

Subtypes of depression and their overlap in a naturalistic inpatient sample of major depressive disorder

Subtyping depression is important in order to further delineate biological causes of depressive syndromes. The aim of this study was to evaluate clinical and outcome characteristics of distinct subtypes of depression and to assess proportion and features of patients fulfilling criteria for more than one subtype. Melancholic, atypical and anxious subtypes of depression were assessed in a naturalistic sample of 833 inpatients using DSM-IV specifiers based on operationalized criteria. Baseline characteristics and outcome criteria at discharge were compared between distinct subtypes and their overlap. A substantial proportion of patients (16%) were classified with more than one subtype of depression, 28% were of the distinct anxious, 7% of the distinct atypical and 5% of the distinct melancholic subtype. Distinct melancholic patients had shortest duration of episode, highest baseline depression severity, but were more often early improvers; distinct anxious patients had higher NEO-Five Factor Inventory (NEO-FFI) neuroticism scores compared with patients with unspecific subtype. Melancholic patients with overlap of anxious features had worse treatment outcome compared to distinct melancholic and distinct anxious subtype. Distinct subtypes differed in only few variables and patients with overlap of depression subtypes may have independent clinical and outcome characteristics. Studies investigating biological causes of subtypes of depression should take influence of features of other subtypes into account.

Frontal alpha asymmetry as a diagnostic marker in depression: Fact or fiction? A meta-analysis

BACKGROUND

Frontal alpha asymmetry (FAA) has frequently been reported as potential discriminator between depressed and healthy individuals, although contradicting results have been published. The aim of the current study was to provide an up to date meta-analysis on the diagnostic value of FAA in major depressive disorder (MDD) and to further investigate discrepancies in a large cross-sectional dataset.

METHODS

SCOPUS database was searched through February 2017. Studies were included if the article reported on both MDD and controls, provided an FAA measure involving EEG electrodes F3/F4, and provided data regarding potential covariates. Hedges' d was calculated from FAA means and standard deviations (SDs). Potential covariates, such as age and gender, were explored. Post hoc analysis was performed to elucidate interindividual differences that could explain interstudy discrepancies.

RESULTS

16 studies were included (MDD: n = 1883, controls: n = 2161). After resolving significant heterogeneity by excluding studies, a non-significant Grand Mean effect size (ES) was obtained (d = - 0.007;CI = [- 0.090]-[0.075]). Crosssectional analyses showed a significant three-way interaction for Gender × Age × Depression severity in the depressed group, which was prospectively replicated in an independent sample.

CONCLUSIONS

The main result was a non-significant, negligible ES, demonstrating limited diagnostic value of FAA in MDD. The high degree of heterogeneity across studies indicates covariate influence, as was confirmed by crosssectional analyses, suggesting future studies should address this Gender × Age × Depression severity interaction. Upcoming studies should focus more on prognostic and research domain usages of FAA rather than a pure diagnostic tool.

Depression symptom dimensions and asymmetrical frontal cortical activity while anticipating reward

Unipolar depression has been characterized as involving diminished approach motivation and reward sensitivity. A psychophysiological indicator of approach motivation involves an asymmetry in frontal EEG activity, such that greater left relative to right frontal cortical activity indicates increased approach motivation. Consistent with the perspective of reduced approach motivation tendencies, depression has been associated with decreased relative left frontal cortical activity. To date, supporting research has primarily relied on categorical diagnoses or composite symptom counts. However, given the heterogeneity in depression, it is unclear what specific symptom dimensions relate to decreased relative left frontal cortical activity. The present study examined the association between multiple depression symptom dimensions and asymmetrical frontal cortical activity while anticipating reward in separate undergraduate (n = 75) and clinical samples (current major depressive disorder [n = 68] and never depressed controls [n = 67]). All participants completed the Inventory of Depression and Anxiety Symptoms, a self-report measure of factor-analytically derived symptom dimensions. Frontal cortical activity was assessed during a computerized slot machine task while participants anticipated potential monetary reward or no incentive. In undergraduates with low depression symptoms and never depressed controls, reward trials relative to no-incentive trials elicited greater relative left frontal cortical activity. Furthermore, in both samples across all participants, increased dysphoria and lassitude symptoms were associated with decreased relative left frontal cortical activity while anticipating reward. The present study suggests that depression symptoms consistent with motivational disengagement are associated with decreased relative left frontal cortical activity.

Frontal EEG asymmetry in borderline personality disorder is associated with alexithymia

BACKGROUND

Frontal EEG asymmetry is a widely studied correlate of emotion processing and psychopathology. Recent research suggests that frontal EEG asymmetry during resting state is related to approach/withdrawal motivation and is also found in affective disorders such as major depressive disorder. Patients with borderline personality disorder (BPD) show aberrant behavior in relation to both approach and withdrawal motivation, which may arguably be associated with their difficulties in emotion processing. The occurrence and significance of frontal EEG asymmetry in BPD, however, has received little attention.

RESULTS

Thirty-seven BPD patients and 39 controls underwent resting EEG and completed several psychometric questionnaires. While there were no between-group differences in frontal EEG asymmetry, in BPD frontal EEG asymmetry scores correlated significantly with alexithymia. That is, higher alexithymia scores were associated with relatively lower right-frontal activity. A subsequent analysis corroborated the significant interaction between frontal EEG asymmetry and alexithymia, which was moderated by group.

CONCLUSIONS

Our findings reveal that lower right frontal EEG asymmetry is associated with alexithymia in patients with BPD. This finding is in accordance with neurophysiological models of alexithymia that implicate a right hemisphere impairment in emotion processing, and could suggest frontal EEG asymmetry as a potential biomarker of relevant psychopathology in these patients.

The effects of gender and depression severity on the association between alpha asymmetry and depression across four brain regions

Data describing the association between EEG asymmetry and depression status have been equivocal. Effects from brain regions involved, depression severity, and the generalisability of findings across genders, have been inconsistently examined and/or verified. This study investigated these issues within a community sample to potentially expand the asymmetry hypothesis to non-severe depression participants. The singular effects of brain region and electrode site, gender, and depression severity, plus the interaction between gender and depression severity across brain regions were investigated in a study of alpha asymmetry among 46 males and 54 females (M age=32.5 yr, SD=14.13 yr) using the Self-rating Depression Scale (Zung, 1973). There was no significant difference across genders or age for depression severity. Dichotomous classification of depressed state produced similar but slightly different results from analysis of the whole range of depression status, although the frontal region was the only area where depression was consistently significantly associated with EEG asymmetry, and then only for females. However, the direction of those differences for females was opposite of that predicted by the EEG asymmetry-depression hypothesis. Several methodological issues that may have contributed to these findings are discussed, with suggestions made for future research that focusses upon individual depression symptom profiles rather than dichotomous or total depression scores in order to assist in developing a clinically-relevant model of EEG asymmetry in depressed persons.

Assessing and conceptualizing frontal EEG asymmetry: An updated primer on recording, processing, analyzing, and interpreting frontal alpha asymmetry

Frontal electroencephalographic (EEG) alpha asymmetry is widely researched in studies of emotion, motivation, and psychopathology, yet it is a metric that has been quantified and analyzed using diverse procedures, and diversity in procedures muddles cross-study interpretation. The aim of this article is to provide an updated tutorial for EEG alpha asymmetry recording, processing, analysis, and interpretation, with an eye towards improving consistency of results across studies. First, a brief background in alpha asymmetry findings is provided. Then, some guidelines for recording, processing, and analyzing alpha asymmetry are presented with an emphasis on the creation of asymmetry scores, referencing choices, and artifact removal. Processing steps are explained in detail, and references to MATLAB-based toolboxes that are helpful for creating and investigating alpha asymmetry are noted. Then, conceptual challenges and interpretative issues are reviewed, including a discussion of alpha asymmetry as a mediator/moderator of emotion and psychopathology. Finally, the effects of two automated component-based artifact correction algorithms-MARA and ADJUST-on frontal alpha asymmetry are evaluated.

Electroencephalogram alpha asymmetry in geriatric depression : Valid or vanished?

BACKGROUND

A correlation between asymmetry in electroencephalographs (EEG) and depression has been demonstrated in many studies. To the best of our knowledge there are no studies including oldest old geriatric patients.

OBJECTIVE

The objective of this study was to evaluate whether frontal and parietal alpha asymmetry can be used to differentiate between depressed and control patients in a cohort sample with a mean age of 80 years.

MATERIAL AND METHODS

Differences in the EEG were investigated in 39 right-handed female geriatric patients (mean age 80 years) with respect to frontal alpha asymmetry (FAA) and parietal alpha asymmetry (PAA) in depression (n = 14), depression combined with anxiety (n = 11) and normal controls (n = 14) as assessed with the hospital anxiety and depression scale (HADS). Band power was calculated for alpha 1 (6.9-8.9 Hz), alpha 2 (8.9-10.9 Hz) and alpha 3 bands (10.9-12.9 Hz). Furthermore, correlations between frontal and parietal alpha asymmetry and the geriatric depression scale (GDS), the HADS and the mini mental state examination (MMSE) were calculated.

RESULTS

A differentiation between the three groups was not possible with FAA and PAA. Significant correlations were found between PAA alpha 3 band and anxiety and depression.

CONCLUSION

The alpha asymmetry in EEG seemed to disappear with age. Correlations between PAA and anxiety and depression were found. The results are in line with the right (hemisphere) hemi-aging hypothesis.

Anticipatory reward deficits in melancholia

Dysfunctional reward processing has long been considered an important feature of major depressive disorder (MDD). However, depression is a heterogeneous construct and the nature of this heterogeneity may contribute to some of the inconsistent empirical findings on reward dysfunction in MDD. The current study examined 1 source of heterogeneity, melancholic symptoms, and its association with reward processing. In individuals with MDD (N = 141) and MDD-free controls (N = 113), electroencephalogram (EEG) alpha asymmetry was measured during a behavioral reward task that probed reward anticipation. Melancholic depression was measured both categorically (Diagnostic and Statistical Manual of Mental Disorders [DSM] diagnosis) and dimensionally (Hamilton Endogenomorphy Scale [HES]). Results showed that a dimensional (and not categorical) definition of melancholia predicted reward processing, with higher melancholic symptoms predicting reduced reward anticipation. Importantly, the effects of melancholic symptoms on reduced reward anticipation remained above and beyond overall depression severity. These results suggest that dysfunctional reward processing may only be associated with melancholic symptoms, not depression in general. (PsycINFO Database Record

The functional role of individual-alpha based frontal asymmetry in stress responding

Asymmetry in frontal electrical activity has been suggested to index tendencies in affective responding and thus may be associated with hormonal stress responses. To assess the functional role of frontal asymmetry (FA) in stress, we measured FA at rest and following exposure to acute stress induced with the Maastricht Acute Stress Task (MAST; N=70) in the standard 8-13Hz band as well as based on individual alpha frequency (IAF) band. IAF-based resting FAF4-F3 was associated with the stress-induced neuroendocrine response, such that left individual frontal activity predicted smaller total cortisol increases in response to the MAST. Like previous studies, we found resting left-sided FAF8-F7 to predict trait behavioural activation measured with the BIS/BAS scales. FA remained unaffected by stress-induced cortisol response. These findings suggest that individual FA might reflect a trait-like characteristic that moderates the stress response. Our results underscore the utility of IAF in studying individual differences in stress responding.