Cognitive Control Functions in Unipolar Major Depression with and without Co-Morbid Anxiety Disorder

Neuropsychological Assessments of Cognitive Impairment in Major Depressive Disorder: A Systematic Review and Meta-Analysis with Meta-Regression

INTRODUCTION

Cognitive dysfunction or deficits are common in patients with major depressive disorder (MDD). The current study systematically reviews and meta-analyzes multiple domains of cognitive impairment in patients with MDD.

METHODS

PubMed/MEDLINE, PsycINFO, Cochrane Library, Embase, Web of Science, and Google Scholar were searched from inception through May 17, 2023, with no language limits. Studies with the following inclusion criteria were included: (1) patients with a diagnosis of MDD using standardized diagnostic criteria; (2) healthy controls (i.e., those without MDD); (3) neuropsychological assessments of cognitive impairment using Cambridge Neuropsychological Test Automated Battery (CANTAB); and (4) reports of sufficient data to quantify standardized effect sizes. Hedges' g standardized mean differences (SMDs) with corresponding 95% confidence intervals (CIs) were used to quantify effect sizes of cognitive impairments in MDD. SMDs were estimated using a fixed- or random-effects models.

RESULTS

Overall, 33 studies consisting of 2,596 subjects (n = 1,337 for patients with MDD and n = 1,259 for healthy controls) were included. Patients with MDD, when compared to healthy controls, had moderate cognitive deficits (SMD, -0.39 [95% CI, -0.47 to -0.31]). In our subgroup analyses, patients with treatment-resistant depression (SMD, -0.56 [95% CI, -0.78 to -0.34]) and older adults with MDD (SMD, -0.51 [95% CI, -0.66 to -0.36]) had greater cognitive deficits than healthy controls. The effect size was small among unmedicated patients with MDD (SMD, -0.19 [95% CI, -0.37 to -0.00]), and we did not find any statistical difference among children. Cognitive deficits were consistently found in all domains, except the reaction time. No publication bias was reported.

CONCLUSION

Because cognitive impairment in MDD can persist in remission or increase the risk of major neurodegenerative disorders, remediation of cognitive impairment in addition to alleviation of depressive symptoms should be an important goal when treating patients with MDD.

The association between food insecurity and cognitive impairment among the US adults: The mediation role of anxiety or depression

BACKGROUND

Using a nationally representative sample, this study aimed to examine (1) socio-demographic and health-related disparities in cognitive impairment, (2) the association between food insecurity and cognitive impairment, and (3) the mediation role of anxiety or depression in the pathway between food insecurity and cognitive impairment.

METHODS

Cross-sectional data of 28,508 adults from the 2020 National Health Interview Survey were analyzed. Multivariable logistic regression models were used to estimate associations with cognitive impairment. Mediation analyses were conducted using the four-way decomposition method under a counterfactual framework.

RESULTS

Disparities in cognitive impairment were observed across socio-demographic and health-related characteristics (all p < 0.0001). Food insecurity was significantly associated with cognitive impairment in the overall population and the magnitude of the association was greater for the young or middle-aged, females and non-Hispanic Blacks than the general population (AOR ranged from 1.19 to 2.54, all p < 0.01). With anxiety as a mediator, 28.66 % of the total effect of food insecurity on cognitive impairment was attributable to mediation only, and 22.39 % was attributable to interaction (between food insecurity and anxiety) and mediation. With depression as a mediator, 22.33 % of the total effect was attributable to mediation only, and 16.00 % was attributable to interaction (between food insecurity and depression) and mediation.

LIMITATIONS

The cross-sectional design prevents inference of causality.

CONCLUSIONS

Ensuring available and adequate food resources is important to prevent adverse cognitive outcomes. Clinical interventions or treatments for anxiety or depression may help improve cognitive function.

Neurocognitive deficits in depression: a systematic review of cognitive impairment in the acute and remitted state

Previous research suggests a broad range of deficits in major depressive disorder. Our goal was to update the current assumptions and investigate the extent of cognitive impairment in depression in the acute and remitted state. A systematic review of the existing literature between 2009 and 2019 assessing the risk of bias within the included studies was performed. Of the 42 articles reviewed, an unclear risk of bias was shown overall. The risk of bias mainly concerned the sample selection, inadequate remedial measures, as well as the lack of blinding the assessors. In the acute phase, we found strong support for impairment in processing speed, learning, and memory. Follow-up studies and direct comparisons revealed less pronounced deficits in remission, however, deficits were still present in attention, learning and memory, and working memory. A positive correlation between the number of episodes and cognitive deficits as well as depression severity and cognitive deficits was reported. The results also demonstrate a resemblance between the cognitive profiles in bipolar disorder and depression. Comparisons of depression with schizophrenia led to unclear results, at times suggesting an overlap in cognitive performance. The main findings support the global deficit hypothesis and align with results from prior meta-analyses and reviews. Recommendations for future research are also presented.

Assessment of Objective and Subjective Cognitive Function in Patients With Treatment-Resistant Depression Undergoing Repeated Ketamine Infusions

BACKGROUND

Subanesthetic ketamine infusions can elicit rapid and sustained antidepressant effects, yet the potential cognitive impact of ketamine has not been thoroughly examined. This study measured changes in objective and subjective cognitive function following repeated ketamine treatment.

METHODS

Thirty-eight patients with treatment-resistant depression were administered cognitive assessments before and after undergoing 7 i.v. ketamine infusions (0.5 mg/kg over 40 minutes) within a clinical trial examining the efficacy of single and repeated administrations. Depression severity and perceived concentration were evaluated with the Montgomery-Åsberg Depression Rating Scale (MADRS) and the Quick Inventory of Depressive Symptoms Self-Report.

RESULTS

Twenty-three participants (60.5%) responded after repeated infusions (≥50% decrease in MADRS total scores). We measured significant improvements in several cognitive domains, including attention, working memory, verbal, and visuospatial memory (effect sizes ranging from Cohen d = 0.37-0.79). Cognitive changes were attributed to reduction in depressive symptoms except for improvement in verbal memory, which remained significant after adjustment for change in MADRS total score (P = .029, η p2 = 0.13). Only responders reported improvement in subjective cognitive function with repeated ketamine administration (MADRS item 6, P < .001, d = 2.00; Quick Inventory of Depressive Symptoms Self-Report item 10, P < .001, d = 1.36).

CONCLUSION

A short course of repeated ketamine infusions did not impair neurocognitive function in patients with treatment-resistant depression. Further research is required to understand the potential mediating role of response and remission on improved cognitive function accompanying ketamine treatment as well as to examine longer-term safety outcomes. ClinicalTrials.gov identifier NCT01945047.

Impairment of response inhibition to emotional face stimuli in individuals with subclinical depression

Response inhibition, a crucial component of executive function, is closely related to personal impulse control, social adaption, and mental health. Previous studies have found response inhibition deficit in patients with major depressive disorder, but whether it also exists in individuals with subclinical depression (SD) remains unclear. This study aimed to identify the ability of response inhibition to emotional face stimuli both under explicit and implicit conditions in individuals with SD. Thirty-six subclinical depressed college students and 39 healthy individuals were recruited and administered the non-emotional, explicit, and implicit emotional stop-signal tasks (SSTs). Mixed-model analyses of variance were used to analyze the differences between and within groups. In implicit emotional SST, the results showed a significant longer stop-signal response time, a shorter stop-signal delay time, a shorter go reaction time, and a similar proportion of stop success in the SD group compared to healthy controls. However, the above indices showed no significant difference between the two groups in the non-emotional SST and explicit emotional SST. These findings suggest a possible defect of response inhibition in implicit emotional processing in individuals with SD, which may potentially serve as a marker of susceptibility to depression and thus be applied to early screening and intervention for major depressive disorder.

Frozen in (e)motion: How reactive motor inhibition is influenced by the emotional content of stimuli in healthy and psychiatric populations

Efficient inhibitory control is vital. However, environmental cues can influence motor control especially in an emotional context. One common task to measure inhibitory control is the stop-signal task (SST), which asks participants to respond to go stimuli knowing that on some trials a stop signal will be presented, requiring them to inhibit their response. This paradigm estimates the ability to inhibit already-initiated responses by calculating participants' stop-signal reaction times (SSRT), an index of inhibitory control. Here, we aim to review the existing, often contradictory, evidence on the influence of emotional stimuli on the inhibitory process. We aim to discuss which factors may reveal an interference as well as an advantage of emotional stimuli on action inhibition performance. Finally, we review the existing evidence that has investigated the effect of such stimuli on action inhibition in the psychiatric population. Important factors are the relevance, the intensity and the valence of the emotional stimulus, as well as the affected component of the motor control. From all this evidence, it is clear that understand precisely how emotion is integrated into core executive functions, such as inhibitory control, is essential not only for cognitive neuroscience, but also for refining neurocognitive models of psychopathology.

Plasma metabolites were associated with spatial working memory in major depressive disorder

Major depressive disorder (MDD) is a common disease with both affective and cognitive disorders. Alterations in metabolic systems of MDD patients have been reported, but the underlying mechanisms still remains unclear. We sought to identify abnormal metabolites in MDD by metabolomics and to explore the association between differential metabolites and neurocognitive dysfunction.Plasma samples from 53 MDD patients and 83 sex-, gender-, BMI-matched healthy controls (HCs) were collected. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) system was then used to detect metabolites in those samples. Two different algorithms were applied to identify differential metabolites in 2 groups. Of the 136 participants, 35 MDD patients and 48 HCs had completed spatial working memory test. Spearman rank correlation coefficient was applied to explore the relationship between differential metabolites and working memory in these 2 groups.The top 5 metabolites which were found in sparse partial least squares-discriminant analysis (sPLS-DA) model and random forest (RF) model were the same, and significant difference was found in 3 metabolites between MDD and HCs, namely, gamma-glutamyl leucine, leucine-enkephalin, and valeric acid. In addition, MDD patients had higher scores in spatial working memory (SWM) between errors and total errors than HCs. Valeric acid was positively correlated with working memory in MDD group.Gamma-glutamyl leucine, leucine-enkephalin, and valeric acid were preliminarily proven to be decreased in MDD patients. In addition, MDD patients performed worse in working memory than HCs. Dysfunction in working memory of MDD individuals was associated with valeric acid.

The effectiveness of intravenous ketamine in adults with treatment-resistant major depressive disorder and bipolar disorder presenting with prominent anxiety: Results from the Canadian Rapid Treatment Center of Excellence

BACKGROUND

Individuals meeting criteria for treatment-resistant depression (TRD) are differentially affected by high levels of anxiety symptoms.

AIMS

There is a need to identify the efficacy of novel rapid-onset treatments in adults with mood disorders and comorbid anxious-distress.

METHODS

This study included patients with treatment-resistant major depressive disorder (MDD) or bipolar disorder (BD) who were receiving intravenous (IV) ketamine treatment at a community-based clinic.Anxious-distress was proxied using items from the Quick Inventory of Depressive Symptomatology-Self Report 16-item (QIDS-SR₁₆) and Generalized Anxiety Disorder 7-item (GAD7) scales. The difference in QIDS-SR₁₆ total score, QIDS-SR₁₆ suicidal ideation (SI) item and GAD7 score were analyzed between groups.

RESULTS

A total of 209 adults with MDD (n = 177) and BD (n = 26) were included in this analysis. From this sample, 94 patients (mean = 45 ± 13.9 years) met the criteria for anxious-distress. Individuals meeting the criteria for anxious-distress exhibited a significantly greater reduction in QIDS-SR₁₆ total score following four infusions (p = 0.02) when compared with patients not meeting the anxious-distress criteria. Both anxious-distressed and low-anxiety patients exhibited a significant reduction in SI (p < 0.0001) following four infusions.Finally, there was a significantly greater reduction in anxiety symptoms in the anxious-distress group compared with the non-anxious distress group following three (p = 0.02) and four infusions (p < 0.001).

CONCLUSION

Patients with TRD and prominent anxiety receiving IV ketamine exhibited a significant reduction in depressive, SI and anxiety symptoms.

A Longitudinal 5-Year Follow-Up Study of Cognitive Function After First Episode Major Depressive Disorder: Exploring State, Scar and Trait Effects

Major depression (MDD) is associated with cognitive deficits in processing speed and executive function (EF) following first episode (FE). It is unclear whether deficits are state or trait related. Studies following FE MDD over longer periods are lacking, making it uncertain how cognition and symptoms develop after the initial episode. The present study assessed cognitive function and symptoms 5 years following FE MDD. In addition, the study explored relationships between MDD symptoms, rumination, and cognitive deficits with regards to the trait, state, and scar perspective. Twenty-three participants with previous FE MDD, and 20 matched control participants were compared on Delis-Kaplan Executive Function System measures of processing speed and EF, in a 5-year longitudinal follow-up study. Correlations between current symptoms- and history of MDD, rumination, cognition were investigated. Findings indicated that cognitive deficits persisted with no clear signs of exacerbation after initial episode. Inhibition appeared independent of current and previous symptoms of depression. Processing speed was related to depressive- symptoms and rumination. In conclusion, results indicated persisting, stable deficits in both EFs and processing speed. Findings further suggest that depressive symptoms could be related to deficits in processing speed, indicating state effects. There was limited support for worsening of cognition after initial episode. Some aspects of EF like Inhibition could show persistent deficits independent of depressive symptoms indicating trait effects.

Verbal memory predicts treatment outcome in syndromal anxious depression: An iSPOT-D report

BACKGROUND

Major Depressive Disorder (MDD), anxiety disorders, and high levels of anxious symptoms are associated with impaired cognitive functioning. However, little is known of how cognitive functioning is impaired in people with anxious depression. Here, we compared cognitive functioning between people with anxious depression, non-anxious depression, and healthy controls. We also tested whether anxious depression moderated the relationship between cognitive functioning and treatment outcome.

METHODS

1008 adults with MDD and 336 healthy controls completed IntegNeuro: a computerized cognitive functioning test battery. Participants were then randomised to one of three antidepressants and reassessed at 8 weeks using the 17-item Hamilton Depression Rating Scale (HRSD₁₇) and the 16-Item Quick Inventory of Depressive Symptomatology-Self-Rated for remission and response. Syndromal anxious depression was defined as MDD with a comorbid anxiety disorder. HRSD anxious depression was defined as MDD with a comorbid HRSD₁₇ anxiety/somatisation factor score ≥ 7.

RESULTS

Syndromal anxious depression was associated with better psychomotor functioning and poorer working memory, cognitive flexibility and information processing speed compared to their non-anxious counterparts. HRSD anxious depression was associated with better psychomotor functioning compared to their non-anxious counterparts. Syndromal anxious depression moderated the relationship between verbal memory and treatment outcome. In people with syndromal anxious depression, poorer baseline verbal memory predicted poorer treatment outcome.

LIMITATIONS

As DSM-IV criteria was used, the DSM-5 anxious distress specifier characterisation of anxious depression could not be assessed CONCLUSIONS: Syndromal anxious depression is characterised by impaired executive functions and moderates the relationship between verbal memory functioning and treatment outcome.

Influence of comorbid anxiety symptoms on cognitive deficits in patients with major depressive disorder

BACKGROUND

Major depressive disorder (MDD) patients with comorbid anxiety symptoms showed obvious cognitive deficits. However, it remains unclear whether comorbid anxiety symptoms will make a specific contribution to cognitive deficits in MDD.

METHODS

Executive function, processing speed, attention and memory were assessed in 162 MDD patients, and 142 healthy controls (HCs) by a comprehensive neuropsychological battery. 14-item Hamilton Anxiety Rating Scale (HAM-A) was used for anxiety symptoms and MDD patients with HAM-A total score >14 were classified into MDD with comorbid anxiety (MDDA) group. A multivariate analysis of covariance and regression models was conducted to evaluate the effects of anxiety symptoms on cognitive deficits.

RESULTS

There were no significantly differences in all 4 cognitive domains between MDD alone and MDDA patients (all p < 0.05). In MDDA subgroup, HAM-A total score contributed to executive function and memory (both p < 0.05), while HAM-A psychic symptoms contributed to all 4 domains (all p < 0.05). Moreover, after controlling for the severity of depression, either anxiety symptoms shown as HAMA total score or psychic anxiety symptoms only contributed significantly to the executive function performance.

LIMITATIONS

The cross-sectional design made it hard to acquire a cognitive performance trajectory accompanied by the fluctuations in anxiety symptoms.

CONCLUSION

Our findings suggest that there is no significant difference in cognitive performance between MDD alone and MDDA patients. However, comorbid anxiety, especially psychic anxiety may contribute to extensive cognitive deficits in MDDA patients. Notably, anxiety symptoms only independently triggered executive dysfunction when eliminating effect of the severity of depression.

The emotion regulation effect of cognitive control is related to depressive state through the mediation of rumination: An ERP study

Deficits in cognitive control have been found in depression, but how they contribute to depressive symptoms remains unknown. The present study investigated whether the regulatory efficacy of cognitive control on negative emotion varies with depression level and whether the regulatory efficacy affects depressive symptoms via the mediation of rumination. Fifty participants screened by the Zung Self-Rating Depressive Scale (SDS) with high and low depression levels were selected. They were instructed to controlled-process different semantic representations of aversive pictures, and the amplitude of the late positive potential (LPP) evoked by the pictures was used as the measure of electrocortical response. We found that controlled-processing neutral representations of aversive pictures significantly decreased the amplitude of LPP relative to that under controlled-processing unpleasant ones in an early window in the low depression group and that this regulatory effect was impaired in the high depression group. Furthermore, a mediation analyses indicated that the regulatory efficacy of controlled-processing different semantic representations was associated with SDS score via the mediation of rumination. These findings shed light on the mechanisms underlying the association between the function of cognitive control in emotion generation and depressive symptoms and indicated a pathway from the regulatory efficacy of cognitive control to depression via rumination.

Exploration of Major Cognitive Deficits in Medication-Free Patients With Major Depressive Disorder

Background: Major depressive disorder (MDD) is associated with a wide range of cognitive deficits. However, it remains unclear whether there will be a major cognitive deficit independently caused by depression at acute episodes of MDD. Method: A comprehensive neurocognitive test battery was used to assess the executive function, processing speed, attention, and memory in 162 MDD patients and 142 healthy controls (HCs). A multivariate analysis of variance, hierarchical regression analyses and general linear regression analyses were used to explore the possible major cognitive deficits and their predictor variables. Results: MDD patients showed extensive impairment in all four cognitive domains. Impairment of executive function and processing speed were found to persist even with other cognitive domains and clinical variables being accounted for. Executive function and processing speed were further predicted by total disease duration and depression severity, respectively. Conclusions: Executive function and processing speed may be two distinct major deficits at acute episodes of MDD. Furthermore, the executive function is likely originated from the cumulative effect of disease duration and processing speed is possibly derived from the temporary effect of current depressive episode.

Correlations between working memory impairment and neurometabolites of prefrontal cortex and lenticular nucleus in patients with major depressive disorder

BACKGROUND

The mechanism of working memory (WM) impairment in MDD remains unclear. We aimed to find out the mechanism by using neuropsychological tests and proton magnetic resonance spectroscopy (1H-MRS).

METHODS

31 MDD patients and 31 healthy controls were recruited in our study. The WM performance and neurometabolite ratios of prefrontal cortex (PFC) and lenticular nucleus (LN) between two groups were evaluated and compared. And the correlations between abnormal neurometabolite ratios and WM dysfunction were computed.

RESULTS

Scores of SDMT, DST(forwards), VRS and 2-back Task(accuracy rate) in MDD were lower than HCs. NAA/Cr ratios of bilateral PFC in MDD were significantly lower than HCs, while no significant differences showed in NAA/Cr ratios of LN and Cho/Cr, mI/Cr values of the bilateral PFC and LN between two groups. And for MDD patients, NAA/Cr ratios in the right PFC were positively correlated with scores of DST (Forwards).

CONCLUSIONS

Our findings suggest that depressed patients may have impairments in working memory, including phonological loop, visual-spatial sketchpad, episodic buffer and central executive. And the impairment of verbal WM and WM capacity may be associated with the abnormal neurometabolites in the right PFC.

Impact of anxiety on prefrontal cortex encoding of cognitive flexibility

Anxiety often is studied as a stand-alone construct in laboratory models. But in the context of coping with real-life anxiety, its negative impacts extend beyond aversive feelings and involve disruptions in ongoing goal-directed behaviors and cognitive functioning. Critical examples of cognitive constructs affected by anxiety are cognitive flexibility and decision making. In particular, anxiety impedes the ability to shift flexibly between strategies in response to changes in task demands, as well as the ability to maintain a strategy in the presence of distractors. The brain region most critically involved in behavioral flexibility is the prefrontal cortex (PFC), but little is known about how anxiety impacts PFC encoding of internal and external events that are critical for flexible behavior. Here we review animal and human neurophysiological and neuroimaging studies implicating PFC neural processing in anxiety-induced deficits in cognitive flexibility. We then suggest experimental and analytical approaches for future studies to gain a better mechanistic understanding of impaired cognitive inflexibility in anxiety and related disorders.

Influence of anxiety symptoms on improvement of neurocognitive functions in patients with major depressive disorder: A 12-week, multicenter, randomized trial of tianeptine versus escitalopram, the CAMPION study

BACKGROUND

Previous research has reported evidence that patients with major depressive disorder (MDD) show anxiety symptoms and neurocognitive impairments. However, the influence of anxiety on neurocognitive function in MDD patients during antidepressant treatment is unclear.

METHOD

MDD patients (n=164) completed a 12-week, multicenter, randomized trial assigned in a 1:1 ratio to either tianeptine or escitalopram. Changes of anxiety symptoms were assessed by the Hamilton Anxiety Rating Scale (HAM-A), and the Hamilton Depression Rating Scale (HAM-D), self-rated subjective cognitive impairment on memory and concentration, the Mini-Mental Status Examination (MMSE), Continuous Performance Test (CPT), Verbal Learning Test (VLT), and Raven's Progressive Matrices (RPM) were assessed every 4 weeks.

RESULTS

During 12 weeks of treatment, decrease in the HAM-A score was significantly associated with improvement of subjective cognitive impairments on memory (p<0.001) and concentration (p<0.001), and objective measures on delayed memory (p=0.006) and reasoning ability (p=0.002), after adjusting for covariates such as baseline HAM-A scores, time, sex, age, education years and assigned medication using the Mixed effects and Generalized Estimated Equation model analysis. However, the other cognitive outcome variables, immediate memory, commission error, and MMSE, which showed significant improvement through 12-week study period, showed no significant association with improvement of anxiety.

CONCLUSION

Improvement of anxiety symptoms was significantly associated with improvement in subjective and objective neurocognitive functions such as delayed memory and reasoning ability in elderly MDD patients during antidepressant treatment, but not significantly associated with improvement of immediate memory and commission error.

TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT01309776.

Cognitive performance improvement in Canadian Armed Forces personnel during deployment

Introduction: Chronic stress can decrease resilience and diminish cognitive adaptability; thus, operational stressors related to military deployment can pose significant risks to cognitive functioning. Numerous studies have aimed to assess the effects of deployment on cognitive functioning on the basis of cognitive performance measures administered before and after deployment. However, to the best of our knowledge, no studies have measured neurocognitive performance of military personnel while they were deployed to a combat zone. Methods: Canadian Armed Forces military troops ( N = 85) were tested during pre-deployment training and during deployment in Afghanistan. At both time points, the participants completed a detailed demographic form and performed touch-screen neurocognitive tests using the Cambridge Neuropsychological Test Automated Battery (CANTAB). The CANTAB measurements included executive function (Attention Switching Task [AST] and Spatial Working Memory [SWM] test), decision making and response control (Stop Signal Task [SST]), and attention (Reaction Time [RTI] test). Two-tailed, paired t-tests were used to compare pre-deployment and deployment CANTAB results. Results: On average, all participants significantly improved their performance on all neurocognitive tests during deployment compared with pre-deployment. At both pre-deployment and deployment time points, the participants demonstrated excellent performance on the AST and RTI test and less-than-optimal performance on the SWM test and SST. Discussion: The influence of training, social factors, and emotional status, among many others, on cognitive adaptability should be taken into account to fully understand soldiers’ capability to improve and maintain high cognitive functioning during deployment.

Cognitive impairment in depression: a systematic review and meta-analysis

BACKGROUND

This review aimed to address the question of whether cognitive impairment should be considered a core feature of depression that may be a valuable target for treatment.

METHOD

We conducted a systematic review and meta-analysis of cognitive function, assessed with a single neuropsychological test battery, the Cambridge Neuropsychological Test Automated Battery (CANTAB), in patients with depression during symptomatic and remitted states. Inclusion of studies comparing patients remitted from depression and controls enabled us to investigate whether cognitive impairment persists beyond episodes of low mood in depression.

RESULTS

Our meta-analysis revealed significant moderate cognitive deficits in executive function, memory and attention in patients with depression relative to controls (Cohen's d effect sizes ranging from -0.34 to -0.65). Significant moderate deficits in executive function and attention (Cohen's d ranging from -0.52 to -0.61) and non-significant small/moderate deficits in memory (Cohen's d ranging from -0.22 to -0.54) were found to persist in patients whose depressive symptoms had remitted, indicating that cognitive impairment occurs separately from episodes of low mood in depression.

CONCLUSIONS

Both low mood and cognitive impairment are associated with poor psychosocial functioning. Therefore, we argue that remediation of cognitive impairment and alleviation of depressive symptoms each play an important role in improving outcome for patients with depression. In conclusion, this systematic review and meta-analysis demonstrates that cognitive impairment represents a core feature of depression that cannot be considered an epiphenomenon that is entirely secondary to symptoms of low mood and that may be a valuable target for future interventions.