Global Burden of Disease 2017 estimates for Major Depressive Disorder: a critical appraisal of the epidemiological evidence

Intracranial Directed Connectivity Links Subregions of the Prefrontal Cortex to Major Depression

Understanding the neural basis of major depressive disorder (MDD) is vital to guiding neuromodulatory treatments. The available evidence supports the hypothesis that MDD is fundamentally a disease of cortical disinhibition, where breakdowns of inhibitory neural systems lead to diminished emotion regulation and intrusive ruminations. Recent research also points towards network changes in the brain, especially within the prefrontal cortex (PFC), as primary sources of MDD etiology. However, due to limitations in spatiotemporal resolution and clinical opportunities for intracranial recordings, this hypothesis has not been directly tested. We recorded intracranial EEG from the dorsolateral (dlPFC), orbitofrontal (OFC), and anterior cingulate cortices (ACC) in neurosurgical patients with MDD. We measured daily fluctuations in self-reported depression severity alongside directed connectivity between these PFC subregions. We focused primarily on delta oscillations (1-3 Hz), which have been linked to GABAergic inhibitory control and intracortical communication. Depression symptoms worsened when connectivity within the left vs. right PFC became imbalanced. In the left hemisphere, all directed connectivity towards the ACC, from the dlPFC and OFC, was positively correlated with depression severity. In the right hemisphere, directed connectivity between the OFC and dlPFC increased with depression severity as well. This is the first evidence that delta oscillations flowing between prefrontal subregions transiently increase intensity when people are experiencing more negative mood. These findings support the overarching hypothesis that MDD worsens with prefrontal disinhibition.

Global Burden Disease Estimates for Major Depressive Disorders (MDD): A review of diagnostic instruments used in studies of prevalence

Global Burden of Disease (GBD) estimates have significant policy implications nationally and internationally. Disease burden metrics, particularly for depression, have played a critical role in raising governmental awareness of mental health and in calculating the economic cost of depression. Recently, the World Health Organization ranked depression as the single largest contributor to global disability. The main aim of this paper was to assess the basis upon which GBD prevalence estimates for major depressive disorder (MDD) were made. We identify the instruments used in the 2019 GBD estimates and provide a descriptive assessment of the five most frequently used instruments. The majority of country studies, 356/566 (62.9%), used general mental health screeners or structured/semi-structured interview guides, 98/566 (17.3%) of the studies used dedicated depression screeners, and 112 (19.8%) used other tools for assessing depression. Thus, most of the studies used instruments that were not designed to make a diagnosis of depression or assess depression severity. Our results are congruent with and extend previous research that has identified critical flaws in the data underpinning the GBD estimates for MDD. Despite the widespread promotion of these prevalence estimates, caution is needed before using them to inform public policy and mental health interventions. This is particularly important in lower-income countries where resources are scarce.

Industry influence on mental health research: depression as a case example

Emotional distress has been rising since before the COVID-19 pandemic and the public is told that depression is a major public health problem. For example, in 2017 depressive disorders were ranked as the third leading cause of "years lost to disability" and the World Health Organization now ranks depression as the single largest contributor to global disability. Although critical appraisals of the epidemiological data raise questions about the accuracy of population-based depression estimates, the dominance of the medical model and the marketing of psychotropics as "magic bullets," have contributed to a dramatic rise in the prescription of psychiatric drugs. Unfortunately, the pharmaceutical industry's influence on psychiatric research and practice has resulted in over-estimates of the effectiveness of psychotropic medications and an under-reporting of harms. This is because the principles that govern commercial entities are incongruent with the principles that guide public health research and interventions. In order to conduct mental health research and develop interventions that are in the public's best interest, we need non-reductionist epistemological and empirical approaches that incorporate a biopsychosocial perspective. Taking depression as a case example, we argue that the socio-political factors associated with emotional distress must be identified and addressed. We describe the harms of industry influence on mental health research and show how the emphasis on "scaling up" the diagnosis and treatment of depression is an insufficient response from a public health perspective. Solutions for reform are offered.

Consolidating evidence on the role of insulin resistance in major depressive disorder

PURPOSE OF REVIEW

The circular interactions between type 2 diabetes (TMD2) and major depressive disorder (MDD) are well documented but the understanding of their mechanisms has only recently gained more clarity. Latest research indicates, that the association between TMD2 and MDD is largely mediated by insulin resistance (IR).

RECENT FINDINGS

A metabolic subtype of MDD can be distinguished from other MDD subpopulations, that is characterized by predominantly atypical clinical presentation, IR and different responsiveness to antidepressant interventions. IR is a predictor of nonresponse to some antidepressants. The IR seems to be a state-marker of clinical or subclinical depression and the relationship between IR and MDD varies between sexes and ethnicities. Insulin has a direct impact on the monoaminergic systems known to underlie MDD symptoms: serotoninergic and dopaminergic, which are dysregulated in IR subjects. Several trials assessed the efficacy of insulin-sensitizing drugs in MDD with mixed results for metformin and more consistent evidence for pioglitazone and lifestyle intervention/physical activity.

SUMMARY

Recently published data suggest a significant role of IR in the clinical presentation, pathophysiology and treatment response in MDD. Further research of IR in MDD and integration of existing data into clinical practice are needed.