A neuroimaging study conducted in the Netherlands on individuals with depression has identified brain networks linked to specific cognitive functions. It was further discovered that those with more severe depression symptoms generally exhibit weaker connectivity in the brain network associated with cognitive processing speed. The study was published in Psychological Medicine.
Major Depressive Disorder (MDD), commonly referred to as depression, is a severe mental health condition characterized by a pervasive and prolonged sense of sadness, hopelessness, and a lack of interest or pleasure in activities that were once enjoyable. It leads to a range of emotional and physical symptoms, including feelings of guilt, worthlessness, and helplessness, changes in appetite and sleep patterns, fatigue, difficulty concentrating, and even thoughts of death or suicide.
Studies have indicated that depression impairs cognitive processes such as decision making and attention as well. It also reduces the effectiveness of memory and the processing speed of individuals suffering from it. These cognitive impairments, in turn, exert a toll on individual’s abilities to perform tasks that are part of daily living and work. That is why cognitive impairments are now seen as one of the most important adverse consequences of depression.
Study author Marius Gruber and his colleagues wanted to investigate the changes in brain functioning that underlie cognitive impairments in depression. They reasoned that these changes will likely affect connectivity between areas of the brain responsible for cognitive functioning and that neuroimaging techniques such as diffusion-weighted imaging can be used to capture these characteristics.
Diffusion-weighted imaging (DWI) is an advanced medical imaging technique that charts the erratic motion of water molecules in tissue. This allows the visualization and analysis of white matter tracts in the brain, enabling researchers to make determinations about their functionality.
Earlier studies have shown that individuals with depression often exhibit diminished connectivity in certain brain regions and alterations in white matter structure. The authors of the study posited a potential connection between these cognitive shortcomings and changes in specific networks of connected nerve cells (called connectomes) in the brain.
The study involved 372 individuals experiencing a major depressive episode, 307 MDD patients in remission, and 805 healthy control participants. Women represented two-thirds of the total participants, with the average age ranging from 34 to 37 years. Among those with depression, the average onset age was 26, with most experiencing 3-4 depressive episodes.
Participants underwent magnetic resonance imaging (MRI). The resulting images were statistically analyzed to discern connectomes, which are networks of interconnected brain cells that function together. Cognitive performance was then evaluated using various tests. The results were categorized into processing speed, verbal learning and memory, and executive functioning, including verbal fluency.
The results showed both those with current MDD and MDD patients in remission performed worse than healthy participants on processing speed and verbal fluency tasks. Participants currently in a depressive episode also had worse verbal learning and memory, and worse verbal fluency compared to healthy participants.
All three cognitive domains correlated with markers of connectivity strength. The researchers pinpointed specific brain cell networks associated with each of the cognitive areas. Notably, participants with robust connectivity in these networks typically displayed better cognitive task performance. However, these correlations were relatively weak.
Further analysis revealed that participants in an active depressive state had weaker connectivity within the network linked to processing speed, as compared to their healthy counterparts. Moreover, those with intense depression symptoms exhibited both slower processing speed and weaker connectivity in the relevant brain network.
Summarizing their findings, the authors stated, “Our analyses yielded three main results: First, we replicate findings demonstrating substantial cognitive deficits across various cognitive domains in major depressive disorder. Second, based on network analyses, we show a link between cognitive performance and the structural connectome and present evidence for domain-specific properties of that link. Notably, we found no evidence for differential cognition–connectome associations in healthy and depressed individuals. Instead, our analyses demonstrate structural connectome alterations within cognition-related subnetworks that may be a neurobiological factor underlying cognitive deficits in major depressive disorder.”
The study sheds light on the neural underpinnings of depression-related cognitive impairments. However, it also has limitations that need to be considered. Notably, neuroimaging was done only once. Due to this, it remains unknown whether these neural functioning characteristics are stable or they change over time.
The study, “Cognitive performance and brain structural connectome alterations in major depressive disorder”, was authored by Marius Gruber, Marco Mauritz, Susanne Meinert, Dominik Grotegerd, Siemon C. de Lange, Pascal Grumbach, Janik Goltermann, Nils Ralf Winter, Lena Waltemate, Hannah Lemke, Katharina Thiel, Alexandra Winter, Fabian Breuer, Tiana Borgers, Verena Enneking, Melissa Klug, Katharina Brosch, Tina Meller, Julia-Katharina Pfarr, Kai Gustav Ringwald, Frederike Stein, Nils Opel, Ronny Redlich, Tim Hahn, Elisabeth J. Leehr, Jochen Bauer, Igor Nenadić, Tilo Kircher, Martijn P. van den Heuvel, Udo Dannlowski, and Jonathan Repple.