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.