Cognitive difficulties, including problems with attention and executive processing, are common in major depressive disorder (MDD), and strongly predict psychosocial and occupational functioning. Impairment in sustained attention contributes to increased intra-individual variability (IIV) in reaction times observed during cognitive tasks. Understanding brain network changes associated with IIV could guide novel neuromodulation strategies targeting cognitive difficulties.

We analyzed baseline resting-state fMRI data from 209 patients with moderate-to-severe treatment-resistant MDD who participated in the BRIGhTMIND neuromodulation trial. Following a preregistered analytic protocol, we examined associations between: functional connectivity across three core brain networks (executive control, ECN; default mode, DMN; and salience network, SN); components of IIV derived from a choice reaction time task (using a three-parameter ex-Gaussian model); and functioning.

Greater IIV was linked to increased ECN-DMN functional connectivity. The ECN supports top-down control and externally directed cognition, while the DMN supports internal mentation and rumination. ECN-DMN connectivity was modulated by the SN, which prioritizes salient internal and external stimuli. Higher SN-ECN connectivity was associated with lower ECN-DMN connectivity and with faster mean reaction times. Both IIV and mean reaction time predicted functioning, with poorer functioning related to a slowed and inflexible response pattern.

Distinct components of reaction time variability are associated with specific patterns of brain network connectivity, largely independent of mood severity. Connectivity between the salience and executive control networks may represent a promising target for neuromodulation interventions focused on cognitive deficits in MDD.

To evaluate social and occupational functioning in patients in partial remission (PR) compared with patients in complete remission (CR) of a major depressive disorder (MDD) episode.

This is a six-month prospective study. PR was defined as a score more than 7 and less or equal to 15 in the Hamilton Depression Rating Scale, and CR as less or equal to 7. All patients had been on acute antidepressant treatment during the previous three months and no longer met criteria for MDD. Functioning was assessed by the Social and Occupational Functioning Assessment Scale (SOFAS).

Mean (S.D.) patient age was 50.5 (14.5) years (N = 292) and 77% were female. At baseline, partial remitters showed greater impairment in social and occupational functioning than complete remitters (62.8 [12.6] versus 80.4 [10.5], respectively; P < .0001). After six months, only 47% PR versus 77% CR reached normal functioning, and SOFAS ratings for PR were below normal range (76.2 [12.3] PR versus 84.6 [9.4] CR; P < .0001). PR reported three times more days absent from work due to sickness than CR (63 days versus 20 days; P < .001).

We conclude that PR of an MDD episode is associated with significant functional impairment that persists even after nine months of antidepressant treatment. Our results underline the importance of treating the patient until achieving full remission.