Abnormally slow dynamics in occipital cortex of depression

Aim: Major depressive disorder (MDD) is characterized by altered activity in various higher-order regions like the anterior cingulate and prefrontal cortex. While some findings also show changes in lower-order sensory regions like the occipital cortex in MDD, the latter's exact neural and temporal, e.g., dynamic characterization and symptom severity remains yet unclear. Methods: We conducted resting state fMRI in MDD (N = 49) and healthy controls to investigate the global activity representation of the brain's spontaneous activity in occipital cortex including lower-order (V1) and higher-order (hMT+) regions in the hierarchy of the visual cortex. We further explored (i) these regions' functional connectivity to higher-order prefrontal and subcortical regions, (ii) global signal correlation differences between MDD and controls in different frequency bands, and (iii) their power spectrum's correlation (using median frequency/MF) with symptom severity. Results: Our findings in MDD show: (i) abnormally high functional connectivity of the occipital cortex to both subcortical and higher-order cortical regions; (ii) occipital global signal correlation is reduced mainly in the faster infraslow frequency range (slow 3: 0.073 to 0.198 Hz) as distinguished from the slower ones (slow 5 and 4: 0.01 to 0.027 Hz, and 0.027 to 0.073 Hz); (iii) the reduced neural dynamics in occipital cortex (MF) correlate with the severity of both overall depressive symptoms and psychomotor retardation scores. Conclusions: MDD shows reduced global activity with abnormally slow neural dynamics in occipital cortex that is functionally connected with higher-order regions like the anterior cingulate cortex. The slow dynamics in occipital cortex relates to overall symptom severity and psychomotor retardation.