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.