Anterior-posterior gradient differences in lobar and cingulate cortex cerebral blood flow in late-life depression

Vascular pathology is common in late-life depression, contributing to changes in cerebral function. We examined whether late-life depression was associated with differences in cerebral blood flow (CBF) and whether such differences were related to vascular risk and cerebrovascular pathology, specifically white matter hyperintensity (WMH) volumes. Twenty-three depressed elders and 20 age- and sex-matched elders with no psychiatric history completed cranial 3T MRI. MRI procedures included a pseudo-continuous Arterial Spin Labeling (pcASL) acquisition obtained while on room air and during a hypercapnia challenge allowing for calculation of cerebrovascular reactivity (CVR). Brain segmentation identified frontal, temporal, parietal and cingulate sub-regions in which CBF and CVR were calculated. The depressed group exhibited an anterior-posterior gradient in CBF, with lower CBF throughout the frontal lobe but higher CBF in the parietal lobe, temporal lobe, thalamus and hippocampus. A similar anterior to posterior gradient was observed in the cingulate cortex, with anterior regions exhibiting lower CBF and posterior regions exhibiting higher CBF. We did not observe any group differences in CVR measures. We did not observe significant relationships between CBF and CVR with vascular risk or WMH volumes, aside from an isolated finding associating higher WMH volumes with lower CBF in the rostral anterior cingulate cortex. Decreased anterior CBF in depressed elders might reflect decreased metabolic activity in these regions, while increased posterior CBF may represent either compensatory processes or different activity of posterior intrinsic functional networks. Future work should examine how these findings are related to compensatory changes with aging.