Cingulate cortex hyper metabolic activity, a paradox?

Galteeth

Hyperactivity in the anterior cingulate cortex (brodmann area 25) is correlated with depression. Increased glucose metabolism has been observed, yet decreases in gray matter have also been observed. Does anyone know why this is (or know similar instances of increased glucose use combined with loss of grey matter), or could someone provide links to an informative source?