From online article "Nighttime lights linked to depression"
http://www.msnbc.msn.com/id/40242387/ns/health-mental_health

"In people, loss of enjoyment is known as anhedonia and is a major symptom of depression."

From http://www.etymonline.com/, the 3 parts of "anhedonia" are Greek.
an- without
hedone pleasure
-ia to form an abstract feminine gender noun

They have the actual word at that site, but it doesn't break out the -ia.

Anyway, the article is intriguing, even if applying the results to humans seems a little premature.