A 39-year-old man who has played guitar for pleasure most evenings for twenty years continues to pick it up out of habit, but reports that it now feels like going through empty motions, with none of the satisfaction or enjoyment it used to bring him, no matter how long he plays. What is this?

This is anhedonia: a loss of the capacity to feel pleasure specifically, even while still engaging in a once-enjoyed activity. It is not apathy, which concerns reduced motivation and interest more broadly — he is still motivated enough to pick up the guitar, but gets no pleasure from it once he does. It is not simple boredom, which would be a passing, situational loss of interest rather than a persistent inability to feel pleasure from something previously reliable. And it is not psychomotor retardation, which concerns a physical slowing of movement and thought, not the felt quality of pleasure.