Behavioral interventions for depression may lose effectiveness beyond a certain volitional threshold where individuals experience difficulty controlling thoughts and motor functions.

“There seems to be a volitional threshold for depression where at some point you start losing, you go from being completely in total volition to having kind of semi-volition. You have thoughts that you really have a hard time controlling and that sort of thing. And when you go through that threshold, at some point it gets harder and harder for those sorts of things to kind of kick in and work. And the extreme form of that is catatonia, right? Where people in a very severe form of depression get kind of stuck motorically, right? And they obviously can't, they have no control or very limited control.”