for those wondering what Behavioral Activation is, here is a link to a scholarly paper, full of words.

Behavioural activation for depression | BJPsych Advances

essentially, the paper says, BA was originally a component of Cognitive Behavioral Therapy. it can also be practiced alone:

"Behavioural activation is grounded in learning theory and contextual functionalism. It is not about scheduling pleasant or satisfying events (as in the first stage of cognitive therapy). It does not focus on an internal cause of depression such as thoughts, inner conflicts or serotonergic dysfunction. The focus is on the whole event and variables that may influence the occurrence of unhelpful responses – both overt behaviour and cognitive processes."

hope this helps to clarify new terms~
Gus