Billions with deep depression - it's integral to minds (8)

'minds' is the definition.
The answer and definition can be both to do with social activities as well as being verbs in their -s form.
Maybe they are linked in a way I don't understand?

'billions with deep depression it's integral' is the wordplay.
I cannot really understand how this works, but
'billions' could be 'b' (abbreviation) and 'b' is found within the answer.
'with' could be 'by' (both can mean close together) and 'by' is present in the answer.
'it's' could be 'ts' (abbreviation. e.g. in 'tis) and 'ts' is found in the answer.
The remaining letters 'asi' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'to' acts as a link.

Can you help me to learn more?