Penning article, purist's shattered mentally (8)
I believe the answer is:
upstairs
'mentally' is the definition.
(as in not having much going on upstairs)
'penning article purist's shattered' is the wordplay.
'penning' is an insertion indicator.
'article' becomes 'a' (English indefinite article).
'shattered' is an anagram indicator.
'purists' is an anagram of 'upstirs'.
'a' put into 'upstirs' is 'UPSTAIRS'.
(Other definitions for upstairs that I've seen before include "In the top half of a house" , "On the next floor" , "flight" , "Above ground floor" , "On an upper floor" .)