Beat no longer, reaching edge of consciousness (9)
I believe the answer is:
threshold
'edge of consciousness' is the definition.
(as in the threshold of consciousness)
'beat no longer' is the wordplay.
'beat' becomes 'thresh' (threshing is a kind of beating).
'no longer' becomes 'old' (both can mean former).
'thresh'+'old'='THRESHOLD'
'reaching' is the link.
(Other definitions for threshold that I've seen before include "Verge" , "Doorstep" , "Lower limit" , "Doorway, entrance" , "gate" .)