Neither does the T-1000 but that doesnt stop it from getting Stunned from attacks.
Stunning has nothing to do with 'brains'. That's concussion.
Stunning is defined in the OED as being ' so shocked that one is temporarily unable to react; astonished' and it includes being 'Dazed, Staggered, Shocked, Startled or Overwhelmed', and all of those things can happen to a robot or construct, and indeed do happen to them in movies and literature all the time.
Frankenstiens monster is a flesh golem dude.
Bits of other bodies, stitched together, animated by electricity and capable of going berserk.