Ramachandran's theory was challenged by a 2010 research study conducted by Marian Michielsen of the University Medical Center, Rotterdam. Michielsen carried out research involving 22 stroke victims which suggests that mirror therapy works by enhancing the spatial coupling between limbs. Michielsen stated that "The hypothesis that the mirror illusion enhances spatial coupling is supported by studies on healthy volunteers, showing that the mirror illusion increased the tendency of one limb to take on the spatial properties of the other limb (Michielsen et al.