Virtual image grasping in patients with Alzheimer-type dementia.

Patients with various neuropsychiatric disorders who confused virtual images with real objects have recently been described. When asked to take objects from an investigator's hand while looking in a mirror, these patients reached directly into the mirror for the object's image. To investigate whether the phenomenon occurs in patients with Alzheimer's disease, we studied 127 cases, of whom 67 were suspected of having Alzheimer-type dementia (DAT). The phenomenon in question was not observed in either of two control groups, but whereas 38 (57%) of the DAT patients responded correctly, 17 (25%) of them grasped at the mirror image. Characteristically, none of the eight patients who grasped into the mirror and underwent single photon emission computed tomography analysis showed symmetric activity. We also analyzed the behaviour and verbal utterances of the DAT patients in front of the mirror.