Mirror agnosia and mirror ataxia constitute different parietal lobe disorders

We describe two new clinical syndromes, mirror agnosia and mirror ataxia, b oth characterized by the deficit of reaching for an object through a mirror in association with a lesion of either parietal lobe. Clinical investigati on of 13 patients demonstrated that the impairments affected both sides of the body. In mirror agnosia, the patients always reached toward the virtual object in the mirror and they were not capable of changing their behavior even after presentation of the position of the object in real visual space. In mirror ataxia (resembling optic ataxia) although some patients initiall y tended to reach for the virtual object in the mirror, they soon learned t o guide their arms toward the real object, all of them producing many direc tional errors. Both patient groups performed poorly on mental rotation, but only the patients with mirror agnosia were impaired in line orientation. O nly 1 of the patients suffered from neglect and 3 from apraxia Magnetic res onance imaging showed that in mirror agnosia the common zone of lesion over lap was scattered around the posterior angular gyrus/superior temporal gyru s and in mirror ataxia around the postcentral sulcus. We propose that both these clinical syndromes may represent different types of dissociation of r etinotopic space and body scheme, or likewise, of allocentric and egocentri c space normally adjusted in the parietal lobe.