Re: Crossed nonaphasia in a dextral with left hemispheric lesions: A functional magnetic resonance imaging study of mirrored brain organization - Response

To the Editor: We read with great interest the article by Hund-Georgiadis et al,1 in which they presented a case report of a patient with crossed nonaphasia after left-hemispheric stroke. Functional MRI revealed “mirrored” brain organization not only for language but also for divided/selective attention, as assessed by the Stroop task. Both functions were lateralized to the right hemisphere. The authors did not assess traditional right-hemispheric cognitive functions by means of functional MRI, such as visuospatial attention.2 They mention in their case description, however, that “the patient complained of problems in the visuospatial domain.” Neuropsychological testing revealed impaired processing of nonverbal material, whereas processing of verbal material was normal. Therefore, we suspect that visuospatial attention, which normally lateralizes to the right side of the brain, was lateralized to the left hemisphere in this case, providing further support for the authors’ claim that their patient showed “completely reversed,” ie, “mirrored,” cognitive functions. The case by Hund-Georgiadis et al agrees with our findings from a cohort of healthy subjects who were assessed for hemispheric dominance of language and visuospatial attention by means of functional transcranial Doppler ultrasonography and functional magnetic resonance tomography.3 We found that most subjects with atypical language lateralization indeed presented with a completely reversed brain organization, ie, visuospatial attention and language being lateralized into opposite hemispheres. Additionally, our study demonstrated that not only can completely reversed functional anatomy exist without obvious penalty to brain functions, but partially reversed functional anatomy can as well. Four of our 10 healthy subjects with right-hemispheric language dominance did not present with a “mirrored” brain organization. Rather, both language and visuospatial attention were lateralized to the same hemisphere. Furthermore, cognitive functions can vary significantly in the extent to which they lateralize. Clinicians need to be aware of the possibility of combined linguistic and visuospatial impairments of variable degrees after left- or right-hemispheric damage